P1 Conservation and dissipation of energy
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30 Terms
Energy
Something that is needed to make things happen or change; it can be stored in different energy stores
A unit of energy
joule (J)
Chemical energy store
Energy stored in chemical substances
Kinetic energy store
Energy stored in something because it is moving
Gravitational potential energy store
Energy stored in something because of its position above the ground
Elastic potential energy store
Energy stored in stretched or squashed things
Thermal energy store
Energy stored in hot objects
Energy transfers
Energy moves from one store to another, by heating, by waves, by an electric current, or by a force
Law of conservation of energy
Energy cannot be created or destroyed, only transferred from one store to another
A system
An object or group of objects
A closed system
An isolated system in which no energy transfers out of or into the system
Work
The energy transferred by a force when it moves an object
Energy transferred is equal to
Work done
Work done
A measure of the energy transferred when a force acts through a distance
Useful energy
Energy transferred to the store where it is wanted in the way that is wanted
Wasted energy
Energy that is not usefully transferred
Dissipates
Energy spreads out and is stored in less useful ways; eventually it is transferred to the surroundings which become warmer
Efficiency
The proportion of input energy that is transferred to a useful store
Maximum efficiency
1, or 100%
Ways that machines waste energy
Friction between moving parts; air resistance; electrical resistance; noise
Ways to improve machine efficiency
Lubrication of moving parts; low resistance wires
Power
The rate of transfer of energy
The unit of power
watts (W) or kilowatts (kW)
micro (ÎĽ)
One millionth (10^-6)
milli (m)
One thousandth (10^-3)
kilo (k)
One thousand (10^3)
mega (M)
One million (10^6)
giga (G)
One billion (10^9)
The more powerful an appliance is, then
the faster the rate at which it transfers energy
Power wasted by an appliance
Total power input - useful power output