Properties and States of Matter

Defining Matter

Have you ever looked around your room and seen toys, books, water, air, and your own hands? These are all examples of matter.

Matter is anything that has mass and takes up space.

That means if something is a thing you can hold, touch, pour, or feel, it is usually matter. Some matter is easy to see, like a rock. Some matter is hard to see, like air. But both are matter.

Let’s learn what makes something matter.

1. Matter takes up space

If something takes up space, it has a place where it is. A chair takes up space on the floor. A balloon takes up space in the air. Water takes up space in a cup.

Even air takes up space. If you blow up a balloon, the balloon gets bigger because the air inside it takes up space.

2. Matter has mass

Mass means how much “stuff” is in something. A big rock has mass. A tiny pebble has mass too. A feather has less mass than a rock, but it is still matter.

You do not have to measure mass with numbers to know something has mass. If it is made of “stuff,” then it has mass.

3. Matter can be solid, liquid, or gas

Matter can be in different forms called states.

• Solid: A solid keeps its shape. Examples: a book, a pencil, an apple.
• Liquid: A liquid can be poured and takes the shape of its cup or bowl. Examples: water, milk, juice.
• Gas: A gas spreads out and may be hard to see. Examples: air in a balloon, the air around us.

All three are matter because they have mass and take up space.

4. Some things are not matter

Not everything is matter. Some things do not take up space like objects do, and they are not made of “stuff.”

For example:

• Light is not matter.
• Sound is not matter.
• Heat is not matter.

You can see light, hear sound, and feel heat, but they are not matter.

How can we tell if something is matter?

Ask these two simple questions:

1. Does it take up space?
2. Does it have mass?

If the answer is yes to both, it is matter.

Examples of matter

• Your backpack
• A puddle of water
• A pet dog
• A cloud of air in a ball
• A sandwich

Examples of non-matter

• Sunlight
• A sound from a bell
• Heat from a stove

Worked Example 1

Question: Is a toy car matter?

Think: Does it take up space? Yes. Does it have mass? Yes.

Answer: Yes, a toy car is matter.

Worked Example 2

Question: Is water matter?

Think: Water fills a cup, so it takes up space. Water also has mass.

Answer: Yes, water is matter.

Worked Example 3

Question: Is air matter?

Think: Air may be hard to see, but it fills a balloon, so it takes up space. Air also has mass.

Answer: Yes, air is matter.

Worked Example 4

Question: Is light matter?

Think: Light helps us see, but it is not made of “stuff” like a chair or water. We do not say light takes up space like an object does.

Answer: No, light is not matter.

Let’s compare

• Rock: matter
• Milk: matter
• Air: matter
• Sound: not matter
• Light: not matter

Try this idea at home or school

Look around the room and name 3 things that are matter. Then name 1 thing that is not matter.

You might say:

• Desk = matter
• Crayon = matter
• Water bottle = matter
• Light from the lamp = not matter

Summary

Matter is anything that has mass and takes up space. Solids, liquids, and gases are all matter. Things like light, sound, and heat are not matter. When you want to decide if something is matter, ask: Does it take up space? Does it have mass?

Observable Physical Properties are things we can notice about an object by using our senses in a safe way.

We can look at an object, touch it, and sometimes smell it. These clues help us describe and sort materials.

Everything around us is made of matter. Matter is anything that takes up space. Different kinds of matter can look and feel different. These differences are called physical properties.

In this lesson, we will learn about six physical properties:

• color
• texture
• hardness
• flexibility
• luster
• odor

1. Color

Color is what we see with our eyes. An object can be red, blue, green, yellow, black, white, brown, or many other colors.

We can use color to describe and sort objects. For example, a banana is yellow, and grass is green.

2. Texture

Texture is how something feels when we touch it.

Some objects feel smooth, like a glass window. Some feel rough, like tree bark. Some feel soft, like a stuffed toy.

3. Hardness

Hardness tells if something feels hard or soft when we press it.

A rock is hard. A pillow is soft. Hard objects do not change shape easily when we push on them. Soft objects can squish more easily.

4. Flexibility

Flexibility tells if something can bend.

A rubber band is flexible because it bends and stretches. A wooden block is not very flexible because it does not bend easily.

5. Luster

Luster means how shiny something looks.

Some things are shiny, like a spoon. Some things are dull, which means not shiny, like a piece of cardboard.

6. Odor

Odor is how something smells.

A flower may have a sweet smell. A peeled onion may have a strong smell. We only smell things when a grown-up says it is safe.

Using Our Senses Safely

• We look with our eyes to see color and shininess.
• We touch with our hands to feel texture, hardness, and flexibility.
• We smell only if it is safe and a grown-up says yes.
• We do not taste objects in science class unless a teacher says it is okay.

Why do physical properties matter?

