Chapter 5: Work, Energy And Power Flashcards
(26 cards)
Work done definition
In physics work done is when an object is displaced by an external force allljed in the direction of its displacement.
Work done formula
W = Fs
1Nm = 1 J
State the principle of conservation of energy.
Energy cannot be created or destroyed, it can only be transferred from one energy store to another. This means that the total amount of energy in a closed system remains constant.
Explain the energy transfers in:
A falling object (in a vacuum)
E.g.: A ball rolling down the hill.
Gravitational potential to kinetic
Explain the energy transfers in:
Horizontal mass on a spring
Elastic potential to kinetic
Describe the energy store: kinetic
Moving objects have energy in their kinetic store
Describe the energy store: gravitational potential
Objects gain energy in their gravitational potential store when they are raised through a gravitational field.
Gravitational potential energy is the energy stored in a mass due to its position in a uniform gravitational field.
Describe the energy store: elastic
Objects have energy in their elastic potential store if they are stretched or compressed.
Describe the energy store: electrostatic
Objects with charge interacting with one another have energy in their electrostatic store.
Describe the energy store: magnetic
Magnets interacting with each other have energy in their magnetic store.
Describe the energy store: chemical
Objects with energy in their chemical store can release energy in chemical reactions.
Describe the energy store: nuclear
Atomic nuclei release energy from their nuclear store during nuclear reactions.
Describe the energy store: thermal
All objects have energy in their thermal store; the hotter an object is, the more energy it has in this store.
Describe the energy transfer: mechanical
When a force acts on an object e.g: pulling, pushing, stretching, squashing etc..
Describe the energy transfer: electrical
A charge moving through a potential difference e.g. electrons flowing around a circuit.
Describe the energy transfer: by heating
Energy is transferred from a hotter object to a colder one.
Describe the energy transfer: by radiation
Energy is transferred by electromagnetic radiation
What is the energy transfer in a television?
Energy is transferred from electrical energy to thermal energy, light energy and sound energy.
But the energy is dissipated (wasted) by heating to the thermal energy store of the surrounding air.
Explain the energy transfers in a heater.
Energy is transferred from electrical store to thermal store
Efficiency of a system definition
The efficiency of a system is the ratio of the useful energy output from the system to the total energy input.
Definition of power (2 ways)
The rate if energy transfer.
Work done per unit time.
Efficiency formula (in 2 ways)
Efficiency = (useful energy output)/(total energy input)*100%
Efficiency = useful power output/total power input
Power formula (number 1)
P = E/t = W/t
Power formula (n.o. 2) for a moving object and its derivation
P = Fv
Only relevant if a constant force moves a body at a constant velocity
P = W/t = Fs/t = Fvt/t = Fv
