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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…

Page 2

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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…

Page 3

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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…

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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…

Page 5

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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.…

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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…

Page 7

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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…

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