Physical properties help us tell objects apart. They also help us group things that are alike.

For example, if you have a metal spoon and a plastic spoon, you might notice that both are smooth. But the metal spoon is shinier.

We can describe one object in many ways.

An apple can be:

• red or green
• smooth
• firm, or a little hard
• not very bendy
• not shiny like metal
• sweet-smelling

That means one object can have many physical properties at the same time.

Worked Example 1: Describe a rock

Let us look at a rock and describe its properties.

1. Color: It might be gray or brown.
2. Texture: It may feel rough.
3. Hardness: It is hard.
4. Flexibility: It does not bend.
5. Luster: It is usually not very shiny.
6. Odor: It usually has little or no smell.

Answer: A rock can be gray, rough, hard, not bendy, dull, and have little odor.

Worked Example 2: Compare a spoon and a sponge

Now let us compare two objects.

Spoon:

• smooth
• hard
• not bendy
• shiny

Sponge:

• soft
• squishy
• can bend
• not shiny

Answer: The spoon and sponge are different because they have different texture, hardness, flexibility, and luster.

Worked Example 3: Sort objects by one property

Suppose we have these objects: a coin, a paper towel, a crayon, and a mirror.

Let us sort them by luster.

Shiny:

• coin
• mirror

Not shiny:

• paper towel
• crayon

Answer: We sorted the objects by looking at which ones are shiny and which ones are dull.

Worked Example 4: Find two objects that are alike and different

Think about a rubber ball and a wooden block.

Alike:

• Both can be smooth.
• Both may have color.

Different:

• The rubber ball is more flexible.
• The wooden block is less flexible.
• The wooden block feels harder.

Answer: Objects can be alike in some properties and different in others.

Helpful Questions to Ask

When you study an object, you can ask:

• What color is it?
• Does it feel smooth or rough?
• Is it hard or soft?
• Can it bend?
• Is it shiny or dull?
• Does it have a smell?

Let’s remember

Observable physical properties are things we can notice about objects. We use our eyes, hands, and sometimes our nose to learn about them safely.

These properties help us describe objects and sort them into groups. If two things look the same in one way, they may still be different in another way.

Brief Summary

Physical properties are what we can notice about matter. Color, texture, hardness, flexibility, luster, and odor help us describe objects. We can use these properties to compare and sort materials safely.

States of Matter: Solids

Everything around us is made of matter. Matter is anything that takes up space.

Matter can be different kinds, called states of matter. In this lesson, we will learn about one state of matter: solids.

A solid is a kind of matter that has a definite shape and a definite volume.

Definite shape means a solid keeps its own shape. A book stays book-shaped. A rock stays rock-shaped.

Definite volume means a solid takes up the same amount of space unless something changes it. A toy block does not spread out to fill a cup. It keeps the same size.

Solids keep their shape and volume because the tiny pieces inside them, called particles, are packed very close together.

These particles do not move around freely. They vibrate in place. That means they wiggle a tiny bit, but they stay in their spots.

Because the particles are tightly packed, solids are usually easy to hold. They do not pour like water, and they do not float around like air.

Let’s look at the main things to remember about solids.

• A solid has its own shape.
• A solid has its own size.
• The particles are close together.
• The particles vibrate in place.

We can see solids all around us every day.

• A chair is a solid.
• An ice cube is a solid.
• A pencil is a solid.
• A coin is a solid.
• An apple is a solid.

When you put a solid on a table, it does not change to match the table. It keeps its own shape.

For example, if you put a block in a box, the block does not become box-shaped. It stays a block. That is how we know it is a solid.

Some solids can be big, and some can be small. Some solids can be hard, and some can be soft. But they are still solids if they keep their own shape and size.

For example, a wooden cube is hard. A sponge can feel soft. Both are solids because both have a definite shape and definite volume.

Worked Example 1

Question: Is a rock a solid?

Think: Does it keep its own shape? Does it take up its own amount of space?

Answer: Yes, a rock is a solid.

Why: A rock keeps its shape, and it takes up space. Its particles are packed close together.

Worked Example 2

Question: You put a toy block into a bucket. Does the block change shape to fit the bucket?

Think: Solids keep their own shape.

Answer: No, the block does not change shape.

Why: A toy block is a solid, so it keeps its definite shape and definite volume.

Worked Example 3

Question: Which one is a solid: a pencil or juice?

Think: A solid keeps its own shape.

Answer: The pencil is a solid.

Why: A pencil keeps its shape. Juice does not keep its own shape.

Worked Example 4

Question: A sponge is soft. Can it still be a solid?

Think: Solids do not have to be hard. They need to keep their own shape and volume.

Answer: Yes, a sponge can still be a solid.

Why: Even though it feels soft, it is still matter with a definite shape and a definite volume.

