Grade by Grade
C. Matter and Energy · Forces Causing Movement

What Is a Force? Contact and Non-Contact Forces

C2.1 A1.5About 30 minutes
Learning goals
  • I can explain that a force is a push or a pull.
  • I can tell the difference between a contact force and a non-contact force.
  • I can name examples of contact forces (like a push from my hand, friction and buoyancy) and non-contact forces (gravity, magnetism and static electricity).
  • I can use science words to share what I found out.

Words to know

force
A push or a pull on an object.
contact force
A force that only works when two things are touching, like your hand pushing a door.
non-contact force
A force that can push or pull from a distance, without touching, like a magnet pulling a paper clip.
gravity
The non-contact force that pulls things toward the Earth.
magnetism
The non-contact force of a magnet. It pulls on some metals, like iron and steel.
static electricity
A non-contact force made when some things are rubbed together, like a balloon rubbed on your hair.
friction
A contact force made when two surfaces rub. It slows things down.
buoyancy
A contact force from water (or another liquid) that pushes up on things in it.

Remember from Grade 2

In Grade 2 you learned that a force is a push or a pull. A push moves something away from you. A pull moves something toward you. You learned that gravity pulls things down when you drop them, and that rubbing makes friction. In Grade 3 you will become a force detective. You will learn about many kinds of forces and how they make things move.

A mystery at the rink

At the hockey rink, a player swings her stick. The stick hits the puck, and the puck shoots across the ice. The stick touched the puck, so it is easy to see what moved it.

After the game, she drops her mitten. Nothing touches the mitten, but it falls to the floor anyway. What pulled it down?

The answer is a force that does not need to touch: gravity. Today you will learn that there are two big families of forces.

A wooden hockey stick hitting a black puck on an indoor ice rink, with ice chips spraying.
The stick touches the puck to push it, so this is a contact force. Notice the spray of ice where the stick hits. AI-generated image

Two families of forces

Contact forces only work when two things touch.

  • Your hand pushing a door or pulling a wagon.
  • Friction: a sled rubbing on snow slows down.
  • Buoyancy: water pushing up on a canoe so it floats.

Non-contact forces can push or pull from a distance, with a gap in between.

  • Gravity pulls a falling maple leaf down to the ground.
  • Magnetism: a magnet pulls a paper clip, even before it touches it.
  • Static electricity: a balloon rubbed on your hair can pull your hair up, even before it touches.
boxpushcontact: touchingmagnetclippullnon-contact: a gap
Left: a hand pushes a box. They touch, so it is a contact force. Right: a magnet pulls a paper clip across a gap. They do not touch, so it is a non-contact force.
ForceContact or non-contact?Example
push or pull from a personcontactpushing a friend on a swing
frictioncontacta sled slowing down on snow
buoyancycontactwater holding up a canoe
gravitynon-contacta maple leaf falling to the ground
magnetismnon-contacta fridge magnet pulling on the fridge door
static electricitynon-contacta rubbed balloon pulling your hair up
Contact and non-contact forces
CONTACTthe things must touchNON-CONTACTworks across a gappush or pullfrictionbuoyancygravityNSmagnetismstaticelectricity
The six forces sorted. Contact forces only work when things touch. Non-contact forces work across a gap.

The touching test

Ask yourself: "Do the two things have to touch for the force to work?"

  • Yes → it is a contact force.
  • No, it can work across a gap → it is a non-contact force.
Worked example

Let's sort some forces

Sort each force: contact or non-contact?

  1. A dog pulls a sled with a rope.
  2. An apple falls from a tree.
  3. A magnet picks up a steel nail from a few centimetres away.
  4. Your boots grip the snowy sidewalk so you don't slip.
  1. Dog and sled: the dog pulls the rope and the rope pulls the sled. They are all joined and touching. Contact.
  2. Apple: nothing touches the apple as it falls. Gravity pulls it from a distance. Non-contact.
  3. Magnet and nail: the nail jumps toward the magnet across a gap. Non-contact (magnetism).
  4. Boots on snow: the bottoms of the boots rub on the sidewalk. That rubbing force is friction. Contact.

