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Lesson 04 – The Force of Friction

Read About Friction


Read the vocabulary terms to understand the reading better.


A force is the push or pull on an object that makes it move.


Friction is a force created when things rub against each other.


Movement means changing place or position.

What Is Friction?

Friction is a force. Friction is created when things rub against each other. What does friction do? Friction slows objects down.

Imagine you push a box across a smooth floor. The box moves then stops. The box and the floor rub against each other. There is friction between the floor and the box. Friction works against movement. Friction makes moving objects slow down.

Smooth and Rough Surfaces

When objects rub against each other, their surfaces touch. Rough surfaces create more friction than smooth surfaces.

Imagine pushing a toy car across a hard floor. Now imagine pushing the car on carpet. The car slows down on both floors, then stops. On which floor will the car go farther? Why? The carpet has a rougher surface than a hard floor has. The carpet creates more friction. When there is more friction, an object slows down more quickly.

Surfaces Rubbing Together

What happens when different surfaces rub against each other?
Does the amount of friction change?

What Rubs Together?

How Much Friction?

rough surface rubs on a rough surface

A lot of friction

rough surface rubs on a smooth surface

Medium friction

smooth surface rubs on a smooth surface

Very little friction

To learn more about the force of friction, watch the video by MooMooMath and Science on Youtube.

Now Show What You Know!

Complete some questions about the reading selection by clicking “Begin Questions” below.