Here is a simple way to check if something is a solid.

1. Look at the object.
2. Ask, “Does it keep its own shape?”
3. Ask, “Does it take up its own amount of space?”
4. If the answer is yes, it is probably a solid.

Let’s practice with a few more objects.

• A crayon keeps its shape, so it is a solid.
• A spoon keeps its shape, so it is a solid.
• A ball keeps its shape, so it is a solid.
• An eraser keeps its shape, so it is a solid.

Remember, solids can come in many shapes, colors, and sizes. What makes them solids is not their color or how big they are. What matters is that they keep their shape and volume.

Summary

A solid is a state of matter. Solids have a definite shape and a definite volume. This happens because their particles are tightly packed and vibrate in place. Rocks, books, pencils, apples, and blocks are all examples of solids.

Liquids Are a State of Matter

Everything around us is made of matter. Matter is anything that takes up space.

One kind of matter is called a liquid. Liquids are all around us every day.

We drink liquids like water and milk. We also see liquids like juice, soup, and rain.

What Makes a Liquid Special?

A liquid has its own amount, but it does not keep its own shape.

This means a liquid has a definite volume. That is a big science way to say the liquid stays the same amount unless some is added or taken away.

But a liquid changes shape to fit the container it is in. A container can be a cup, bowl, bottle, or bathtub.

Think About Water

If you pour water into a tall glass, the water becomes tall and narrow.

If you pour that same water into a wide bowl, the water becomes short and wide.

It is still the same amount of water. The shape changes, but the amount stays the same.

Liquids Can Flow

Liquids can flow. That means they can move and be poured.

When you tip a cup of juice, the juice flows out. When rain falls, water flows down. When you stir soup, the soup moves around the bowl.

Tiny Pieces in a Liquid

Liquids are made of very tiny pieces called particles.

In a liquid, the particles are close together, but they are not stuck tight. They can move past each other.

That is why liquids can flow and take the shape of their container.

How Are Liquids Different From Solids?

A solid keeps its own shape. A block, a book, and an ice cube are solids.

A liquid does not keep its own shape. Water, milk, and oil are liquids.

If you put a toy block in a cup, it still looks like a block. If you put water in a cup, it takes the shape of the cup.

Signs Something Is a Liquid

• It can be poured.
• It can flow.
• It takes the shape of its container.
• It keeps the same amount unless more is added or some is spilled.

Examples of Liquids

• Water
• Milk
• Juice
• Oil
• Soup
• Rain

Be Careful: Not Everything That Moves Is a Liquid

Sand and rice can be poured, but they are made of many tiny solids. Each grain keeps its own shape.

A true liquid does not have pieces you can easily see. It flows together and fits the container.

Worked Example 1

Question: Mia pours milk from a carton into a cup. What shape does the milk have?

Think: A liquid does not keep its own shape. It takes the shape of its container.

Answer: The milk has the shape of the cup.

Worked Example 2

Question: Ben has a bowl with water. He pours the same water into a bottle. Is it still the same amount of water?

Think: A liquid can change shape, but the amount stays the same if none is added or spilled.

Answer: Yes, it is the same amount of water. Only the shape changed.

Worked Example 3

Question: Which one is a liquid: a pencil, apple juice, or a rock?

Think: A liquid can flow and take the shape of its container.

Answer: Apple juice is a liquid.

Worked Example 4

Question: Ava says, “Water in a glass and water in a bowl are different because they have different shapes.” Is Ava right?

Think: Liquids change shape to match the container.

Answer: Ava is not right. The water can have different shapes in different containers, but it is still a liquid.

Let’s Remember

1. A liquid is a kind of matter.
2. A liquid has a definite amount.
3. A liquid does not keep its own shape.
4. A liquid takes the shape of its container.
5. A liquid can flow and be poured.

Quick Check

• Does water keep its own shape? No.
• Can juice be poured? Yes.
• Does milk in a bottle and milk in a bowl stay the same amount if none spills? Yes.
• Is a rock a liquid? No.

Summary

Liquids are a state of matter. They have a definite amount, but they do not keep their own shape.

Liquids flow and take the shape of their container. Water, milk, and juice are all examples of liquids.

States of Matter: Gases

Everything around us is made of matter. Matter is anything that takes up space.

Matter can be different in different ways. One way is called its state. Today we will learn about the state called gas.

A gas is a kind of matter that does not have its own shape. It does not have its own size of space, either. A gas spreads out and fills the space around it.

That means a gas can be in a small place or a big place. It changes to fit the space it is in.

Air is the best example of a gas. We cannot usually see air, but it is all around us. It takes up space, even though it is hard to see.

We can learn about gases by watching what air does.

Main Ideas About Gases

• A gas has no shape of its own.
• A gas has no set amount of space of its own.
• A gas spreads out to fill the space it is in.
• Air is a gas.

