# Friction

Newtons 1st law says that a body should stay moving at the same speed unless acted on by another force.

What about when we kick a ball down the road, does it keep rolling forever ?? No!?!?

If the car you were in ran out of petrol would it keep going at the same speed? No!?!?

What stops them?

according to Newton,

there must be a force acting on the body

OK!! So! What force stops it.

friction,

Friction is a force between 2 bodies in contact. The Force opposes motion

Friction is a measure of the force of resistance exerted by two surfaces in contact.

mu is a value that depends on the surfaces in contact.

The biggest value mu can have is one and a surface pair that had no friction mu would = 0.

R is the resultant, this comes from Newtons third law.

In all of the cases we will deal with Resultant = Weight of Body

R = W*

OP5 Investigate friction

How could you measure friction?

N = Newtons g = grams

1. Use the spring Balance to find the mass of the block (g)
2. Use the spring Balance to find the Weight of the block (N)
3. Identify 5 surfaces you could measure the friction of (tinfoil, sandpaper, clingfilm, desk, water?)
4. Set up the block and pull it with the Newton Balance
5. Read the value on the balance in NewtonsPut all the values in the Table
6. repeat 3 times for each surface.

Results

Mass of Block = ______ g

Weight of Block = ______ N

Conclusions

The friction between the block & _______ is greatest

The friction between the block & _______ is least

The size of the Friction force is caused by the microscopic arrangement of the material.

extensions

name a material that you think would have a higher reading for friction

change the mass of the block and determine the relationship and a value of the frictional coefficient

change the surface area and show any relationship here.

using the same type of material use a block that has a different mass,

Sometimes Friction causes us to do more work !

We can decrease friction by lubrication.

Carry out the friction test again on one surface,

wet it with water, and carry it out again,

note your results in a table similar to this

what would you say about the coefficent of friction between the following surfaces

shoe vs ice

Imagine if there were no forces between 2 surfaces, if one surface slid over the other effortlessly

Why is it easier to walk on a path than it is on an ice rink?

cycling ?

brakes ?

can you give another 3 everyday applications of friction

Are there any effects on friction that hinder us ?

Braking distance

http://www.fearofphysics.com/Friction/friction.html

Why do drivers need to take into account the weather on the roads?

heres some unexpected friction!

A Jar of rice and pencil

Take a Pencil and stick it in a jar of rice,

What do you think will happen when I pull out the pencil?