Physics Summary Notes - Mechanics and Heat - Friction

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Unit 1.2 - Friction
Friction is a force which usually opposes the motion of the object.
Sometimes a lot of friction is wanted. Friction can be increased in the following ways:
Using a suitable choice of substances (e.g. rubber tyres on a tarmac road)
Applying the brakes in a car
Increasing the force holding the two forces together (e.g. aerofoils on racing cars or pulling
bike brakes harder)
Usually, we want to make the force of friction as small as possible. Friction can be reduced in the
following ways:
Using a suitable choice of substances (e.g. ice and ice skates)
Using lubrication (e.g. oil in the moving parts of machinery & wax on skis)
Preventing two surfaces from coming into contact (e.g. wheels)
Friction wastes energy by converting it into heat.
EXPERIMENT ­ MEASURING FRICTION
Aim- to see whether or not different types of material affect the amount of friction between moving
surfaces.

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Method:
Pull the wooden blocks with the different materials on the friction board at a steady speed using the
newton balance.
Type of Material Force of friction (N)
Polystyrene 3.46
Medium sandpaper 4.92
Metal 3.14
Vinyl 2.5
Plastic 2.28
Rubber 3.22
Paper 2.96
Emery cloth 4.12
Wood 3.5
Wool 3.38
Cardboard -
Felt 4.2
Rankings
I. Medium sandpaper
II. Felt
III. Emery cloth
IV. Wood
V.…read more

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VI. Wool
VII. Rubber
VIII. Metal
IX. Paper
X. Vinyl
XI. Plastic
Balanced & Unbalanced Forces
Usually, in real situations, more than one force acts on an object at the same time.
There are two possible outcomes.
Balanced and Unbalanced forces
Balanced forces:
This is where the opposite forces act on one objects and cancel each other out.…read more

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Newton's First Law
This law tells us what happens to an object when an unbalanced force acts upon it.
The law is:
A linear air track can be used to show this law working. Normally, this is difficult because the force of
friction slows things down if they are pushed and then left alone.…read more

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Car seatbelts are necessary to stop people being badly injured in a crash. Without the seatbelt,
Newton's First Law tells us that the person will keep moving forward when the car stop until they hit
something that slows them down. This is because they are not attached to the car.
This is also why people appear to be "thrown forward" when a bus stops if they are standing on the
isle.
A seatbelt applies an unbalanced force which stops in a safer, more controlled way.…read more

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M = Mass in kilograms (Kg)
A = acceleration in ms-2
Definition of a Newton
The definition of the unit of force is linked to Newton's Second Law:
ONE newton is the force required to accelerate ONE kilogram at a rate of ONE ms-1
Acceleration due to gravity
Falling objects accelerate because of gravity. The acceleration due to gravity is always 10ms-2
(roughly) for any freely falling object on earth.…read more

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Horizontally, the speed of the projectile is constant. So we use the equation:
Vertically, the projectile is changing velocity. It is accelerating downwards because of gravity. So we
use the equation:
The important point is that the horizontal and vertical movements do not affect each other. Only the
time of flight can be used in calculating both the horizontal and vertical motions.…read more

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