If you blow air into a balloon, the air fills the balloon. The balloon changes shape because the air inside spreads out.

If you blow more air into the balloon, it gets bigger. This shows that gas can fill more space.

If air is in a room, it spreads through the room. It does not stay in one little corner. It fills the space that is open to it.

Even though we cannot see most gases, we can see their effects. We can feel air when wind blows. We can see a balloon puff up. We can hear air coming out with a hiss.

How Gases Are Different

A chair keeps the same shape. A cup of juice takes the shape of its cup. But a gas does something different. A gas spreads out to fill all the space it can.

So, a gas does not have a shape of its own, and it does not have a set size of space of its own.

Places We Find Gases

• the air in a room
• the air inside a balloon
• the wind outside
• air in a tire

Worked Example 1

Question: Is air a gas?

Think: A gas does not have its own shape and spreads out to fill space. Air does this.

Answer: Yes. Air is a gas.

Worked Example 2

Question: A balloon is empty. Then you blow air into it. What happens to the balloon?

Think: The air is a gas. Gas takes up space and fills the space inside the balloon.

Answer: The balloon gets bigger because the air fills it.

Worked Example 3

Question: Does a gas have its own shape?

Think: Gas changes to fit the place it is in.

Answer: No. A gas does not have its own shape.

Worked Example 4

Question: If air is put into a big ball and a small ball, will it stay the same shape in both?

Think: Gas does not keep one shape. It fills the space it is in.

Answer: No. The air will fit the shape and size of each ball.

Try to Remember

1. A gas is matter.
2. A gas has no definite shape.
3. A gas has no definite volume, which means no set amount of space of its own.
4. A gas fills the space it is in.
5. Air is a gas.

Quick Check

• Can you usually see air? No
• Is air still matter? Yes
• Does a gas have its own shape? No
• Does a gas fill the space around it? Yes

Summary

Gases are a state of matter. A gas does not have its own shape, and it does not have its own set amount of space. A gas spreads out to fill the space it is in. Air is a gas, and a balloon is a great way to see that gas takes up space.

Thermal Phase Changes: Melting and Freezing

Everything around us is made of matter. Matter can be a solid or a liquid.

A solid keeps its own shape. An ice cube is a solid. A rock is a solid.

A liquid can flow and take the shape of its cup or bowl. Water and juice are liquids.

Sometimes matter changes from one state to another. Today we will learn about two changes: melting and freezing.

Melting happens when a solid gets warmer and changes into a liquid.

Freezing happens when a liquid gets cooler and changes into a solid.

We can say it like this:

• Add heat  solid melts into a liquid
• Take away heat  liquid freezes into a solid

Heat is thermal energy. When something gets heat, it gets warmer. When heat is taken away, it gets cooler.

Melting is easy to see with ice. Ice is solid water. When ice sits in a warm room, it gets heat. The ice melts and turns into liquid water.

Freezing is easy to see with water. When water is put in a freezer, heat is taken away. The water freezes and turns into solid ice.

These are physical changes. That means the matter is still the same thing. Ice and water are both water. Melted chocolate and hard chocolate are both chocolate.

Let us look at some clues to help us know what is happening.

• If something was hard and becomes runny, it is probably melting.
• If something was runny and becomes hard, it is probably freezing.
• If heat is added, melting may happen.
• If heat is removed, freezing may happen.

Examples from everyday life

• An ice pop left in the sun melts.
• Butter in a warm pan melts.
• Water in an ice tray in the freezer freezes.
• Juice can freeze and become a popsicle.

Worked Example 1

You put an ice cube on a plate. After a while, there is a little puddle of water.

What happened?

The ice cube got heat from the room. The solid ice changed into liquid water. That is called melting.

Worked Example 2

You pour water into an ice tray and put it in the freezer. Later, the water is hard ice.

What happened?

Heat was taken away from the water in the freezer. The liquid water changed into solid ice. That is called freezing.

Worked Example 3

A stick of butter is left near a warm stove. It gets soft and starts to look runny.

Is it melting or freezing?

It is melting. The butter is getting warmer. A solid is changing into a liquid.

Worked Example 4

Juice is poured into a popsicle mold and put into the freezer. Later, it is hard and icy.

Is it melting or freezing?

It is freezing. The juice is losing heat. A liquid is changing into a solid.

Let us compare melting and freezing

• Melting: solid  liquid
• Freezing: liquid  solid
• Melting: heat is added
• Freezing: heat is taken away

We can show the changes like this:

Solid \(\rightarrow\) Liquid

Liquid \(\rightarrow\) Solid

Here is one more way to think about it:

1. Touch is not always safe, so we look carefully.
2. If something becomes more loose and watery, it may be melting.
3. If something becomes firm and hard, it may be freezing.

