Physics - GPE to KE

There are 8 energy stores:

• kinetic 
• thermal 
• chemical - anything that can release energy by a chemical reaction (e.g. food)
• nuclear
• magnetic
• gravitational potential - anything in a graviational field i.e. can fall
• elastic potential - anything stretched
• electrostatic - two charges that attract or repel each other

There are 4 main energy pathways:

• heating by particles - energy transferred from a hotter object to a colder one
• heating by radiation -energy transferred by waves (e.g. light)
• mechanical working -a force acting on an object and doing work
• electrical working - a charge doing work (e.g. charges moving round a circuit)

E.g. a ball rolling up a hill

the ball does work against gravity

energy is transferred mechanically from its kinetic store to its gravitational potential store

If an object gets faster, energy is transferred to its kinetic store

If an obejct gets slower, energy is transferred away from its kinetic store

the amount of energy in its kinetic store depends on its speed and mass

KE = 1/2 x m x v2

KE = 1/2 x mass x speed2

m = kg, v = m/s2

mx2 = KEx2

vx2 = KEx4 ( because it's squared)

An object at any height above the Earth's surface will have energy in its gravitational potential store

change in GPE = m x g x change in h

change in GPE = mass x gravitational field strength x change in height

m = kg, g = N/kg, h = m

Gravitational field strength on Earth = 10N/kg

There is no net change to the total energy in a closed system

i.e. if energy increases/decreases, its not a closed system

you can make a system closed by increasing the number of things you treat as part of it 

e.g.heating water on a hob = loss of thermal energy to surroundings

but: pan + gas + surroundings = closed system

when work is done mechanically, frictional forces must be overcome (e.g. air resistance, friction) and the energy used to do this is transferred to thermal energy stores of the object and its surroundings

dissipated = energy is spread out to non-useful stores, i.e. lost

E = F x d

Work done = force x distance

E = J, F = N, d = m

When a force moves an object through a distance, work is done and energy is transferred

change in GPE or KE is equal to work