Energy Forms, Transfer, and Conservation

Defining Energy and Work

Have you ever kicked a ball, pushed a toy car, or turned on a flashlight? All of these things use energy.

Energy is what helps things move, change, or do jobs. If something is moving, warming up, lighting up, or making sound, energy is involved.

We can think of energy as the ability to make something happen. Energy helps people, animals, machines, and even nature do work.

Work happens when a push or pull makes something move. If you push a box and it slides across the floor, you are doing work on the box.

If you push on a wall and it does not move, that is not work in science. A push or pull must make something move for work to happen.

So, a simple way to remember this is:

Energy helps do work, and work happens when a push or pull makes something move.

Scientists sometimes write work like this:

$$\text{work} = \text{force} \times \text{distance}$$

For 3rd grade, you do not need to solve hard math with this rule. It just helps us remember that work needs a push or pull and movement.

Main Ideas About Energy

• Energy can make things move.
• Energy can cause change.
• Energy can be transferred from one thing to another.
• Energy is needed to do work.

When you eat food, your body gets energy. That energy helps you run, jump, write, and play.

When you plug in a lamp, electrical energy helps the lamp shine. The energy causes a change: the bulb lights up.

When wind pushes a kite, the kite moves. The wind transfers energy to the kite.

Main Ideas About Work

• Work needs a push or pull.
• Work happens when that push or pull makes something move.
• If nothing moves, no work is done in science.

Let us look at some simple examples.

Example 1: Pushing a Toy Car

You push a toy car across the floor. Your hand gives the car a push. The car moves.

What is happening?

• Your body uses energy.
• Your hand pushes the car.
• The car moves.
• That means work is being done.

This is a clear example of energy helping you do work.

Example 2: Holding a Backpack

You pick up a backpack and hold it still. Your arms may feel tired, and your body is using energy.

But if the backpack is not moving, then in science we say work is not being done on the backpack at that moment.

What is happening?

• Your body uses energy to hold the backpack.
• The backpack does not move.
• So this is not work in the science meaning.

This can feel tricky, but remember: work needs movement.

Example 3: Lifting a Book

You lift a book from the floor to the table.

Step by step:

1. Your muscles use energy.
2. Your hand pulls the book upward.
3. The book moves upward.
4. You do work on the book.

This example shows that work can happen with a push or with a pull, as long as the object moves.

Example 4: Kicking a Soccer Ball

You kick a soccer ball, and it rolls across the grass.

What happened?

• Your body had energy from food.
• Your foot pushed the ball.
• The ball moved.
• You did work on the ball.

The ball now has energy for motion because of your kick.

How Energy and Work Fit Together

Energy and work are connected. Energy is the ability to make things happen. Work is one of the things energy helps us do.

If a person, animal, wind, water, or machine makes something move, energy is being used to do work.

Here are some everyday examples:

• A hammer hits a nail and moves it into wood.
• A student pulls open a door.
• A dog pushes a ball with its nose.
• A strong wind moves tree branches.

In each case, a push or pull causes movement, so work is done.

When Is It Not Work?

Sometimes energy is being used, but work is not happening in the science meaning.

• Pushing on a wall that stays still
• Holding a heavy bag without moving it
• Sitting still and thinking

These can take effort, but if an object does not move, it is not work in this lesson.

Energy Can Cause Change

Energy does not only help things move. It can also cause other changes.

• A toaster uses energy to heat bread.
• A lamp uses energy to make light.
• A speaker uses energy to make sound.

So energy can create motion, heat, light, and sound. In this lesson, we are focusing on how energy helps do work by causing movement.

Quick Check: Work or Not Work?

1. You push a swing, and it starts moving. Work
2. You lean on a fence, and it does not move. Not work
3. You pull a wagon, and it rolls forward. Work
4. You hold a book in the air without moving it. Not work

Easy Way to Remember

• Energy = the ability to make things happen
• Work = a push or pull that makes something move

Ask yourself two questions:

1. Was there a push or pull?
2. Did the object move?

If the answer to both is yes, then work happened.

Summary

Energy is the ability to do work, cause motion, or create change. Work happens when a push or pull makes an object move. If there is no movement, then no work is done in science. We see energy and work all around us when we push, pull, lift, kick, and move things.

Potential vs. Kinetic Energy

Energy is what helps things happen. Energy can make things move, change, or work.

In this lesson, you will learn about two important kinds of energy: potential energy and kinetic energy.

Potential energy is stored energy. It is energy that is waiting to be used.

Kinetic energy is energy of motion. If something is moving, it has kinetic energy.

Let’s think about a ball.

• A ball sitting still at the top of a hill has potential energy.
• When the ball rolls down the hill, it has kinetic energy.

This means energy can change from one form to another.

Main Idea: Stored energy can turn into moving energy.

1. What Is Potential Energy?

Potential energy is energy that is saved up. It is ready to be released later.

Something can have potential energy because of where it is or how it is being held.

Here are some examples of potential energy:

• A book resting on a high shelf
• A swing pulled back and held still
• A ball held up in your hand
• A stretched rubber band before it is let go

These things are not moving, but they have energy stored in them.

2. What Is Kinetic Energy?

Kinetic energy is the energy an object has when it is moving.

If something rolls, runs, falls, flies, or swings, it has kinetic energy.

Here are some examples of kinetic energy:

• A bike riding down the street
• A ball bouncing
• A child running on the playground
• A leaf blowing in the wind

When you see motion, you are seeing kinetic energy.

3. How Are They Different?

• Potential energy = stored energy
• Kinetic energy = moving energy

A good question to ask is: Is it moving?

• If no, it may have potential energy.
• If yes, it has kinetic energy.

4. Energy Can Change Forms

Energy does not just disappear. It can change from one kind to another.

For example, think about a roller coaster at the top of a hill. At the top, it has lots of potential energy because it is high up and waiting to move.

As the roller coaster goes down, its potential energy changes into kinetic energy. Now it is moving fast.

The same thing happens with many everyday objects.

• A dropped apple changes from potential energy to kinetic energy.
• A swing at the top has more potential energy.
• A swing moving through the air has kinetic energy.

5. Clues to Help You Decide

Use these clues to tell the difference:

1. Look for motion.
2. If the object is still, think about whether energy is being stored.
3. If the object is moving, it has kinetic energy.
4. If the object is high up, pulled back, or stretched, it may have potential energy.

Worked Example 1: Ball on a Table

A ball is sitting still on a table. Is it potential or kinetic energy?

Step 1: Is the ball moving? No.

Step 2: If it is not moving, the energy is stored.

Answer: The ball has potential energy.

Worked Example 2: Ball Falling

The same ball rolls off the table and falls down. Is it potential or kinetic energy?

Step 1: Is the ball moving? Yes.

Step 2: Moving objects have kinetic energy.

Answer: The falling ball has kinetic energy.

Worked Example 3: Swing on the Playground

A swing is pulled back and held still. Then it is let go and moves forward.

Part A: When the swing is pulled back and not moving, what kind of energy does it have?

It is being held still, so its energy is stored.

Answer: It has potential energy.

Part B: When the swing moves forward, what kind of energy does it have?

