# Lesson 04 – The Force of Friction

## Vocabulary

Force

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

Friction

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

Movement

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?