P1 - conservation of energy and Power

conservation of energy principle
1. the conservation of energy principle is that energy is always conserved
  1. energy can be transferred usefully, stored or dissipated but can never be created or destroyed.
2. when energy is transferred between stores, not all of the energy is transferred usefully into the store that you want it to go to. Some energy is always dissipated when an energy transfer takes place.
3. dissipated energy is sometimes called 'wasted energy' because the energy is being stored in a way that's not useful.
4. A mobile phone is a system. when you use the phone, energy is usefully transferred from the chemical energy store of the battery in the phone. but some of the this energy is dissipated to the thermal store of the phone
5. energy transfers for closed systems
  1. a cold spoon is dropped into an insulated flask of hot soup, which is then sealed
    1. you can assume that the flask is a perfect thermal insulator so the spoon and the soup form a closed system.
      1. energy is transferred from the thermal energy store o f the soup to the useless thermal store of the spoon (causing the soup to cool down slightly). Energy transfers have occurred within the system, but no energy has left - so the net change in energy is zero
power is the 'rate of doing work'
1. power is the rate of energy transfer or the rate of doing work
2. Power is measured in watts. One watt = one joule of energy transferred per second
3. EQUATION - P = E/t
  1. Power(W) = energy transferred(J) / Time(s)
4. EQUATION = P = W/t
  1. Power(W) = Work done(J) / Time(s)
5. A powerful machine isn't necessarily one which can exert a strong force (although it usually ends that way). A powerful machine is one which transfers a lot of energy in a short space of time

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P1 - conservation of energy and Power

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	Created by Flo Sumpter over 3 years ago