Albert Teen

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Contact Forces

# Contact Forces

### Contact Forces

Here you will cover one of two types of forces, contact.

1

Which of these objects would you say are "in contact" with each other?

A) The man and the car B) The ball and the ground

2

These are two different forces

The man exerts a pushing force on the car. The Earth exerts the force of gravity on the ball.

3

Which one of these two forces do you think is a contact force and not a non-contact force?

A) Pushing force B) Gravity

4

Forces can be divided into two categories

Contact forces require two objects to be in direct contact with each other. Non-contact forces do not.

1

When you slam your brakes on your bike to slow down, that exerts a ___________ force between the brake-pads and the tyre.

A) contact B) non-contact

2

What kind of contact force is it though?

A) Pushing force B) Pulling force C) Friction

3

So friction is a type of contact force

For example, friction between the brake-pads and the tyre will eventually make the tyre run out of energy, and the bike will come to a stop.

4

If you were to touch the brake-pads on your bike right after you'd slammed them on, you'd realise that they had gotten ________.

A) soft B) warm C) cold

5

So friction is a contact force that impedes motion

It always acts in the opposite direction to a moving object, and it results in heating.

Reducing friction

1

Now when it comes to your bike chain, you want as little friction as possible! What do you do to reduce friction in the chain?

2

Friction can be reduced by lubricating the surfaces

For example when you oil the chain on a bike to make it run more smoothly, or when you oil a door handle to make it stop squeaking.

1

This is an example of tension. Tension is a kind of __________ force.

A) pulling B) pushing

2

Tension is also a contact force

It is a pulling force that is exerted by a stretched object, like a rope or a cable.

1

When an object is falling through the air...

it experiences both the force of gravity and air resistance.

2

Air resistance is a type of contact force. Which type?

A) Tension B) Friction C) Pushing

3

So air resistance is a frictional force. It occurs when the object collides with...

A) air particles in the air. B) particularly strong winds. C) insects in the air.

4

Air resistance is a frictional force between the object and the particles in the air

It acts on all objects that move around in air, whether along the ground (like a car) or falling through the air (like this skydiver).

1

This is an example of a "normal contact force". It's acting at a _________ angle.

A) $45^{\circ}$ B) $90^{\circ}$ C) $0^{\circ}$

2

Normal contact forces always act at right angles

For example a book resting on a table.

1

Summary! Contact forces require two objects to be in direct contact with each other

Non-contact forces do not.

2

Friction is a contact force

Friction always acts in the opposite direction of a moving object, and it results in heating.

3

Tension is also a contact force

It is a pulling force that is exerted by a stretched object, like a rope or a cable.

4

Normal contact force

This is what we call it when a contact force is acting at a $90^{\circ}$ angle, like a book resting on a table.