Now it is moving.

Answer: It has kinetic energy.

Worked Example 4: Rubber Band

You stretch a rubber band and hold it. Then you let it snap away.

Part A: While it is stretched and held still, the energy is stored.

Answer: That is potential energy.

Part B: When the rubber band flies through the air, it is moving.

Answer: That is kinetic energy.

Let’s Compare

Important Idea

Potential energy and kinetic energy are connected. Many times, stored energy changes into moving energy.

For example:

• held ball r dropped ball
• pulled-back swing r moving swing
• stretched rubber band r flying rubber band

Quick Check

• A child standing still at the top of a slide: potential energy
• A child sliding down the slide: kinetic energy
• A toy on a shelf: potential energy
• A toy car zooming across the floor: kinetic energy

Summary

Potential energy is stored energy. It is energy waiting to be used.

Kinetic energy is energy of motion. If something is moving, it has kinetic energy.

You can tell the difference by asking, “Is it moving?” If it is still, it may have potential energy. If it is moving, it has kinetic energy.

Energy can change forms. Stored energy can turn into moving energy in many everyday situations.

Forms of Energy

Everything we do uses energy. Energy is what makes things happen. It can make things move, light up, make sounds, or feel warm.

We cannot always see energy, but we can see what it does. A lamp shines because of energy. A drum makes sound because of energy. A rolling ball moves because of energy.

There are different forms of energy. In this lesson, we will learn about five important kinds:

• Thermal energy — heat
• Radiant energy — light
• Acoustic energy — sound
• Mechanical energy — motion and movement
• Electrical energy — energy from electricity

Let’s look at each form of energy one at a time.

1. Thermal Energy

Thermal energy is heat energy. It is the energy that makes things warmer.

You can feel thermal energy from the Sun on your skin. You can also feel it from a heater, a campfire, or a warm cup of soup.

Things with more heat have more thermal energy. Things that feel cold have less thermal energy.

• A stove warming a pan
• The Sun heating the sand
• Hot chocolate in a mug

2. Radiant Energy

Radiant energy is light energy. It travels as light that we can often see.

The Sun is a big source of radiant energy. Light bulbs, flashlights, and candles also give off radiant energy.

• Sunlight shining through a window
• A flashlight in a dark room
• A lamp lighting a book so you can read

3. Acoustic Energy

Acoustic energy is sound energy. It is made when something vibrates, or shakes back and forth very fast.

When you clap your hands, ring a bell, or play music, you are making acoustic energy.

• A dog barking
• A drum being hit
• A person talking

4. Mechanical Energy

Mechanical energy is the energy of movement. When something moves, it has mechanical energy.

A bike rolling down the street, a child swinging, and a bouncing ball all show mechanical energy.

• A soccer ball being kicked
• A car driving
• A fan spinning

5. Electrical Energy

Electrical energy is energy carried by electricity. It powers many things we use every day.

Televisions, computers, lamps, and refrigerators can use electrical energy. Batteries can also provide electrical energy.

• A lamp plugged into a wall
• A toy using batteries
• A phone charging

Energy Can Change Forms

Energy can change from one form to another. This happens all the time.

For example, in a flashlight, electrical energy changes into radiant energy and a little thermal energy. The flashlight shines light and may feel a little warm.

In a drum, mechanical energy from hitting the drum changes into acoustic energy. That is why we hear a sound.

In a toaster, electrical energy changes into thermal energy. The toaster gets hot and warms the bread.

How to Tell the Forms of Energy Apart

• If something feels warm or hot, it shows thermal energy.
• If something gives off light, it shows radiant energy.
• If something makes a sound, it shows acoustic energy.
• If something is moving, it shows mechanical energy.
• If something is powered by electricity, it uses electrical energy.

Worked Example 1

Question: A lamp is turned on. What form of energy do you notice?

Step 1: Ask, “What does the lamp do?” It lights up.

Step 2: Light is radiant energy.

Answer: The lamp shows radiant energy. If it is plugged in, it also uses electrical energy.

Worked Example 2

Question: You hit a drum with your hand. What forms of energy are involved?

Step 1: Your hand moves. Movement is mechanical energy.

Step 2: The drum makes sound. Sound is acoustic energy.

Answer: The energy changes from mechanical energy to acoustic energy.

Worked Example 3

Question: A toaster warms bread. What form of energy does it make?

Step 1: The toaster uses electricity, so it starts with electrical energy.

Step 2: The bread gets warm. Heat is thermal energy.

Answer: The toaster changes electrical energy into thermal energy.

Worked Example 4

Question: A child kicks a soccer ball across the grass. What form of energy is easiest to see?

Step 1: Look for what is happening. The ball is moving.

Step 2: Movement is mechanical energy.

Answer: The easiest form of energy to see is mechanical energy.

Quick Practice

1. A flashlight shines in the dark. Which form of energy do you see?
2. A bell rings. Which form of energy do you hear?
3. The Sun warms your face. Which form of energy do you feel?
4. A battery powers a toy car. Which form of energy comes from the battery?
5. A skateboard rolls down a hill. Which form of energy does the moving skateboard show?

Quick Practice Answers

1. Radiant energy
2. Acoustic energy
3. Thermal energy
4. Electrical energy
5. Mechanical energy

Remember

Sometimes one object shows more than one form of energy at the same time. A lamp can use electrical energy, give off radiant energy, and also make a little thermal energy.

When you answer questions about forms of energy, look for clues:

• Hot = thermal
• Light = radiant
• Sound = acoustic
• Movement = mechanical
• Electricity = electrical

Summary

Energy makes things happen. The five forms of energy in this lesson are thermal, radiant, acoustic, mechanical, and electrical.

We can identify forms of energy by what they do. Heat is thermal, light is radiant, sound is acoustic, movement is mechanical, and electricity is electrical. Energy can also change from one form into another.

Energy Transformation and Conversion

Energy is what helps things move, change, grow, and work. We use energy every day when we turn on lights, ride in a car, or toast bread.

Sometimes energy stays in the same form, but very often it changes from one form to another. When energy changes form, we call it an energy transformation or energy conversion.

For example, a lamp uses electrical energy. When the lamp is on, that electrical energy changes into light energy and a little thermal energy, which is heat.

Big idea: Energy can change forms, but it does not disappear. It moves or changes into another kind of energy.

Some common forms of energy

• Electrical energy — energy that powers things like TVs, lamps, and toasters
• Thermal energy — heat energy
• Light energy — energy we can see
• Sound energy — energy we hear
• Motion energy — energy of moving things
• Chemical energy — energy stored in food, batteries, and fuel

Why do energy changes happen?

Machines and objects need energy to do a job. Many devices take in one form of energy and change it into another form that is useful.

A toaster is a great example. It takes in electrical energy. Then it changes that energy into thermal energy to heat the bread. It also gives off a little light energy from the glowing heating wires.

So we can describe the toaster like this:

electrical energy → thermal energy + light energy

Energy can change in many directions

Energy does not always change in the same way. Different objects transform energy in different patterns.