Important idea: Melting and freezing can happen again and again. Ice can melt into water. Then water can freeze back into ice.

That means the change can go back and forth:

Ice \(\rightarrow\) Water \(\rightarrow\) Ice

Brief Summary

Matter can be a solid or a liquid. Melting is when heat is added and a solid changes into a liquid. Freezing is when heat is taken away and a liquid changes into a solid. Ice melting into water and water freezing into ice are great examples of these changes.

Thermal Phase Changes: Evaporation and Condensation

Everything around us is made of matter. Matter can be a solid, a liquid, or a gas.

In this lesson, we will learn about two ways matter can change: evaporation and condensation.

These changes happen when matter gets warmer or cooler. A liquid can change into a gas, and a gas can change back into a liquid.

What Is Evaporation?

Evaporation is when a liquid changes into a gas.

This happens when the liquid gets warm. Heat from the sun, warm air, or something hot can help a liquid evaporate.

Have you ever seen a puddle after it rains? Later, the puddle gets smaller and smaller. The water did not disappear. It changed into water vapor, a gas in the air. That is evaporation.

Wet clothes on a line can dry in the sun. The water in the clothes warms up and changes into a gas. This is another example of evaporation.

• A liquid starts the change.
• The liquid gets warm.
• It changes into a gas.

What Is Condensation?

Condensation is when a gas changes into a liquid.

This happens when the gas gets cool. When water vapor in the air touches something cold, it can turn into tiny drops of liquid water.

Think about a cold cup of water on a warm day. After a little while, small drops of water form on the outside of the cup. That water came from the air. The water vapor in the air cooled down and turned into liquid water. That is condensation.

You may also see drops on a bathroom mirror after a hot shower. Warm water makes water vapor. When the vapor touches the cooler mirror, it turns back into liquid drops. That is condensation.

• A gas starts the change.
• The gas gets cool.
• It changes into a liquid.

Evaporation and Condensation Are Opposites

Evaporation and condensation are opposite changes.

• Evaporation: liquid r gas
• Condensation: gas r liquid

We can show it like this:

$$\text{liquid} \rightarrow \text{gas}$$

$$\text{gas} \rightarrow \text{liquid}$$

When heat is added, a liquid can evaporate. When cooling happens, a gas can condense.

Why These Changes Matter

These changes happen all around us every day.

• Puddles dry because of evaporation.
• Wet hair dries because of evaporation.
• Water drops on a cold can happen because of condensation.
• Foggy windows can happen because of condensation.

Water can change from liquid to gas and back again. Even when it changes, it is still water.

Worked Example 1

Question: A puddle is on the sidewalk. The sun comes out, and later the puddle is gone. What happened?

Step 1: Start with what we see. The puddle is liquid water.

Step 2: The sun warms the water.

Step 3: Warm liquid water changes into a gas in the air.

Answer: This is evaporation.

Worked Example 2

Question: Tiny drops form on the outside of a cold juice box. What happened?

Step 1: The juice box is cold.

Step 2: Water vapor in the air touches the cold outside.

Step 3: The gas cools and turns into liquid drops.

Answer: This is condensation.

Worked Example 3

Question: Sam hangs a wet shirt outside. After some time, the shirt is dry. Is this evaporation or condensation?

Step 1: The shirt has liquid water in it.

Step 2: The air and sun help warm the water.

Step 3: The liquid water changes into gas and leaves the shirt.

Answer: This is evaporation.

Worked Example 4

Question: After a hot shower, Mia sees little drops on the mirror. Is this evaporation or condensation?

Step 1: The hot shower makes water vapor, which is a gas.

Step 2: The mirror is cooler than the warm air.

Step 3: The gas touches the cool mirror and turns into liquid drops.

Answer: This is condensation.

Let’s Remember

1. Evaporation means a liquid changes into a gas.
2. Condensation means a gas changes into a liquid.
3. Warming can cause evaporation.
4. Cooling can cause condensation.

A good way to think about it is this:

• If water dries up, it is usually evaporation.
• If water forms as drops, it is usually condensation.

Brief Summary

Evaporation happens when a liquid gets warm and changes into a gas. Condensation happens when a gas gets cool and changes into a liquid. We can see these changes in puddles, wet clothes, cold cups, and bathroom mirrors every day.

Material Permeability and Porosity

Everything around us is made of matter. Some things are hard, some are soft, and some can hold water better than others.

Today we will learn about how materials act when water touches them. Some materials soak up water. Some materials do not let water pass through.

This helps us choose the right material for different jobs. For example, we want a towel to soak up water. We want a raincoat to keep water out.

What do these words mean?

• Material: what something is made of, like paper, cloth, plastic, or wood.
• Permeable: lets water go into or through it.
• Impermeable or waterproof: does not let water go through it.
• Porous: has tiny little holes that can hold water.

