[Force] [Magnets] [Friction] [Gravity and Upthrust]

Friction is a force that slows things down or tries to stop an object moving

Friction causes grip.

Friction causes heat. The brakes on your bike will bill be hot after they have slowed down the moving wheel.

Without friction your feet would just slip on he ground.

Running shoes need friction to grip the ground

Tyres need friction to grip the road.

       wheels smoking
Wheels spinning on the road makes the tyres get hot and smoke.
Not recommended!
tread
The tread on a car wheel is to help increase the friction between the tyre and the road.
car The man is driving his car towards the right.

The force of friction pushes him to the left

Friction is helpful
Without friction the tyres would just slip on the ground. He would not be able to turn or move.

Friction sometimes does not help
The air pushes against the car when it tries to move. This slows him down

Air resistance is a kind of friction

In the example above the moving air slows the car down.

This kind of friction is called air resistance.

We could make the air resistance less by making the car more pointed (streamlined).
If we did this the car would go faster.

parachute Gravity pulls the parachute down

Air resistance, a kind of friction, pushes the parachute up

 

Bigger parachute = more air resistance = slower falling

 

How can we reduce friction?


By using bearings

By using lubrication (usually oil)

By having a smooth surface such as skis or ice

By using a aerodynamic shape that air slips over easily

Investigating friction (1)

Aim: To find out which surfaces have the most grip (friction)

Diagram

block_sliding
Method (what we did)

We placed weights on a block of wood that had a hook on one end.

We then placed the block of wood on the surface being tested (eg a piece of carpet).

A force meter was attached to the hook and pulled until the block just started to slide.

We measured the force needed to keep the block moving and recorded it in our table of results.

The experiment was repeated several times with different surfaces between the trolley and the bench top.

To keep make it a fair test we kept these factors the same for each experiment:

  • The weight on the block
  • The size of the block
  • The speed of the block after it was moving


Results

Type of surface

Force needed to pull the trolley (N)

Bench top

1N

Carpet

2N

Sand paper

4N

Rollers

0.5N


Conclusion
The wooden rollers had the least friction and the sand paper had the most friction