• A flashlight changes chemical energy in its batteries into electrical energy, and then into light energy and a little thermal energy.
• A fan changes electrical energy into motion energy when the blades spin. It also makes a little sound energy.
• A car changes chemical energy in fuel into motion energy, sound energy, and thermal energy.
• Your body changes chemical energy from food into motion energy and thermal energy.

Energy can transfer too

Energy can also move from one object to another. This is called energy transfer.

For example, when a toaster heats bread, thermal energy transfers from the hot toaster wires to the bread. The bread gets warmer because energy moved to it.

Another example is the Sun. The Sun gives off light and thermal energy. That energy travels to Earth and warms the ground, water, plants, and people.

Energy is conserved

A very important science idea is that energy is conserved. That means energy is not made from nothing, and it does not vanish. It changes form or moves from place to place.

When a bulb shines, the electrical energy did not disappear. It changed mostly into light energy and some thermal energy.

We can think of it like this:

Energy in = Energy out

Sometimes the energy out is in more than one form. A device may give off light, sound, heat, or motion all at the same time.

Worked Example 1: Lamp

Question: What energy transformation happens in a lamp?

Step 1: Think about what goes into the lamp. A lamp plugs into an outlet, so it uses electrical energy.

Step 2: Think about what comes out. A lamp gives off light energy. It also gets warm, so it gives off some thermal energy.

Answer: A lamp changes electrical energy into light energy and thermal energy.

Worked Example 2: Toaster

Question: A toaster browns bread. What energy transformation happens?

Step 1: The toaster uses electrical energy from the wall.

Step 2: The toaster becomes hot, so it makes thermal energy.

Step 3: The wires may glow, so it also makes a little light energy.

Answer: A toaster changes electrical energy into thermal energy and light energy.

Worked Example 3: Flashlight

Question: How does energy change in a flashlight?

Step 1: The batteries store chemical energy.

Step 2: When the flashlight is turned on, that chemical energy becomes electrical energy.

Step 3: The electrical energy becomes mostly light energy and a little thermal energy.

Answer: A flashlight changes chemical energy → electrical energy → light energy + thermal energy.

Worked Example 4: Riding a Bike

Question: What energy transformation happens when you ride a bike?

Step 1: Your body gets energy from food. Food stores chemical energy.

Step 2: Your legs push the pedals, so the bike moves. That is motion energy.

Step 3: Your body also gives off heat, so some energy becomes thermal energy.

Answer: Riding a bike changes chemical energy from food into motion energy and thermal energy.

How to figure out an energy transformation

1. Ask: What energy goes in?
2. Ask: What does the object do?
3. Ask: What energy comes out?
4. Remember that more than one kind of energy can come out.

Here are some quick examples:

• Speaker: electrical energy → sound energy
• Blender: electrical energy → motion energy + sound energy
• Television: electrical energy → light energy + sound energy + thermal energy
• Campfire: chemical energy in wood → thermal energy + light energy

Important things to remember

• Energy helps things work and change.
• Energy can change from one form to another.
• This change is called an energy transformation or conversion.
• Energy can also move from one object to another.
• Energy is conserved, which means it does not disappear.

Brief Summary

Devices and living things use energy in many ways. A toaster, lamp, flashlight, fan, and even your body all change energy from one form into another form.

When you study energy transformation, always look for the energy going in and the energy coming out. Remember: energy can change form and transfer, but it is not lost.

Reflection and Scattering of Light

Light is a kind of energy that helps us see. It travels from a light source, like the Sun, a lamp, or a flashlight. When light hits an object, different things can happen.

Sometimes light bounces back. This is called reflection. Sometimes light is sent in many directions. This is called scattering.

Learning about reflection and scattering helps us understand why mirrors work, why we can see many objects around us, and why some things look shiny while others do not.

What Is Reflection?

Reflection happens when light hits a surface and bounces off it. A very smooth surface reflects light in a neat, predictable way.

When a surface is smooth, the light rays stay organized after they bounce. That is why smooth surfaces, like mirrors, can make clear images.

• Mirror
• Calm water
• Shiny metal spoon

These surfaces are smooth, so light bounces off them in a more regular way.

What Is Scattering?

Scattering happens when light hits a rough surface and bounces in many directions. The light does not stay neat and organized.

Because the light spreads out, rough surfaces usually do not make clear images. But scattering is still very helpful. It lets us see objects from many directions.

• Paper
• Sidewalk
• Wall
• Tree bark

These surfaces are rougher, so they scatter light.

Smooth Surfaces and Rough Surfaces

A smooth surface has very tiny bumps or almost no bumps. Light bounces off it in a regular way.

A rough surface has many tiny bumps. Even if it feels smooth to your hand, it can still be rough to light. Those tiny bumps make the light bounce in different directions.

We can think about it like this:

• Smooth surface = light bounces back in a more predictable way
• Rough surface = light scatters in many directions

Why Mirrors Make Clear Images

A mirror is very smooth. Light from your face hits the mirror and reflects in an organized way. That reflected light travels to your eyes, and you see your image.

If the surface were rough, the light from your face would scatter. Then your eyes would not get a clear picture.

Why We Can See Most Objects

Most objects around us are not mirrors. A book, a desk, a shoe, and a wall all scatter light. Light from the Sun or a lamp hits them, then scatters in many directions.

Some of that scattered light enters your eyes. That is how you can see the objects.

So, scattering is very important in everyday life. Without it, many things would be much harder to see.

Light and Direction

Light travels in straight paths. When it hits a smooth surface, it bounces off in a more regular path. When it hits a rough surface, the tiny bumps send the light in many paths.

You do not need to memorize hard rules. Just remember:

• Smooth surface: light bounces back neatly
• Rough surface: light spreads out

Examples in Daily Life

• You look in a mirror and see your face because of reflection.
• You can see a classroom wall from many seats because the wall scatters light.
• A calm pond may reflect trees and clouds because the water is smooth.
• A crumpled piece of paper scatters light, so it does not show a clear image.

Worked Example 1

Question: Mia shines a flashlight at a mirror. Will the light reflect or scatter?

Step 1: Think about the surface. A mirror is very smooth.

Step 2: Smooth surfaces reflect light in a predictable way.

Answer: The light will reflect.

Worked Example 2

Question: Ben shines a flashlight at a brick wall. Will the light reflect neatly or scatter?

Step 1: Think about the surface. A brick wall is rough.

Step 2: Rough surfaces scatter light in many directions.

Answer: The light will scatter.

Worked Example 3

Question: Ava can see her face in a still pond, but not in choppy water. Why?

Step 1: Still water is smoother than choppy water.

Step 2: Smooth water reflects light more regularly, so it can make an image.

Step 3: Choppy water has many moving bumps, so the light scatters more.

Answer: Ava sees her face in still water because the smooth surface reflects light. She cannot see a clear image in choppy water because the light scatters.

Worked Example 4

Question: Why can students around a classroom all see the same poster on the wall?

Step 1: The poster is not a mirror, so it does not reflect light in just one neat direction.

Step 2: The poster's surface scatters light in many directions.

Step 3: Light from the poster can reach many students' eyes.

Answer: Many students can see the poster because it scatters light in many directions.

How Reflection and Scattering Are Alike and Different

Both reflection and scattering happen when light hits a surface and bounces off.