If a material has many tiny holes, water can move into those holes. That material is often porous and permeable.

If a material has very few holes, or no holes that water can use, water stays on the outside. That material is often impermeable.

Think about a sponge. A sponge has many tiny spaces inside it. When water touches it, the sponge drinks up the water. That means the sponge is porous and permeable.

Think about plastic. When water lands on plastic, it usually makes drops and stays on top. The water does not soak in. That means plastic is usually impermeable.

How can we test a material?

We can do a simple water test. Put a few drops of water on a material and watch what happens.

1. Choose a material, like paper, cloth, foil, or plastic.
2. Put a small drop of water on it.
3. Look closely.
4. Ask: Did the water soak in? Did it stay on top? Did it go through?

If the water soaks in, the material is permeable. If the water stays on top and does not go through, the material is impermeable.

Why do some materials soak up water?

Some materials have tiny spaces inside them. Water can move into those spaces. That is why paper towels, tissues, and sponges can soak up spills.

Why do some materials keep water out?

Some materials have smooth surfaces and do not have spaces for water to move through. That is why rain boots, umbrellas, and plastic bags help keep things dry.

Examples from everyday life

• Towel: permeable, because it soaks up water.
• Sponge: porous and permeable, because it holds lots of water.
• Paper towel: permeable, because water soaks in fast.
• Plastic cup: impermeable, because water stays inside and does not leak through the sides.
• Raincoat: waterproof, because it keeps rain out.
• Foil: impermeable, because water does not soak through it.

Worked Example 1

You put one drop of water on a paper towel. The drop disappears into the paper towel.

Question: Is the paper towel permeable or impermeable?

Answer: The paper towel is permeable.

Why? The water soaked in. That means the paper towel lets water go into it.

Worked Example 2

You put one drop of water on a plastic lid. The drop stays on top and rolls around.

Question: Is the plastic lid permeable or impermeable?

Answer: The plastic lid is impermeable.

Why? The water did not soak in. It stayed on the outside.

Worked Example 3

You want to clean up spilled juice on the table. You can choose a sponge or a plastic sheet.

Question: Which one should you use?

Answer: You should use the sponge.

Why? A sponge is porous and permeable, so it can soak up the juice. A plastic sheet will not soak it up.

Worked Example 4

It is raining outside. You can wear a cotton shirt or a raincoat.

Question: Which one will help keep you dry?

Answer: The raincoat will help keep you dry.

Why? A raincoat is waterproof, so rain does not pass through it easily. A cotton shirt can soak up water.

Let’s compare materials

• If a material soaks up water, it is usually permeable.
• If a material has tiny holes, it is porous.
• If a material keeps water out, it is impermeable or waterproof.

Quick check

Ask yourself these questions when you test a material:

• Did the water soak in?
• Did the water stay on top?
• Would this material be good for drying spills?
• Would this material be good for keeping rain out?

Remember

Not all materials do the same job. Some are best for absorbing water. Some are best for blocking water.

When we know if a material is permeable, porous, or impermeable, we can choose the best one for what we need.

Summary

Materials can act differently with water. Permeable materials let water go in or through. Porous materials have tiny holes that can hold water. Impermeable or waterproof materials keep water out.

A sponge, towel, and paper towel are good at soaking up water. Plastic, foil, and raincoats are good at stopping water. We can test materials by putting a little water on them and watching what happens.

Optical Properties of Matter

Everything around us is made of matter. Matter is the "stuff" things are made of.

Some kinds of matter let light go through. Some let only a little light through. Some do not let light through at all.

When we learn how materials act with light, we are learning about their optical properties.

In this lesson, we will learn three important words:

• Transparent
• Translucent
• Opaque

These words help us describe what happens when light shines on an object.

1. Transparent

A material is transparent when light passes through it easily.

If something is transparent, you can usually see clearly through it.

Clear glass in a window is transparent. Clean water is transparent. Some plastic wrap is transparent too.

• Light goes through
• You can see clearly
• Examples: clear window, clear bottle, clean water

2. Translucent

A material is translucent when some light passes through, but not all of it in a clear way.

If something is translucent, you may see light and shapes, but they look blurry.

Wax paper is translucent. Frosted glass is translucent. A thin tissue paper can also be translucent.

• Some light goes through
• You cannot see clearly
• Things look blurry
• Examples: wax paper, frosted window, tissue paper

3. Opaque

A material is opaque when light is blocked.

If something is opaque, you cannot see through it.

A wooden door is opaque. A brick wall is opaque. A book is opaque too.

• Light does not go through
• You cannot see through it
• Examples: door, wall, book, metal pan

How to Tell the Difference

You can test a material by putting it in front of a light or in front of your eyes.

