Topic 8 Energy- Forces Doing Work(complete) Flashcards
When a system changes energy is transferred
In a closed system there are no net changes to the total energy
What are the 3 ways energy of a system can be changed
Heating
Forces doing work
Electrical equipment
Give example of how energy of a system change in heating
In pan of water energy transferred into system by heating to the thermal store of pan and water
How does energy of a system change in forces doing work
When you lift a box off the ground
Energy stores transferred to boxes gravitational potential energy and kinetic energy store
How does energy of a system change in electrical equipment
Electric irons transfer energy electrically from the mains electricity to the thermal energy store
What is the formula for work done
Work done= Force >< Distance
When you are doing work you are applying a force on something to move it which creates some sort of friction which causes energy transfer to thermal store and wasted
In all system changes energy is dissipated so it is stored in less useful ways
What is power
How much work is done per second
Watts
What is the formula for power
Power= work done(J)/time taken(s)
1 Watts=1 J/s
What is the formula for gravitational potential energy
GPE=m><g><h
Mass
Gravitational field strength
Change in height</g>
What is the formula for kinetic energy
KE=1/2><m><v^2
Mass
Velocity</m>
What is the formula for efficiency
Efficiency =useful energy transferred by the device/total energy supplied to device
