4.2.1 - 4.2.7 - Work, Power and energy transfer Flashcards
What is work?
Work is done when an object is moved over a distance by a force applied in the direction of its displacement
It is said that the force does work on the object
If a force is applied to an object but doesn’t result in any movement, no work is done
What occours when work is done?
When work is done on an object, energy is transferred
The amount of energy transferred (in joules) is equal to the work done (also in joules)
energy transferred (J) = work done (J)
How does energy change if a force acts in the direction that an object is moving?
If a force acts in the direction that an object is moving, then the object will gain energy (usually to its kinetic energy store)
How does energy change if a force acts in the opposite direction that an object is moving?
If the force acts in the opposite direction to the movement then the object will lose energy (dissipated to the surroundings usually by heating)
What is work being done and give an example?
Work is done on a ball when it is lifted to a height
The energy is transferred mechanically from the ball’s kinetic energy store to its gravitational potential energy store
Work is done when a bird flies through the air
The bird must travel against air resistance, therefore energy is transferred from the bird’s kinetic store to its thermal store and dissipated to the thermal store of the surroundings
What is the eq. for work done?
Work done = Force x Distance
What is gravitational potential store?
The energy an object has due to its height in a gravitational field
How does energy change within the gravitational potential store?
If an object is lifted up, energy will be transferred to its gravitational store
If an object falls, energy will be transferred away from its gravitational store
What is the eq. for gravitational potential energy?
Gravitational potential energy = Mass x gravitational field strength x height
How does Gravitational field strength change between planets and moons
The gravitational field strength (g) on the Earth is approximately 10 N/kg
The gravitational field strength on the surface of the Moon is less than on the Earth
This means it would be easier to lift a mass on the Moon than on the Earth
The gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) is more than on the Earth
This means it would be harder to lift a mass on the gas giants than on the Earth
What is kinetic energy?
The amount of energy an object has as a result of its mass and speed
This means that any object in motion has energy in its kinetic energy store
What is the eq. for calculating the amount of Kinetic energy?
Kinetic energy = 1/2 x mass x velocity 2
How is energy transferred with mechanical work?
Whenever mechanical work is done (when a force acts over a distance), energy is transferred mechanically . The amount of energy transferred (in joules) is equal to the work done (in joules or newton-metres)
What is perfect energy transfer?
In a perfect energy transfer, there is no wasted energy
Energy transfers can be assumed to be perfect if the wasted energy transfer is negligible
What is an example of perfect energy transfer
Pendulums are often used as examples of perfect energy transfers
All of the energy in the kinetic store of the pendulum is transferred mechanically into its gravitational potential store
And then all of the energy in the gravitational potential store of the pendulum is transferred mechanically into its kinetic store
Energy is transferred back and forth between these two stores as the pendulum swings
KE total = GPE total
What is power?
The rate of this energy transfer, or the rate of work done, is called power
Why is time important with power?
Time is an important consideration when it comes to power
Two cars transfer the same amount of energy, or do the same amount of work to accelerate over a distance
If one car has more power, it will transfer that energy, or do that work, in a shorter amount of time
What is the calculation for power?
Power = Work / Time
What are energy resources?
Energy resources are large stores of energy that can be used to generate electricity and heat homes and businesses
What is renewable energy source?
An energy source that is replenished at a faster rate than the rate at which it is being used
What are some examples of renewable energy sources?
Renewable resources include:
Solar energy
Wind
Bio-fuel
Hydroelectricity
Geothermal
Tidal
What are some examples of non renewable?
Fossil Fuels (coal, oil and natural gas)
Nuclear fuel
How is electricity produced in a turbine?
A turbine is turned, which turns a generator, which generates electricity
The element that differs is how the turbine is made to turn
Water can be used to turn turbines in the case of hydroelectric dams, tidal barrages and tidal turbines
Energy in the kinetic store of the flowing water is transferred to the kinetic store of the turbine and then to the kinetic store of the generator and transferred electrically to the National Grid
Fossil fuels can be combusted to heat water, and the steam produced can be used to turn turbines
Energy from the chemical store of the fuel is transferred to the thermal store of the water, which is then transferred to the kinetic store of the turbine, and then transferred to the kinetic store of the generator and then transferred electrically to the National Grid
How can nuclear fuel be used to turn turbines?
Nuclear fuel can also be used to heat water to produce steam to turn turbines
The energy transfers involved in electricity generation from a nuclear power plant are:
Nuclear store of fuel → thermal store of water → kinetic store of turbine → kinetic store of generator
Geothermal energy is another way to produce the steam that turns the turbines
Water is pumped down to the hot rocks and returns through a fissure as steam
What are all of the energy resources?
What is a reliable energy source?
A reliable energy resource is one that can produce energy at any time
What is a non reliable energy source?
Non-reliable resources can only produce energy some of the time (e.g. when it’s windy)
Compare the energy resources?
What are some more energy sources and how do they compare?
