Energy Transfers Flashcards
What is the unit of mass?
Kilogram (kg)
What is the unit of speed?
metres per second (m/s)
What is the unit of energy?
Joule (J)
What is the unit of power?
Watt (W)
What is the unit of efficiency?
DOESN’T HAVE ONE, TRICK QUESTION, HAHAHAHAOr percent, kinda, but its not a real unit
What is power?
Energy transferred by a system per second
What is efficiency?
The fraction of total energy converted into useful energy.
What is the equation for GPE?
GPE = mgh
What is the equation for KE?
KE = 1/2 m v^2 (half m v squared)
What is the equation for efficiency, in terms of energy?
Efficiency = Useful Energy / Total Energy
What is the equation for efficiency, in terms of power?
Efficiency = Useful Power / Total Power
What is conduction?
Heat transfer due to collisions between particles.
Give an example of conduction.
Heat transferring through a piece of metal, like a frying pan on a stove.
What is convection?
Heat transfer due to the movement of fluids of differing densities.
Give an example of convection.
The movement of air in a room due to a heater.The movement of water around a cooking pot.
Explain convection.
The fluid heats up.The particles spread out.The fluid becomes less dense.The fluid rises due to buoyancy.The fluid is replaced by colder fluid.The process repeats.
Why does a blanket keep somebody warm?
Heat loss due to CONVECTION is reduced by the air being trapped.
Heat loss due to CONDUCTION is reduced by the trapped air and the blanket being poor conductors.
Heat loss due to EVAPORATION is reduced because you sweat less under the blanket (as there is little air flow and the air is saturated).
How do you increase heat loss due to conduction?
Make the object out of a metal ( a good conductor)
Increase the contact surface area.
How do you increase heat loss due to convection?
Remove the lid/open it up
Remove anything that inhibits airflow, like cotton wool
How do you increase heat loss due to radiation?
Increase the surface area (by adding fins)
Paint the object matte black.
What are the properties of white, shiny surfaces?
They are good REFLECTORS of radiation.
They are poor EMITTERS and ABSORBERS of radiation.
What are the properties of black, matte surfaces?
They are poor REFLECTORS of radiation.
They are good EMITTERS and ABSORBERS of radiation.
What is the equation for power?
Power = Work Done / Time
What is the cheat equation for the speed of an object as it hits the floor when dropped from a certain height?
v = Square root of ( 2 g h )