The difference is how the light bounces:

• Reflection: light bounces off a smooth surface in a regular way
• Scattering: light bounces off a rough surface in many directions

Quick Check

1. What kind of surface makes a clear image?
2. Does a rough surface reflect neatly or scatter?
3. Why can you see a book even though it is not shiny?
4. Which is more likely to show your face clearly: a mirror or a sidewalk?

Answers to the Quick Check

1. A smooth surface, like a mirror, makes a clear image.
2. A rough surface scatters light.
3. You can see a book because it scatters light into your eyes.
4. A mirror is more likely to show your face clearly.

Summary

Light is energy that helps us see. When light hits an object, it can bounce off.

If the surface is smooth, the light reflects in a regular, predictable way. This can make a clear image, like in a mirror.

If the surface is rough, the light scatters in many directions. Scattering helps us see many everyday objects, even when they are not shiny.

Shadow Formation and Dynamics

Have you ever seen your shadow on the ground on a sunny day? A shadow appears when light is blocked. Shadows are all around us. We can see them outside in the Sun, inside with a lamp, and even when we hold an object in front of a flashlight.

In this lesson, you will learn how shadows form, why they change size, and why some shadows look dark and sharp while others look lighter or blurrier.

1. What is a shadow?

A shadow is a dark shape made when an object blocks light. Light travels from a source, like the Sun, a lamp, or a flashlight. If something gets in the way, the light cannot pass through that object, so a shadow forms behind it.

Think of light like many straight paths moving forward. When an object blocks those paths, the area behind the object gets less light. That darker area is the shadow.

2. What kinds of objects make shadows?

Objects that are opaque make strong shadows. Opaque means light cannot pass through them. A book, a wall, a toy block, and your body are opaque.

Some objects let a little light through. These objects may make faint shadows. But the clearest shadows happen when opaque objects block the light.

• Opaque object: blocks light and makes a clear shadow
• Light source: where the light comes from, such as the Sun or a flashlight
• Shadow: the dark area where light is blocked

3. Shadows need three things

To make a shadow, you need:

1. a light source
2. an opaque object
3. a surface for the shadow to appear on, like the ground, a wall, or paper

If one of these is missing, you may not see a shadow clearly.

4. Why do shadows change?

Shadows do not always stay the same. They can change in size, shape, and sharpness. This happens because the light source and the object can move.

The two big things that change a shadow are:

• the angle of the light
• the distance between the light source and the object

5. How the angle of light changes a shadow

Angle means the direction the light is shining from. When light shines from high above, the shadow is usually shorter. When light shines from the side, the shadow is usually longer.

This is why your shadow changes during the day. When the Sun is high in the sky around the middle of the day, your shadow is shorter. In the morning or late afternoon, when the Sun is lower in the sky, your shadow is longer.

Here is the idea:

• Light high above → shorter shadow
• Light lower in the sky → longer shadow

6. How distance changes a shadow

The shadow also changes when the light source moves closer to or farther from the object.

If a flashlight is moved closer to an object, the shadow often looks bigger. If the flashlight is moved farther away, the shadow often looks smaller.

You can test this with your hand and a flashlight. Shine the flashlight on your hand near a wall. Move the flashlight closer to your hand and watch the shadow grow. Move it away and watch the shadow shrink.

7. Why some shadows are sharp and some are blurry

Some shadows have edges that look sharp, which means clear and easy to see. Other shadows have edges that look blurry, which means not as clear.

A shadow is often sharper when the light is steady and the object is in a good position to block it clearly. A shadow can look blurrier when the light spreads out more or when the object is placed differently.

For example, a flashlight very close to an object can make a larger shadow that may also look less sharp. A flashlight farther away may make a smaller, clearer shadow.

8. Shape of the shadow

The shape of a shadow depends on the shape of the object and the direction of the light. A round ball may make a round shadow from one direction, but from another direction the shadow may look different.

If you turn an object, its shadow can change shape too. That is because different parts of the object block the light in different ways.

Worked Example 1: Making a basic shadow

Question: A student shines a flashlight at a toy block and holds a piece of paper behind it. Will a shadow form?

Step 1: Is there a light source? Yes, the flashlight.

Step 2: Is there an opaque object? Yes, the toy block.

Step 3: Is there a surface for the shadow? Yes, the paper.

Answer: Yes. The toy block blocks the light, so a shadow forms on the paper.

Worked Example 2: Changing the light angle

Question: Mia stands outside in the morning and sees a long shadow. Later, at noon, her shadow looks shorter. Why?

Step 1: In the morning, the Sun is lower in the sky.

Step 2: Lower-angle light makes longer shadows.

Step 3: At noon, the Sun is higher in the sky.

Step 4: Higher-angle light makes shorter shadows.

Answer: Mia's shadow changes because the angle of the Sun's light changes during the day.

Worked Example 3: Moving the flashlight

Question: Ben shines a flashlight at his hand to make a shadow on the wall. Then he moves the flashlight closer to his hand. What will most likely happen to the shadow?

Step 1: The light source moves closer to the object.

Step 2: When the light gets closer, the shadow often gets bigger.

Answer: The shadow will most likely become bigger.

Worked Example 4: Sharp or blurry?

Question: A student notices that one shadow has very clear edges, and another shadow has edges that are fuzzy. What is the difference?

Step 1: A clear-edged shadow is called sharp.

Step 2: A fuzzy-edged shadow is called blurry.

Step 3: The light's position and distance can change how sharp the shadow looks.

Answer: One shadow is sharp and the other is blurry because the light and object are arranged differently.

9. Try it yourself

You can explore shadows with simple materials:

• a flashlight
• a small opaque object, like a block or spoon
• a wall or sheet of paper

Try these steps:

1. Shine the flashlight at the object.
2. Look at the shadow on the wall or paper.
3. Move the flashlight closer. What happens to the shadow size?
4. Move the flashlight farther away. What changes?
5. Move the flashlight higher or lower. Does the shadow get longer or shorter?
6. Turn the object. Does the shadow shape change?

This is a great way to see that shadows are not fixed. They change when the light or object changes.

10. Important ideas to remember

• Shadows form when light is blocked.
• Opaque objects make the clearest shadows.
• A shadow needs a light source, an object, and a surface.
• The angle of the light can make a shadow longer or shorter.
• The distance from the light to the object can make a shadow bigger or smaller.
• Shadows can look sharp or blurry.

Brief Summary

A shadow is made when an opaque object blocks light. Shadows can change depending on where the light is and how far it is from the object. When the light angle changes, the shadow can become longer or shorter. When the light moves closer or farther away, the shadow can become bigger or smaller. By watching shadows, we can learn how light travels and how objects block it.

Acoustic energy is the energy of sound. We hear sound when something vibrates.

A vibration is a quick back-and-forth motion. When an object shakes or moves back and forth, it can make sound.

Think about a drum. When you hit the drum, the drum skin vibrates. Those vibrations move through the air and travel to your ears. Then you hear the sound.

Sound is a kind of mechanical energy. That means sound needs matter to travel through, like air, water, or solids. Sound cannot travel where there is no matter.

