Forces, Motion, and Energy

Contact and Noncontact Forces

Things move when a force acts on them. A force is a push or a pull.

When you open a door, kick a ball, or pull a wagon, you are using force. Forces can make things start moving, stop moving, speed up, slow down, or change direction.

There are two main kinds of forces we will learn about today:

• Contact forces — forces that happen when things touch.
• Noncontact forces — forces that happen when things do not touch.

1. What is a contact force?

A contact force needs touch. If one object pushes or pulls another object by touching it, that is a contact force.

Here are some examples of contact forces:

• Pushing a toy car with your hand
• Pulling a sled with a rope
• Kicking a soccer ball
• Catching a ball with your hands

In each example, the objects are touching. That is why these are contact forces.

2. What is a noncontact force?

A noncontact force does not need touch. It can act over a distance.

That means one object can push or pull another object even when they are not touching.

Two important noncontact forces are:

• Gravity
• Magnetism

3. Gravity

Gravity is a force that pulls things downward toward Earth.

When you drop a pencil, gravity pulls it down. When rain falls from the clouds, gravity pulls it down too.

You do not have to touch the pencil to make it fall. Gravity is pulling on it, so gravity is a noncontact force.

4. Magnetism

Magnetism is a force made by magnets. A magnet can pull some metal objects, like paper clips, even before touching them.

Magnets can also push other magnets away. So magnetism can pull or push without touching first.

Because magnets can act from a distance, magnetism is a noncontact force.

5. How are contact and noncontact forces different?

• Contact force: needs touching
• Noncontact force: does not need touching

You can ask yourself this simple question:

“Do the objects have to touch for the force to happen?”

• If yes, it is a contact force.
• If no, it is a noncontact force.

6. Everyday examples

• You push a swing. Contact force
• A backpack falls off a chair. Noncontact force because of gravity
• You pull a drawer open. Contact force
• A magnet picks up a paper clip. Noncontact force

7. Worked Examples

Example 1: Pushing a toy car

A child puts a hand on a toy car and pushes it across the floor.

Question: Is this a contact force or a noncontact force?

Answer: It is a contact force.

Why? The hand is touching the toy car. The push happens because of touch.

Example 2: An apple falling from a tree

An apple drops from a tree and falls to the ground.

Question: Is this a contact force or a noncontact force?

Answer: It is a noncontact force.

Why? Gravity pulls the apple down, and gravity does not need touch.

Example 3: A magnet and a paper clip

A magnet is held close to a paper clip. The paper clip moves toward the magnet before they touch.

Question: Is this a contact force or a noncontact force?

Answer: It is a noncontact force.

Why? The magnet pulls the paper clip from a distance.

Example 4: Pulling a wagon

A child pulls a wagon using the handle.

Question: Is this a contact force or a noncontact force?

Answer: It is a contact force.

Why? The child is pulling the handle, and the handle is touching the wagon.

8. Let’s sort some forces

Here is a helpful way to sort them:

• Contact forces:
  • Pushing a chair
  • Pulling a kite string
  • Hitting a baseball with a bat
• Noncontact forces:
  • A ball falling
  • A magnet attracting a nail
  • Two magnets pushing apart

9. Important idea to remember

Sometimes more than one force can happen at the same time. For example, when you toss a ball up, your hand uses a contact force to push it. Then gravity, a noncontact force, pulls it back down.

This means an object can be affected by different forces during its motion.

10. Quick check

1. Does a contact force need touch? Yes.
2. Does gravity need touch? No.
3. Is magnetism a contact or noncontact force? Noncontact force.
4. Is kicking a ball a contact or noncontact force? Contact force.

Summary

A force is a push or a pull. Forces can make things move, stop, or change direction.

Contact forces happen when objects touch. Noncontact forces happen when objects do not touch.

Gravity and magnetism are noncontact forces. Pushing, pulling, kicking, and catching are contact forces.

If you can answer the question “Are the objects touching?”, you can often tell which kind of force it is.