4.1.1.2 Changes in energy

Kinetic energy

Any moving object

Energy is transferred to this store when an object speeds up

Energy is transferred away from this store when an object slows down

What does energy in kinetic energy store depend on

The objects mass and speed

The greater it’s mass and the faster it’s going, the more energy there will be in KE store

Kinetic energy equation

Ek = 1/2 mv²

Kinetic energy = 0.5 x mass x (speed)²

Energy, Ek, J

Mass,m, kg

Speed, v, m/s

Elastic potential energy

Stretching or squashing an object can transfer energy to its elastic potential energy store

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What is limit of proportionality

When extension is no longer directly proportional to the force applied

It will not return back to original length if force is taken away

Elastic potential energy equation

elastic potential energy = 0.5 × spring constant × extension^2

Ee = 1/2 Ke^2

Elastic potential energy, Ee, J

Spring constant, k, N/m

Extension ,e,

Gravitational potential energy

Energy store of raised objects

Dependent on objects mass, height, gravitational field strength

The higher object = higher gpe

Gravitational potential energy equation

g. p . e . = mass × gravitational f ield strength × height Ep =mgh

gravitational potential energy, Ep, in joules, J

mass, m, in kilograms, kg

gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation the value of the gravitational field strength (g) will be given). height, h, in metres, m

Energy in falling objects

When something falls, energy from its gravitational potential energy store is transferred to kinetic energy store

For a falling object when there’s no air resistance:

Energy lost from gpe store = energy gained in kinetic energy store

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Air resistance causes some energy to be dissipated to thermal energy store of surroundings