Sound travels in waves. A sound wave is the way the vibration moves from one place to another.

For sound, the waves push matter forward and backward. These are called longitudinal waves. You do not need to remember that big word perfectly. Just remember this: sound waves move by pushing and squeezing matter.

Imagine people standing in a line with a slinky. If one person pushes the slinky forward and pulls it back, the squeeze moves down the slinky. Sound waves move in a similar way through air.

In air, sound waves make tiny pushes called compressions, where air is squeezed together. Then they make spaces where air spreads back out. This squeezing and spreading keeps moving outward.

Even though the sound wave travels, the air does not travel all the way from the drum to your ear. The air particles only move a little bit back and forth. The energy moves through the air.

Main Ideas

1. Sound starts with vibration.

• A guitar string vibrates when you pluck it.
• A bell vibrates when you ring it.
• Your vocal cords vibrate when you talk or sing.
• A speaker vibrates to make music.

If nothing vibrates, no sound is made.

2. Sound needs a material to travel through.

• Sound can travel through air.
• Sound can travel through water.
• Sound can travel through solids, like wood or metal.

That is why you can hear someone knock on a door from the other side. The sound moves through the solid door and the air too.

3. Sound moves as waves.

Sound spreads outward from where it starts. If you clap your hands, the sound moves away from your hands in all directions.

The wave carries energy from the source, or starting place, to other places.

4. Sound can be loud or soft.

A stronger vibration makes a louder sound. A weaker vibration makes a softer sound.

• Hitting a drum hard makes a loud sound.
• Tapping it gently makes a soft sound.

5. Sound can be high or low.

Some sounds are high, like a bird chirping. Some sounds are low, like a big drum.

Fast vibrations usually make higher sounds. Slow vibrations usually make lower sounds.

6. Sound energy can transfer from one thing to another.

When you speak, your vocal cords vibrate. That vibration transfers energy to the air. The air transfers the energy to your friend’s ear. Then your friend hears your voice.

This is an example of energy transfer.

Everyday Examples of Sound Energy

• Clapping hands: Your hands hit together and make the air vibrate.
• School bell: The bell vibrates and sends sound waves through the air.
• Talking: Your throat vibrates and makes sounds.
• Thunder: The air vibrates from lightning’s energy, making a loud sound.
• Knocking on a table: The table and air both help carry the sound.

Worked Examples

Example 1: Why does a drum make sound?

Question: A student hits a drum. How does the sound happen?

Step 1: The student hits the drum skin.

Step 2: The drum skin vibrates.

Step 3: The vibrations push the air.

Step 4: The sound wave travels through the air to your ears.

Answer: The drum makes sound because its drum skin vibrates and sends sound waves through the air.

Example 2: Loud or soft?

Question: Two students tap the same bell. One taps gently. One taps hard. Which sound is louder, and why?

Step 1: A gentle tap makes a small vibration.

Step 2: A hard tap makes a stronger vibration.

Step 3: Stronger vibrations make louder sounds.

Answer: The hard tap is louder because it makes stronger vibrations.

Example 3: Can sound travel through a desk?

Question: A child taps one end of a desk, and another child puts an ear on the other end. Can the second child hear it?

Step 1: Tapping makes the desk vibrate.

Step 2: Sound can travel through solids.

Step 3: The vibration moves through the desk to the other child.

Answer: Yes. Sound can travel through the solid desk.

Example 4: What is the source of the sound?

Question: A student hears a guitar. What is vibrating to make the sound?

Step 1: Look for the part that moves back and forth.

Step 2: On a guitar, the strings vibrate when plucked.

Step 3: Those vibrations move through the air as sound waves.

Answer: The guitar strings are vibrating, and that makes the sound.

Things to Remember

• Sound is energy.
• Sound begins with vibration.
• Sound travels in waves.
• Sound needs matter like air, water, or solids to travel.
• Stronger vibrations make louder sounds.
• Faster vibrations often make higher sounds.

Quick Check

1. What must happen for sound to start?
2. Does sound travel in waves or does it stay still?
3. Can sound travel through water?
4. Which is louder: a strong vibration or a weak vibration?
5. What vibrates when you speak?

Answers:

1. Something must vibrate.
2. Sound travels in waves.
3. Yes, sound can travel through water.
4. A strong vibration is louder.
5. Your vocal cords vibrate when you speak.

Brief Summary

Sound is a form of energy called acoustic energy. It starts when something vibrates. The vibration moves through matter like air, water, or solids as sound waves. These waves carry energy to our ears so we can hear. Strong vibrations make louder sounds, and faster vibrations usually make higher sounds.

Sound Propagation Through Media means learning how sound travels from one place to another.

When you hear a drum, a bell, or a person talking, sound is moving to your ears. But sound cannot move by itself. Sound needs matter to travel through. Matter can be a solid, liquid, or gas. These are called media. The word medium means one kind of material sound can travel through.

For example, sound can travel through:

• Solids like wood, metal, or a wall
• Liquids like water
• Gases like the air around us

Most of the sounds we hear every day travel through air, which is a gas.

How does sound move?

Sound is made when something vibrates. Vibrate means to move back and forth very quickly.

When a guitar string is plucked, it vibrates. When a drum is hit, the drum skin vibrates. When you speak, parts of your throat vibrate.

These vibrations make the tiny pieces of matter nearby move. Then those tiny pieces bump into other tiny pieces. This keeps happening, and the sound moves along through the material until it reaches your ears.

You can think of it like a line of people gently tapping the next person in line. The movement passes along from one to the next.

Sound needs a medium

Sound cannot travel where there is no matter. If there is no air, no water, and no solid to move the vibrations along, sound cannot be heard.

So, sound needs a medium to travel through.

Sound can travel through different kinds of media

1. Through gases

   Sound travels through air all around us. When your teacher talks, the sound moves through the air to your ears.

2. Through liquids

   Sound can also travel through water. If two swimmers are under water, they may hear sounds in the water.

3. Through solids

   Sound travels very well through solids. If you put your ear gently against a table, you may hear a tap on the table from farther away.

Which medium lets sound travel fastest?

Sound travels at different speeds in different materials.

• Fastest in solids
• Slower in liquids
• Slowest in gases

This happens because the tiny pieces of matter are packed closer together in solids. That helps the vibrations pass along more quickly.

In liquids, the pieces are a little farther apart than in solids, so sound moves, but not as fast.

In gases like air, the pieces are spread out more, so sound moves the slowest there.

A simple way to remember this is:

solids → fastest, liquids → middle, gases → slowest

Everyday examples

• You hear a friend talking because sound travels through air.
• You may hear a train sooner by putting your ear near the track because sound travels well through the solid metal.
• Dolphins and whales use sound in water.
• If someone knocks on a door, the sound travels through the solid door and the air.

Worked Example 1

Question: A girl claps her hands. How does the sound get to her friend across the room?

Step 1: The clap makes vibrations.

Step 2: The vibrations move through the air.

Step 3: The sound reaches the friend’s ears.

Answer: The sound travels through the gas in the room, which is air.

Worked Example 2

Question: Ben taps one end of a wooden table. His sister puts her ear on the other end. Can she hear it?

