Topic 4 - Energy Flashcards
Equations
Efficiency = useful energy output ÷ total energy output x 100%
Work done = force x distance moved
W = F x d
Gravitational potential energy = mass x gravitational field strength x height
GPE = m x g x h
Power = work done ÷ time taken
P = W ÷ t
OR
Power = energy transferred / time taken
P = E ÷ t
Kinetic energy = 1/2 x mass x speed^2
KE = 1/2 x m x v^2
Energy stores
Chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear
Energy transfers
Mechanically (physical), electrically, by heating, by radiation (light and sound)
What is the energy transfers?
Using the principles of conservation of energy
Work done is the same as…
Work done always equals to energy transfers
Describe power
Power as the rate of transfers of energy or the rate of doing work
Kinetic
Energy contained in moving object, e.g a bullet or a runner
Chemical
Energy stored in fuel (food, batteries etc.) which is released when a chemical reaction takes place, e.g coal, hamburger, cell
Gravitational potential energy
Energy of an object due to its height above a surface , e.g a rollercoaster at the top of the track, a climber
Nuclear
Energy released from nuclear reactions , e.g nuclear power plant, the Sun
Thermal
Energy stored in an object at a certain temperature (due to the random motion of its particles), e.g bonfire, radiator
Magnetic
The energy stored when repelling poles have been pushed closer together e.g magnets held close to each other
Electrostatic
The energy stored when repelling charges have been moved closer together, e.g Van de Graff generator, thunderclouds
Elastic
Energy stored in an object that is being stretched, squashed, e.g stretched bow, catapult
Mechanical work
A force moving an object through a distance, e.g windmill
Electrical work
Charges moving due to a potential difference, e.g light bulb
Heating
Due to temperature difference caused electrically or by chemical reaction,
Radiation
Energy tranferred as a wave, eg light and infrared - light radiation and infrared radiation are emitted from the sun
The principles of conservation energy
- energy can neither be created nor destroyed, it can only be stored or transferred.
- energy being wasted, means it has been transferred in a way that is no longer useful, usually via heating, increasing the thermal energy store of the surroundings.
Sankey diagrams
These diagrams show how much energy is input into different devices and how much energy is transferred into different types of energy. It is possible to use the information in this diagram to work out the efficiency of the device.
What is power?
Power is the rate of doing work – i.e. how much energy is transferred per second.
Unit for power
Watt (One watt = 1 joule of energy transferred per second)
What is work done?
The mechanical work done on an object is the energy transferred to it due to a force acting on the object and causing it to move.
Unit for work done?
J/joules
Describe Gravitational Potential Energy
Gravitational Potential Energy (GPE), depends on its position with respect to the surface of a massive object such as the Earth. The higher you raise an object, the more GPE it stores.
Kinetic Energy depends…
Kinetic Energy (KE), depends on both its mass, AND how fast it is travelling.
GPE to KE transfer (when object is dropped)
- object falls from a height, weight acts on it and hence work is done.
- there is a mechanical transfer, and GPE is transferred to KE in this way.
- This makes sense as we know that a falling object accelerates, so its KE must be increasing.
GPE lost by the falling object = KE gained by it
How does the height dropped from affect the efficiency of the bounce?
As the drop height is increasing, the efficiency reduces at a increasing rate (we will see this better on a graph)
