Please enable JavaScript.
Coggle requires JavaScript to display documents.
P1 pages 170 - 171 (power - the rate of energy transfer, or the rate of…
P1 pages 170 - 171
power - the rate of energy transfer, or the rate of doing work
-
-
-
a powerful machine is not nessecerily one which can exert a strong force, although it usually works out this way. a powerful machine is one which transfers a lot of energy in a short space of time
-
-
-
-
when energy is transferred between stores, not all of the energy is transferred usefully into the store that you want it to go. some energy is always dissipated when an energy transfer takes place. dissipated energy is sometimes called wasted energy because the energy is being stored in a way that is not useful (usually energy has been transferred into thermal energy stores)
for example 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 this energy is dissipated in this transfer to the thermal energy store of the phone and that is why it feels warm after using it for a long time.
an example of an energy transfer in a closed system is when a cold spoon is dropped into an insulated flask of hot soup, which is then sealed. you can assume that the flask is the perfect thermal insulator so the spoon and soup form a close system. energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon (causing the soup to cool down slightly). energy transfers have occurred within the system, but no energy has left the system, so the net change in energy is zero.