Step 1: The tap makes the table vibrate.

Step 2: The sound travels through the solid wood.

Step 3: The vibration reaches her ear.

Answer: Yes. Sound can travel through a solid, like wood.

Worked Example 3

Question: Put these in order from fastest sound travel to slowest: air, water, metal.

Step 1: Metal is a solid.

Step 2: Water is a liquid.

Step 3: Air is a gas.

Step 4: Remember the rule: solids fastest, liquids next, gases slowest.

Answer: metal, water, air

Worked Example 4

Question: A student says, “Sound can travel without anything in the way.” Is that correct?

Step 1: Think about what sound needs.

Step 2: Sound needs a medium, like air, water, or a solid.

Answer: No, that is not correct. Sound needs matter to travel through.

Tips to help you remember

• Sound starts with vibrations.
• Sound needs matter to travel.
• Media are materials like solids, liquids, and gases.
• Sound travels fastest in solids.
• Sound travels through air, water, and solids.

Quick check

• Does sound need a medium? Yes.
• Can sound travel through air? Yes.
• Can sound travel through water? Yes.
• Can sound travel through solids? Yes.
• Where does sound travel fastest? In solids.

Summary

Sound is made by vibrations. Those vibrations move through matter.

Sound needs a medium to travel. A medium can be a solid, liquid, or gas.

Sound can travel through all three, but it moves fastest in solids, slower in liquids, and slowest in gases.

Frequency, Pitch, and Amplitude

Have you ever heard a tiny bird make a high sound and a big drum make a low sound? Sounds can be high, low, loud, or quiet. We can learn about these sounds by thinking about vibrations.

A vibration is a quick back-and-forth movement. Sound is made when something vibrates. A guitar string vibrates. A drumhead vibrates. Even your vocal cords vibrate when you speak or sing.

There are two big ideas to learn:

• Frequency helps tell us the pitch of a sound.
• Amplitude helps tell us the volume of a sound.

Let’s learn what each one means.

1. Frequency and Pitch

Frequency means how fast something vibrates. If it vibrates many times in a short time, it has a high frequency. If it vibrates fewer times in the same time, it has a low frequency.

Pitch is how high or low a sound seems to our ears.

• High frequency makes a high pitch.
• Low frequency makes a low pitch.

Think about a whistle and a tuba:

• A whistle usually makes a high-pitched sound, so it has fast vibrations.
• A tuba usually makes a low-pitched sound, so it has slower vibrations.

You can remember it like this: faster vibrations = higher sound.

2. Amplitude and Volume

Amplitude means how big the vibration is. A big vibration has more amplitude. A small vibration has less amplitude.

Volume is how loud or quiet a sound is.

• Big vibrations make a louder sound.
• Small vibrations make a quieter sound.

Think about hitting a drum:

• If you tap it gently, the drum vibrates a little. The sound is quiet.
• If you hit it harder, the drum vibrates more. The sound is loud.

You can remember it like this: bigger vibrations = louder sound.

3. Pitch and Volume Are Not the Same

Sometimes students mix up pitch and volume. They are different.

• Pitch tells if a sound is high or low.
• Volume tells if a sound is loud or quiet.

A sound can be:

• high and quiet, like a soft bird chirp
• high and loud, like a loud whistle
• low and quiet, like a soft drum beat
• low and loud, like a big drum played strongly

4. How Energy Is Part of Sound

Sound is a form of energy. When something vibrates, it sends sound energy through the air. That sound can travel to your ears.

When you make a vibration stronger, it often has more energy and makes a bigger vibration. Bigger vibrations have greater amplitude, so the sound is louder.

When something vibrates faster, the sound has a higher pitch.

5. Picture It in Your Mind

Imagine drawing two wavy lines.

For pitch:

• If the waves are packed close together, that shows faster vibrations and a higher pitch.
• If the waves are spread out more, that shows slower vibrations and a lower pitch.

For volume:

• If the waves are tall, that shows greater amplitude and a louder sound.
• If the waves are short, that shows smaller amplitude and a quieter sound.

You do not need to measure the waves with numbers to understand the idea. Just remember:

• close together = high pitch
• farther apart = low pitch
• tall waves = loud
• short waves = quiet

Worked Example 1: Bird and Drum

Question: A bird chirps with a high sound. A big drum makes a low boom. Which one has the higher frequency?

Think: Higher pitch means faster vibrations. Faster vibrations mean higher frequency.

Answer: The bird chirp has the higher frequency because it has the higher pitch.

Worked Example 2: Soft Tap and Hard Hit

Question: You tap a drum softly once, then hit it harder the next time. Which sound has greater amplitude?

Think: Greater amplitude means bigger vibrations. Bigger vibrations make louder sounds.

Answer: The harder hit has greater amplitude because it makes a louder sound.

Worked Example 3: Same Pitch, Different Volume

Question: Mia blows a whistle softly. Then she blows the same whistle again, but louder. Did the pitch change, the amplitude change, or both?

Think: It is the same whistle making the same kind of note, so the sound can stay high. But one sound is louder than the other.

Answer: The amplitude changed because the volume changed. The pitch can stay the same.

Worked Example 4: Two Guitar Strings

Question: One guitar string makes a high note. Another guitar string makes a low note. Which string is vibrating faster?

Think: High pitch means high frequency. High frequency means faster vibrations.

Answer: The string making the high note is vibrating faster.

6. Helpful Clues to Remember

• Frequency = how fast something vibrates
• Pitch = how high or low a sound is
• Amplitude = how big the vibration is
• Volume = how loud or quiet a sound is

And the two most important rules are:

• Fast vibrations → high pitch
• Big vibrations → loud volume

7. Try It in Real Life

You can notice these ideas around you every day:

• A small bell often has a high pitch.
• A large drum often has a low pitch.
• A gentle clap is quiet and has smaller amplitude.
• A strong clap is loud and has greater amplitude.

When you listen carefully, you can ask:

1. Is the sound high or low? That tells about pitch and frequency.
2. Is the sound loud or quiet? That tells about volume and amplitude.

Summary

Sound is made by vibrations. Frequency tells how fast something vibrates, and that affects pitch. Faster vibrations make a higher pitch, and slower vibrations make a lower pitch.

Amplitude tells how big the vibration is, and that affects volume. Bigger vibrations make louder sounds, and smaller vibrations make quieter sounds.

If you remember these two ideas, you will understand the lesson well:

• frequency → pitch
• amplitude → volume

Heat is energy that makes things warmer. Heat likes to move from something warmer to something cooler.

There are 3 main ways heat can move:

• Conduction — heat moves by touching
• Convection — heat moves in moving liquids or gases
• Radiation — heat moves by waves and does not need touching

Let’s learn each one step by step.

1. Conduction

Conduction happens when heat moves through things that are touching. If one object is warm and it touches a cooler object, heat moves from the warmer object to the cooler one.

You can think of conduction as heat being passed along by a handshake from one tiny part to the next.

Examples of conduction:

• A metal spoon in hot soup gets warm.
• Your hand feels warm when you hold a hot mug.
• An ice cube melts faster in your hand than on a table.

