YOU ARE LEARNING:
Contact Forces
Contact Forces
Here you will cover one of two types of forces, contact.
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
These are two different forces
The man exerts a pushing force on the car. The Earth exerts the force of gravity on the ball.
Which one of these two forces do you think is a contact force and not a non-contact force?
A) Pushing force B) Gravity
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.
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
What kind of contact force is it though?
A) Pushing force B) Pulling force C) Friction
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.
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
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
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?
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.
This is an example of tension. Tension is a kind of __________ force.
A) pulling B) pushing
Tension is also a contact force
It is a pulling force that is exerted by a stretched object, like a rope or a cable.
When an object is falling through the air...
it experiences both the force of gravity and air resistance.
Air resistance is a type of contact force. Which type?
A) Tension B) Friction C) Pushing
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.
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).
This is an example of a "normal contact force". It's acting at a _________ angle.
A) B) C)
Normal contact forces always act at right angles
For example a book resting on a table.
Summary! Contact forces require two objects to be in direct contact with each other
Non-contact forces do not.
Friction is a contact force
Friction always acts in the opposite direction of a moving object, and it results in heating.
Tension is also a contact force
It is a pulling force that is exerted by a stretched object, like a rope or a cable.
Normal contact force
This is what we call it when a contact force is acting at a angle, like a book resting on a table.