Topic 8 - Forces Doing Work Flashcards
Describe the changes involved in the way energy is stored when systems change
Energy can be transferred between stores mechanically, electrically, heating or by radiation
What happens when there are energy transfers in a closed system?
There is no net change to the total energy in that system
How can energy of a system change in heating?
Eg when pan of water is heated energy is transferred into the system by heating to thermal energy stores of pan + water which increases temperature.
How can energy of a system change through work done by forces?
Eg box is the system. As box is lifted work is done against gravity. Causes energy transferred to box’s kinetic + GPE stores.
How can energy of a system change in electrical equipment?
Eg hair dryer is a system. Transfers energy into system electrically from mains supply to kinetic energy store of fan inside it. Transfers energy electricity to thermal energy store of heating element + sound
What happens when a force moves an object through a distance?
Work is done on the object and energy is transferred. (Energy transferred J = work done J)
What is the equation for work done?
Work done (J) = Force (N) x distance (m) E = F x D
What is the equation for gravitational potential energy?
Change in GPE (J)= Mass (kg) x gravitational field strength (N/kg) x change in vertical height (m)
GPE = m x g x h
What is the equation for kinetic energy?
KE (J) = 0.5 x mass (kg) x (speed)2 m/s
KE = 0.5 x m x v2
What happens when a system changes?
Energy is transferred and some energy is dissipated + stored in less useful ways
What is power?
The rate at which energy is transferred. Eg if electric heater had power of 600W it transfers 600J of energy every second.
What is the equation for power?
Power (W) = work done (J) / time taken (s)
P = E / t
What is one watt equal to?
One watt = one joule / second
What is a force?
A force is a push or pull on an object caused by it interacting with something
