# P2.2 The Kinetic eNERGY

- Created by: Anisha
- Created on: 28-04-13 13:08

First 494 words of the document:

P2.2 The kinetic energy of objects speeding up or slowing down

P2.2.1 Forces and Energy

When a force causes an object to move through a distance work is done.

W=F x d

W is the work done in joules: J

F is the force applied in Newton: N

d is the distance moved in the direction of the force in metres: m

Energy is transferred when work is done work done is against frictional forces.

Power is the work done or energy transferred in a given time:

P= E/T

Pthe power in watts: W Ethe energy transferred in joules: J tthe time taken in

seconds: s

Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational

field.

Ep = m x g x h

Ep is the change in gravitational potential energy in joules, J

m is the mass in kilograms, kg

g is the gravitational field strength in Newton per kilogram, N/kg

h is the change in height in metres, m

The kinetic energy of an object depends on its mass and its speed.

Ek = ½ (0.5) x m x v2

Ek is the kinetic energy in joules, J

m is the mass in kilograms, kg

v is the speed in metres per second, m/s

P2.2.2 Momentum

Momentum is a property of moving objects.

P= m x v

p is momentum in kilograms metres per second, kg m/s

m is the mass in kilograms, kg

v is the velocity in metres per second, m/s

In a closed system the total momentum before an event is equal to the total momentum after the event.

This is called conservation of momentum.

P2.3 Currents in electrical circuits

The current in an electric circuit depends on the resistance of the components and the supply.

P2.3.1 Static electricity

When certain insulating materials are rubbed against each other they become electrically charged.

Negatively charged electrons are rubbed off one material and onto the other. The material that gains

electrons becomes negatively charged. The material that loses electrons is left with an equal positive

charge. When two electrically charged objects are brought together they exert a force on each other.

Two objects that carry the same type of charge repel. Two objects that carry different types of charge

attract. Electrical charges can move easily through some substances, for example metals.

P2.3.2 Electrical Circuits

Electric current is a flow of electric charge. The size of the electric current is the rate of flow of electric

charge.

I = Q/t

I is the current in amperes (amps), A

Q is the charge in coulombs, C

t is the time in seconds, s

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