Albert Teen
Forces in Motion

YOU ARE LEARNING:

Inertia

# Inertia

### Inertia

You will learn to grasp what is meant by inertia, which applies to all objects at rest or in uniform motion.

Imagine a book sliding across a school bench. It will eventually stop moving and remain at rest. Why is this?

If there were no frictional force between the surfaces of the book and the table, how would the motion of the book change?

True or false? An unbalanced force is needed to keep an object in motion.

All objects have a natural tendency to carry on in the same state of motion. This is why objects at rest will remain at rest, and objects in motion will remain in motion in the absence of an unbalanced force. We call this inertia. It is resistance to a change in motion.

1

In the first image, a driver is travelling north along a road at $40\space mph$ . If all of the forces acting on the car are balanced, it will...

A) speed up in the direction of motion. B) slow down because there is no force to keep it moving. C) continue at the same speed and in the same direction.

2

If the car is moving at $40\space mph$, is the driver also moving at this speed? Answer yes or no.

3

The driver spots a cat on the road and applies the brakes to stop suddenly. The brakes provide an unbalanced force to slow the car down. Why does the driver get thrown forwards?

A) He continues to move at 40 mph. B) A force pushes him forwards. C) He has an unbalanced force acting upon him.

4

When the car brakes suddenly, an unbalanced force acts on the car but not on the driver, so he continues to move at the same speed and in the same direction. This is because of inertia.

Luckily the driver is wearing his seat belt. The seat belt provides a force to change the motion of the driver, and stop him from hitting the windscreen at $40\space mph$!

All objects have inertia, but some more than others. Which do you think has greater inertia?

If a car has more inertia than a bicycle, and a truck has more inertia than a car, what do you think the relationship is between inertia and mass?

The more massive an object, the greater its tendency to resist changes to its state of motion. This is why you couldn't push a truck to get it moving, but you could push a bicycle.

An elephant has more inertia than a human. What does this statement tell us about the elephant? Pick all the options you think are correct.