Energy - forces doing work Flashcards
what is a system?
a single object or a group of objects that you are interested in
what happens when a system changes?
energy is transferred.
in what way is energy transferred?
it can be transferred into or away from the system, between different objects in the system or between different types of energy stores
what always happens when energy is transferred?
some energy is dissipated and stored in less useful ways
what is a closed system?
a system that is defined so that net change in energy is zero
three ways energy can be transferred?
by heating, by forces doing work, by electrical equipment
Energy being transferred by heating - a pan of water heated on a gas stove - the system being the pan of water
energy is transferred into the system by heating to the thermal energy stores of the pan and water which increases their temp
Energy being transferred by heating - a pan of water heated on a gas stove - the system being the camping stove and the pan
energy is transferred from the chemical energy store of the gas to the thermal energy stores of the pan and the water, increasing their temp
energy transferred by forces doing work - a box is lifted and the box is the system
as the box is lifted, work is done against gravity
this causes energy to be transferred to the box’s kinetic and GPE store
energy being transferred by electrical equipment
how do they work?
example of electrical irons
they transfer energy between different energy stores
electric irons transfer energy electrically from the mains power supply to the thermal store of their metal plates
Describe how to measure work done by a force
when a force moves an object through a distance, work is done on the object and energy is transferred
work done equation
work done = force x distance moved in direction of force
what is the GPE equation?
GPE = m x g x h
what is the kinetic energy equation?
KE = 1/2 x mass x speed (squared)
what else e does a force cause?
what does this mean for the efficiency?
a rise in temperature as energy is dissipated into the thermal energy stores of the moving object and its surroundings - the process is wasteful and the efficiency of the process is reduced