Some materials let heat move through them easily. Metal is very good at conduction. Other materials, like wood, plastic, and cloth, do not let heat move as easily.

That is why a metal pan gets hot on the stove, but the pan may have a plastic or wooden handle to help protect your hand.

2. Convection

Convection happens in liquids and gases. Heat moves because the liquid or gas itself moves around.

When part of a liquid or gas gets warm, it often rises. Cooler parts move down. This movement makes a circle of motion that carries heat from place to place.

Examples of convection:

• Water boiling in a pot
• Warm air rising from a heater
• Cool air moving in after warm air rises

Imagine soup heating on the stove. The soup at the bottom gets hot first. It rises up. Cooler soup moves down to take its place. Then that cooler soup gets heated too. This keeps happening, and the soup warms all around.

3. Radiation

Radiation is heat that travels by waves. Radiation does not need touching. It can move through the air and even through space.

The biggest example of radiation is the Sun. The Sun warms your face even though it is very far away. The heat travels from the Sun to Earth by radiation.

Examples of radiation:

• Feeling the Sun warm your skin
• Feeling heat from a campfire without touching it
• Feeling warmth from a toaster

With radiation, you do not have to touch the warm thing. You can feel the heat from a short distance away.

How are they different?

• Conduction: heat moves by direct touch
• Convection: heat moves by moving liquid or gas
• Radiation: heat moves by waves, without touching

A good way to remember them is:

• Conduction = contact
• Convection = circle-moving liquid or gas
• Radiation = rays

Heat always moves from warmer to cooler.

If a hot cocoa mug warms your hands, the heat is moving from the hot mug to your cooler hands. If the Sun warms the sidewalk, the heat is moving from the warmer sunlight to the cooler sidewalk.

Worked Example 1: Spoon in Hot Soup

A metal spoon sits in a bowl of hot soup. After a little while, the handle of the spoon feels warm. What kind of heat transfer is this?

Step 1: Is something touching? Yes. The hot soup touches the spoon.

Step 2: Does heat move through the spoon by contact? Yes.

Answer: This is conduction.

Worked Example 2: Boiling Water

A pot of water is heating on the stove. The water at the bottom gets hot first, rises, and cooler water sinks. What kind of heat transfer is this?

Step 1: Is a liquid moving? Yes. Water is moving up and down.

Step 2: Is the moving water carrying heat? Yes.

Answer: This is convection.

Worked Example 3: Warm Sunlight

You stand outside and feel the Sun warming your face. You are not touching the Sun. What kind of heat transfer is this?

Step 1: Are you touching the warm source? No.

Step 2: Is heat traveling from far away? Yes.

Answer: This is radiation.

Worked Example 4: Which One Is It?

Look at each situation and choose the kind of heat transfer.

1. A child holds an ice cube, and it melts quickly.
   Answer: Conduction, because the hand touches the ice cube.
2. Warm air rises from a floor heater and moves around the room.
   Answer: Convection, because moving air carries the heat.
3. You feel heat from a campfire while sitting nearby.
   Answer: Radiation, because you feel heat without touching the fire.

Helpful Clues

• If things are touching, think conduction.
• If a liquid or gas is moving, think convection.
• If heat comes from a distance by waves, think radiation.

Why this matters

We use heat transfer every day. Cooking food, staying warm in winter, and cooling off with moving air all involve heat transfer.

When you understand conduction, convection, and radiation, you can explain how heat moves in the world around you.

Brief Summary

Heat moves from warmer things to cooler things. Conduction is heat by touching. Convection is heat carried by moving liquids and gases. Radiation is heat that travels by waves and does not need touching.

Electrical Energy and Simple Circuits

Have you ever turned on a flashlight, watched a toy car move, or seen a lamp light up? These things can work because of electrical energy. Electrical energy helps power many things we use every day.

In this lesson, you will learn what electrical energy is, what a circuit is, and why a circuit must be closed for electricity to make something work.

What is electrical energy?

Electrical energy is energy that moves through a path. It comes from tiny pieces of matter called electrons. You do not need to see electrons to understand that they move and carry energy.

When electrons move through the right kind of path, they can make a bulb glow, a buzzer buzz, or a small motor spin. That moving electrical energy can be changed into other kinds of energy, like light, sound, or motion.

What is a simple circuit?

A circuit is a path that electrical energy can follow. A simple circuit usually has these parts:

• Energy source such as a battery
• Wires to carry the electrical energy
• Device that uses the energy, such as a light bulb, buzzer, or motor
• Switch sometimes, to open or close the path

You can think of a circuit like a loop. The electrical energy must travel around the whole loop to make the device work.

Closed circuit and open circuit

A closed circuit is a complete, unbroken loop. In a closed circuit, electrical energy can move all the way around. When the loop is complete, the device can work.

An open circuit has a break or gap in the loop. If there is a break, the electrical energy cannot move through the whole path. Then the bulb will not light, the buzzer will not buzz, and the motor will not spin.

• Closed circuit = complete path = device works
• Open circuit = broken path = device does not work

What does a battery do?

A battery is an energy source. It provides the electrical energy for the circuit. Without a battery or another source of electrical energy, the circuit cannot power a device.

The battery pushes electrical energy through the wires and into the device. Then the device uses that energy to do a job.

What do wires do?

Wires connect the parts of a circuit. They give electrical energy a path to follow. The wires must be connected the right way so the path is complete.

If a wire is loose, missing, or broken, the circuit becomes open. Then the electrical energy cannot travel around the loop.

What does the device do?

The device in the circuit uses electrical energy and changes it into another form of energy.

• A light bulb changes electrical energy into light and a little heat.
• A buzzer changes electrical energy into sound.
• A motor changes electrical energy into motion.

This shows that energy can be transferred and changed from one form to another.

What does a switch do?

A switch controls whether the circuit is open or closed.

• When the switch is on, it usually closes the circuit.
• When the switch is off, it usually opens the circuit.

That is why flipping a switch can turn a light on or off.

How electrical energy moves in a circuit

In a simple circuit, the battery gives electrical energy. The energy moves through the wires, reaches the device, and then continues through the loop.

If the path is complete, the energy keeps moving through the whole circuit. If there is a gap anywhere, the movement stops.

You can imagine it like a train track in a circle. If part of the track is missing, the train cannot go all the way around. A circuit works the same way. It needs a full loop.

Important idea: the loop must be unbroken

The most important thing to remember is this: electrical energy needs a closed, unbroken loop.

Even if you have a battery, wires, and a bulb, the bulb will not light unless everything is connected in one complete path.

Worked Example 1: Will the bulb light?

A circuit has 1 battery, 2 wires, and 1 bulb. The wires connect the battery to the bulb on both sides. There are no gaps.

Step 1: Check for an energy source. Yes, there is a battery.

Step 2: Check for a complete loop. Yes, the wires connect everything with no breaks.

Step 3: Decide if the circuit is open or closed. It is closed.

Answer: Yes, the bulb will light.

Worked Example 2: Why does the buzzer not work?

A battery, wires, and a buzzer are connected, but one wire fell off the battery.

Step 1: Is there a battery? Yes.