Contact: the dog and sled, the boots (friction). Non-contact: the apple (gravity), the magnet and nail (magnetism).

Science talk

Scientists share what they find using science words. Instead of "the thing made it go", try: "The magnet pulled the paper clip. It is a non-contact force because there was a gap."

Just for fun

What did the hockey puck say to the stick?

"Hey, there's no need to get so pushy!"

Hands-on activity

Force detective hunt

You need: paper, a pencil and a fridge magnet.

  1. Draw a line down the middle of your paper. Write Contact on one side and Non-contact on the other.
  2. Walk around your home. Look for forces in action: opening a drawer, a fridge magnet, a towel hanging down, a ball rolling and stopping.
  3. Try some yourself: drop a sock (what pulls it?), hold a fridge magnet near the fridge door and feel it pull before it touches, push a chair.
  4. Write or draw each force on the correct side. Try to find 5 contact forces and 3 non-contact forces.
  5. Share: explain two of your finds to a grown-up using the words force, contact and non-contact.

What to look for: pushes, pulls and rubbing go under contact; things falling (gravity) and magnets go under non-contact.

Safety: keep magnets away from screens and bank cards. Small magnets are not toys for little brothers and sisters: swallowing them is very dangerous.

Your turn

1

What is a force?

2

Is kicking a soccer ball a contact force or a non-contact force?

3

A snowflake falls from the sky. Which force pulls it down? Is it contact or non-contact?

4

Name the three non-contact forces you learned about today.

5

A canoe floats on a lake. Which force pushes it up?

6

You rub your hands together and they get warm. Which force is that?

7

Give one example of a contact force from your own day.

More practice: warm-up

1

Is pulling a wagon a push or a pull?

2

Does a contact force need the two things to touch?

3

Is gravity a contact force or a non-contact force?

4

What kind of force does a fridge magnet use?

5

Is a hockey stick hitting a puck a contact force?

More practice: on your own

1

A magnet pulls a paper clip that is 2 cm away. Why is this a non-contact force?

2

Sort these: a balloon rubbed on hair pulls the hair up; a girl pushes a shopping cart.

3

Why does a sled slow down and stop at the bottom of a hill?

4

Your friend says "Gravity only works when you touch the ground." Is that right? Explain.

5

Name one contact force and one non-contact force you could see at a winter playground.

Challenge

1

A child holds a magnet under a thin wooden table. A paper clip on top of the table slides along when the magnet moves. Which force is moving the clip? How do you know it is non-contact?

2

A tow truck pulls a car with a chain. Is that a contact force or a non-contact force? Explain.

3

Think of a ball thrown up into the air. Name one contact force and one non-contact force that act on it.

Check your understanding

Quiz

1.

A force is...

2.

Which is a non-contact force?

3.

Which is a contact force?

4.

Which force pushes up on a boat so it floats?

5.

What is the best test for a contact force?

6.

A balloon rubbed on your hair pulls your hair up. Which force is this?

For parents and teachers

Big idea: Forces are pushes and pulls. Ontario's Grade 3 science (C2.1) asks children to describe contact forces (forces that need touching, such as an applied push or pull, friction and buoyancy) and non-contact forces (forces that act across a distance: gravity, magnetism and static electricity). The next four lessons look at each force in more detail. Sharing findings with science words is part of the STEM skills in Strand A (A1.5).

How to help: Play "Name that force" during everyday moments: "Your spoon fell. What pulled it?" "Is that a contact or a non-contact force?" Use the touching test.

Common difficulties:

  • Thinking gravity only works on the ground. Point out that a thrown ball curves back down while it is still in the air.
  • Calling friction non-contact. Friction only happens where two surfaces rub, so it is contact.
  • Calling a rope pull non-contact because the person isn't touching the sled. The rope is touching both, so the pull passes through touching things.

Safety: small, strong magnets can cause serious injury if swallowed, especially by younger children. Store them out of reach.