1. If you can see clearly through it, it is transparent.
2. If light comes through but the picture looks blurry, it is translucent.
3. If no light comes through and you cannot see through it, it is opaque.

Think About a Flashlight

Imagine shining a flashlight at three different objects.

• A clear plastic sheet: lots of light goes through. This is transparent.
• Wax paper: some light goes through, but it spreads out and looks fuzzy. This is translucent.
• A piece of cardboard: the light is blocked. This is opaque.

Why This Matters

We use different materials for different jobs.

• We use transparent glass in windows so we can see outside.
• We use translucent shower doors or lampshades when we want light, but not a clear view.
• We use opaque walls and doors for privacy and shade.

Worked Example 1

Question: Mia looks through a clean window and sees the playground clearly. Is the window transparent, translucent, or opaque?

Step 1: Ask, "Can Mia see clearly through it?"

Yes, she can.

Answer: The window is transparent.

Worked Example 2

Question: Ben shines a flashlight through wax paper. He sees light on the wall, but the light looks blurry. Is the wax paper transparent, translucent, or opaque?

Step 1: Ask, "Does some light go through?"

Yes.

Step 2: Ask, "Can Ben see clearly through it?"

No. The light looks blurry.

Answer: The wax paper is translucent.

Worked Example 3

Question: Ana puts a book in front of a flashlight. No light gets through. Is the book transparent, translucent, or opaque?

Step 1: Ask, "Does light go through the book?"

No.

Answer: The book is opaque.

Worked Example 4

Question: Look at these three objects: a clear cup, a frosted window, and a wooden block. Put them in the correct groups.

Step 1: The clear cup can be seen through clearly.

That means it is transparent.

Step 2: The frosted window lets in light, but you cannot see clearly through it.

That means it is translucent.

Step 3: The wooden block blocks light.

That means it is opaque.

Answers:

• Clear cup: transparent
• Frosted window: translucent
• Wooden block: opaque

Helpful Clues

• Transparent = see through clearly
• Translucent = light through, but blurry
• Opaque = blocks light

Try to Remember

Ask yourself these simple questions:

1. Can I see clearly through it?
2. Can I only see a blurry shape through it?
3. Can I not see through it at all?

The answers will help you choose the right word.

Summary

Materials interact with light in different ways. Transparent materials let light pass through so you can see clearly. Translucent materials let some light through, but images look blurry. Opaque materials block light, so you cannot see through them.

Magnetic Attraction and Repulsion

Magnets are special objects that can pull some things toward them. This pulling is called attraction.

Magnets can also push away other magnets. This pushing away is called repulsion.

In this lesson, we will learn:

• what a magnet does,
• what kinds of things magnets attract,
• what kinds of things magnets do not attract, and
• how magnets can pull and push.

What is a magnet?

A magnet is an object that has a magnetic force. We cannot see this force, but we can see what it does.

For example, a magnet can pick up a paper clip or make it move. That means the magnet is pulling on it.

Attraction means pull

When a magnet pulls something closer, that is called magnetic attraction.

Magnets attract some metals, such as iron and nickel. Many objects made with iron, like some nails and paper clips, can be attracted to a magnet.

Here are some things a magnet may attract:

• paper clips
• some nails
• some cans
• some metal toys

Not every metal is magnetic

This is very important: not all metals stick to magnets.

Some materials are not attracted to magnets, such as:

• wood
• plastic
• paper
• cloth
• glass
• aluminum

If a magnet does not pull an object, that means the object is not magnetic.

Repulsion means push away

Magnets do not only pull. Sometimes magnets push away.

When two magnets push apart, that is called magnetic repulsion.

You can feel this if you try to push two magnets together and they seem to say, “No!” They move away from each other.

Magnets can pull and push

A magnet can:

• pull some objects made of iron or nickel,
• pull another magnet, or
• push another magnet away.

So magnets can cause both attraction and repulsion.

How can we tell if something is magnetic?

We can test it with a magnet.

1. Pick an object.
2. Bring a magnet close to it.
3. Watch what happens.

If the object moves toward the magnet or sticks to it, it is magnetic.

If nothing happens, it is not magnetic.

Worked Example 1

Mia has a magnet and a paper clip.

She brings the magnet close to the paper clip. The paper clip jumps to the magnet.

What happened?

• The magnet attracted the paper clip.
• The paper clip is made from a metal the magnet can pull.

Answer: This is magnetic attraction.

Worked Example 2

Leo tries a magnet on a wooden block.

The wooden block does not move at all.

What happened?

• The magnet did not attract the wood.
• Wood is not magnetic.

Answer: The magnet has no effect on the wooden block.

Worked Example 3

Ava holds two magnets.

She tries to push them together, but they push away from each other.

What happened?

