Theory

Def: A force is anything, which changes or tries to change the motion of a body

 

Force is measured in Newtons (N).

 

Def: The weight of a body is the force pulling it towards the centre of the earth.

 

Weight is measured in Newtons (N)

 

Weight (in Newtons) = mass (in kgs) x10

 

Work = Force x Distance, the unit of work is the joule (j) which is also the unit of energy.

 

Def: Power is the amount of work done per second.

 

Power is measured in watts (w)

 

1 watt means 1 joule per second.

 

1,000 watts = 1 Kilowatt

 

Newtons Third Law: To every action there is an equal and opposite reaction.

 

E.g. Fire a bullet from a gun.

Action: Bullet goes forward.

Reaction: Gun goes back (recoils)

 

Def: Friction is a force that tries to stop things sliding over each other.

 

Def: Lubricants are substances that reduce friction.

 

·        Uses of Friction: Give shoes grip on the ground, brakes to stop cars and bicycles.

 

·        Disadvantages of Friction: Joints of machinery get worn down and the joints have to be oiled to reduce friction.

 

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