Step 2: Is the loop complete? No, one wire is not connected.

Step 3: Is the circuit open or closed? It is open.

Answer: The buzzer does not work because the circuit has a break.

Worked Example 3: What happens when the switch changes?

A simple circuit has a battery, wires, a switch, and a lamp.

At first, the switch is off.

• The switch makes a gap in the path.
• The circuit is open.
• The lamp is off.

Then the switch is turned on.

• The gap is closed.
• The circuit is closed.
• The lamp turns on.

Answer: The switch controls whether electrical energy can travel through the loop.

Worked Example 4: What kind of energy change happens?

A toy with a small motor uses a battery to make its wheels turn.

Step 1: The battery provides electrical energy.

Step 2: The motor uses that energy.

Step 3: The wheels turn, so the energy changes into motion.

Answer: Electrical energy changes into motion energy.

Things to remember about simple circuits

1. A circuit is a path for electrical energy.
2. A simple circuit needs a source, like a battery.
3. Wires connect the parts of the circuit.
4. A device, like a bulb or buzzer, uses the energy.
5. The circuit must be closed, which means complete and unbroken.
6. If the circuit is open, the device will not work.

Look at the pattern

When the loop is complete, the device works. When the loop is broken, the device stops. We can write this idea like this:

Closed circuit \(\rightarrow\) works

Open circuit \(\rightarrow\) does not work

Real-life examples

• A flashlight works when its batteries are in place and the switch closes the circuit.
• A lamp turns on when the plug, wires, and bulb are connected and the switch closes the path.
• A battery-powered toy stops working if the battery is dead or a wire inside is loose.

Brief Summary

Electrical energy is the movement of electrons through a path. That path is called a circuit. A simple circuit needs a battery, wires, and a device, and it may also have a switch.

For the device to work, the circuit must be a closed, unbroken loop. If there is any gap, the circuit is open, and the electrical energy cannot make the device work.

Batteries and Stored Chemical Energy

Have you ever used a flashlight, a toy car, or a remote control? Many of these things need a battery to work. A battery may look small, but it does an important job.

A battery stores energy. The energy inside a battery is called chemical energy. When the battery is connected in a circuit, it changes that stored chemical energy into electrical energy. The electrical energy can then power things like lights, sounds, and motion.

In this lesson, you will learn what batteries do, what stored chemical energy means, and how a battery helps energy move from one place to another.

What is stored chemical energy?

Chemical energy is energy stored in materials. A battery has chemicals inside it. These chemicals hold energy, even when the battery is just sitting on a table.

This is called stored chemical energy because the energy is saved inside the battery until it is needed. The battery does not have to be moving or glowing to have energy. It already has energy stored inside.

You can think of a battery like a snack pack for a machine. Food stores energy for your body. A battery stores energy for a device.

What happens when a battery is used?

When a battery is placed in a device and the circuit is complete, the stored chemical energy begins to change into electrical energy. Electrical energy moves through the circuit.

A circuit is a path that electrical energy can travel through. If the path is complete, the energy can move. If the path is broken, the energy cannot move.

For example, in a flashlight:

• The battery stores chemical energy.
• The battery changes that energy into electrical energy.
• The electrical energy moves through the circuit.
• The bulb changes some of that energy into light and heat.

So the energy changes form, but it does not disappear. It starts as stored chemical energy in the battery and then becomes electrical energy, light, and heat.

Energy can change forms

Energy can be stored, moved, and changed from one form to another. A battery is a good example of this.

Here is a simple energy change:

chemical energy in a battery → electrical energy in a circuit → light, sound, motion, or heat

A battery might help:

• a flashlight make light
• a toy make sound
• a small fan make motion
• a device become a little warm

Energy is transferred

When we say energy is transferred, we mean it moves from one place to another or from one object to another. In a battery-powered device, energy is transferred from the battery to the device.

For example, a battery in a toy car transfers energy to the motor. The motor uses that energy to make the wheels turn.

Energy is conserved

An important science idea is that energy is conserved. That means energy is not made from nothing, and it does not vanish. It changes form or moves from place to place.

When a battery runs a flashlight, the energy does not disappear. It changes:

• from chemical energy in the battery
• to electrical energy in the circuit
• to light and heat in the bulb

What does it mean when a battery dies?

People often say a battery is "dead." This does not mean the battery was alive. It means the battery has used most of its stored chemical energy.

When the stored chemical energy is mostly gone, the battery cannot keep providing enough electrical energy to power the device.

The battery may still be in the device, but it cannot do its job well anymore.

Examples of batteries in everyday life

• flashlights
• remote controls
• toy cars
• clocks
• wireless game controllers
• some doorbells

All of these devices use batteries to provide energy. The battery is the source of stored chemical energy.

Worked Example 1: Flashlight

Question: A flashlight has working batteries in it. What kind of energy is stored in the batteries, and what does it change into when the flashlight is turned on?

Step 1: Think about what batteries store. Batteries store chemical energy.

Step 2: When the flashlight is turned on, the battery sends electrical energy through the circuit.

Step 3: The bulb changes that energy into light and some heat.

Answer: The batteries store chemical energy. When the flashlight is on, that energy changes into electrical energy, and then into light and heat.

Worked Example 2: Toy Car

Question: A toy car moves when batteries are inside it. How does the battery help the car move?

Step 1: The battery stores chemical energy.

Step 2: In a complete circuit, the battery changes that energy into electrical energy.

Step 3: The electrical energy goes to the motor.

Step 4: The motor changes the energy into motion so the wheels can turn.

Answer: The battery stores chemical energy and changes it into electrical energy. The toy car uses that energy to make motion.

Worked Example 3: Broken Circuit

Question: A battery is inside a lamp toy, but the toy does not light up. One wire is loose. Why does the toy not work?

Step 1: The battery still has stored chemical energy.

Step 2: But a loose wire means the circuit is broken.

Step 3: If the circuit is broken, electrical energy cannot move through the whole path.

Answer: The toy does not work because the circuit is broken. The battery can only power the toy when the path is complete.

Worked Example 4: Dead Battery

Question: A remote control worked yesterday, but today it does not. New batteries make it work again. What probably happened?

Step 1: The old batteries had stored chemical energy.

Step 2: Over time, that stored energy was used.

Step 3: When the stored chemical energy was mostly gone, the batteries could not provide enough electrical energy.

Answer: The old batteries used most of their stored chemical energy, so the remote needed new batteries.

Important ideas to remember

• A battery stores chemical energy.
• When connected in a complete circuit, a battery changes chemical energy into electrical energy.
• Electrical energy can be changed into light, sound, motion, or heat.
• Energy is transferred from the battery to the device.
• Energy is conserved, which means it changes form and does not just disappear.

Quick Check

1. What kind of energy is stored in a battery?
2. What must a circuit have for electrical energy to move?
3. What forms of energy might come from a battery-powered device?
4. What does it mean when a battery is "dead"?

Brief Summary

Batteries store chemical energy. When a battery is connected in a complete circuit, it changes that stored energy into electrical energy. The electrical energy can then become light, sound, motion, or heat in a device. The energy does not disappear—it changes form and is transferred from the battery to the device.