• The two magnets are repelling.
• Repulsion means push away.

Answer: This is magnetic repulsion.

Worked Example 4

Noah tests four objects with a magnet:

• a plastic spoon
• a paper clip
• a piece of aluminum foil
• a wooden stick

Only one object sticks to the magnet.

Which object is it?

Let us think:

• plastic spoon: not magnetic
• paper clip: often magnetic
• aluminum foil: not magnetic
• wooden stick: not magnetic

Answer: The paper clip sticks to the magnet.

Things to remember

• Attract means pull closer.
• Repel means push away.
• Magnets attract some metals, like iron and nickel.
• Magnets do not attract materials like wood, plastic, or aluminum.
• Magnets can attract some objects and repel other magnets.

Quick Check

• If a magnet pulls a nail, is that attraction or repulsion?
• If two magnets push apart, is that attraction or repulsion?
• Will a magnet pull a plastic cup?
• Will a magnet pull some objects made of iron?

Answers:

• A magnet pulling a nail is attraction.
• Two magnets pushing apart is repulsion.
• No, a magnet will not pull a plastic cup.
• Yes, a magnet can pull some objects made of iron.

Summary

Magnets are special because they can pull some things and push some things. When a magnet pulls, that is called attraction. When magnets push away, that is called repulsion.

Magnets attract some metals like iron and nickel, but they do not attract wood, plastic, paper, or aluminum. We can test objects with a magnet to see if they are magnetic.

Reversible Physical Changes

Everything around us is made of matter. Matter is "stuff" that takes up space. A toy, an ice cube, a book, and water are all matter.

Sometimes matter can change. Some changes only change how something looks, feels, or what state it is in. The matter is still the same kind of thing. This is called a physical change.

A reversible physical change is a change that can be changed back. That means the object or material can return to how it was before.

For example, if you freeze water into ice, it changes from a liquid to a solid. But it is still water. If the ice melts, it turns back into liquid water. That is a reversible physical change.

Main Idea: In a reversible physical change, the material stays the same, and the change can be undone.

Let’s learn some ways matter can change.

• Folding: A piece of paper can be folded and then unfolded.
• Freezing: Water can freeze into ice.
• Melting: Ice can melt into water.
• Stretching: A rubber band can be stretched and go back.

These are reversible because they can go back to the way they were before.

States of matter are ways matter can be. In 1st grade, we learn about:

• Solid: keeps its shape, like ice or a rock
• Liquid: flows, like water or juice

When water freezes, it changes from a liquid to a solid.

When ice melts, it changes from a solid to a liquid.

The material is still water both times. Only the state changes.

How do we know a change is reversible?

1. Ask: Is it still the same material?
2. Ask: Can it change back?

If the answer is yes, it is probably a reversible physical change.

Worked Example 1

A child folds a paper in half.

Question: Is this a reversible physical change?

Think: The paper is still paper. It only changed shape. The paper can be unfolded.

Answer: Yes. Folding paper is a reversible physical change.

Worked Example 2

Water is put in a freezer and becomes ice.

Question: Is this a reversible physical change?

Think: The water changed state. It went from liquid to solid. But it is still water. Ice can melt back into water.

Answer: Yes. Freezing water is a reversible physical change.

Worked Example 3

An ice cube sits on a plate and melts.

Question: Is this a reversible physical change?

Think: The ice changed from solid to liquid. But it is still water. The water can be frozen again.

Answer: Yes. Melting ice is a reversible physical change.

Worked Example 4

A rubber band is stretched and then let go.

Question: Is this a reversible physical change?

Think: The rubber band is still a rubber band. It changes shape for a little while and then goes back.

Answer: Yes. Stretching a rubber band is a reversible physical change.

Let’s compare changes.

If something can go back, it is reversible.

If something cannot go back easily, it is not reversible.

Here are some examples.

• Folded paper that can unfold: reversible
• Ice melting into water: reversible
• Water freezing into ice: reversible
• Rubber band stretching and going back: reversible

Be careful: Some actions change how something looks, but they may not go back easily. To be reversible, the material must still be the same and be able to return to its earlier form.

Try thinking like a scientist.

• What changed?
• Is it still the same material?
• Can it go back?

These questions help us decide if a change is a reversible physical change.

Quick Check

1. Ice turns into water. Can it go back to ice? Yes.

2. A paper is folded, then unfolded. Is it still paper? Yes.

3. A rubber band is stretched and then goes back. Did it stay the same material? Yes.

All of these are reversible physical changes.

Summary

A reversible physical change changes how matter looks, feels, or what state it is in, but the matter stays the same kind of material.

Water can freeze into ice and melt back into water. Paper can be folded and unfolded. A rubber band can stretch and go back.

When you want to know if a change is reversible, ask: Is it still the same material? and Can it change back?