Heating, waves or by a force when it moves an object
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Closed system
A system in which no energy transferes take place out of or into the enery stores of the system
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Conservation of energy
Energy can't be created or destroyed.
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Work done equation
force (N) x distance moved along line of force (m) = work done (J)
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Gravitational potential energy increases when...
...it moves up and decreases when it moves down
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Change in GPE equation - using weight
weight (N) x change in height (m) = change in GPE (J)
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Chnage in GPE equation - using mass
mass (kg) x gravitational field strength (N/kg) x change in height (m) = change in GPE (J)
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Kinetic energy equation
Kinetic energy (J) = 1/2 x mass (kg) x speed2^ (m/s)
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Elastic potential energy equation
Elastic potential energy (J) = 1/2 x spring constant (N/m) x extension2^ (m)
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What happens to waste energy in any system?
It is dissipated (spreads out) and may be stored in less useful ways.
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Efficiency of a device
useful output energy / total output energy (J)
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How do machines waste energy?
Friction between moving parts causes heating, resistance of wire causes it to get hot when current passes through it, air resistance and sound
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Improving efficiency of devices
Lubricate moving parts to reduce friction, (in circuits) use wires with little electrical resistance, streamline shapes of moving objects to reduce air resistance, cut out noise (e.g. tighten object to reduce vibration)
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Light bulb - useful energy and waste energy
Useful - light, waste - heat from filament
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Electric heater - useful energy and waste energy
Useful - thermal energy, waste - light emitted from glowing element
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Electric toaster - useful energy and waste energy
Useful - energy heating bread, waste - energy heating toaster case
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