# Physics - P1.2 - Using Energy

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## P1.2.1 - Forms of Energy

• Types of energy - light, sound, kinetic, nuclear, electrical, gravitational potential, elastic potential, chemical - last three = forms of stored energy
• Energy can be transferred from one form to another
• Any object above the ground has gravitational potential energy
• Falling object transfers gravitational potential energy -> kinetic energy
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## P1.2.2 - Conservation of Energy

• Not possible to create or destroy - possible to transfer it from one form or place to another
• Conservation of energy - total amount of energy is always the same, applies to all energy transfers
• Falling object - gravitational potential energy -> kinetic energy
• Stretching an elastic band - chemical energy -> elastic potential energy
• Solar cell - light energy -> electrical energy
• Swinging pendulum - gravitational potential energy -> kinetic energy and back as it swings
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## P1.2.3 - Useful Energy

• Machine - something that transfers energy from one form or place to another
• Energy we get out of a machine consists of: useful energy - transferred to place and form wanted, wasted energy - not usefully transferred
• Useful and wasted energy eventually transferred to surroundings and make them warm up
• Energy spreads out - becomes more difficult to use for further transfers
• Energy often wasted because of friction between moving parts of machine - warms machine and surroundings
• Friction may be useful - brakes of bike or car
• Some kinetic energy of vehicle transferred to energy heating brakes
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## P1.2.4 - Energy and Efficiency

• Joules (J) - unit for all forms of energy
• Input energy - energy supplied to machine
• Input energy = useful energy transferred + energy wasted
• Less wasted energy = more efficient
• Efficiency = useful energy transferred by appliance
total energy supplied to appliance      X 100
• Left as a fraction or multiplied by 100 to give %
• No appliance = 100% efficient - except electrical heater - usefully transfers all electrical energy supplied to heating surroundings
• Energy transferred through appliance represented with sankey diagram
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