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Work (in terms of energy)
A measure of the energy transferred from one store to another
Work (in terms of forces)
When the force causes a displacement of the object
W = Fd
The equation linking work, force and distance (moved in the direction of the force)
Unit for energy and work
Joules (J)
Unit for force
Newtons (N)
Unit for distance
Metres (m)
What one joule is equal to
The amount of work done done when a force of one newton causes a displacement of one metre (1 J = 1 Nm)
Alternative unit for work done by a force
Newton-metre (Nm)
Effect of doing work against friction
Work done against the frictional forces acting on an object causes a rise in the temperature of the object
Power
The rate at which energy is transferred or work is done
P = E/t
The equation linking power, energy transferred and time
Unit for power
Watts (W)
Unit for time
Seconds (s)
One watt is equal to
An energy transfer of one joule per second (1 W = 1 J/s)
P = W/t
The equation linking power, work done and time
Kinetic energy
The energy of a moving object
Ek = 1/2 mv²
The equation linking kinetic energy, mass and speed
Unit for mass
Kilograms (kg)
Unit for speed or velocity
Metres per second (m/s)
Gravitational potential energy
The energy of an object raised against gravity
Ep = mgh
The equation linking gravitational potential energy, mass, gravitational field strength and height
Unit for gravitational field strength
Newtons per kilogram (N/kg)
Unit for height
Metres (m)
Efficiency
A measure of how good a device is at transferring energy input to useful energy output
Total input energy
The total amount of energy supplied to a device
Useful energy output
The amount of energy that is transferred to useful energy stores
Wasted energy output
The amount of energy that is wasted or dissipated to the surroundings
Efficient device
A device that wastes very little of its input energy
Inefficient device
A device that wastes most of its input energy
Efficiency = useful output energy transfer ÷ total input energy transfer
The equation linking efficiency, useful output energy transfer and total input energy transfer
Efficiency = useful power output ÷ total power input
The equation linking efficiency, useful power output and total power input
Percentage efficiency
Found by multiplying the efficiency by 100
What is meant by an efficiency greater than 1 or 100%
More energy is being transferred than is being supplied
Why can't you have an efficiency greater than 1 or 100%
This would would break the law of conservation of energy as it would mean that energy is being created
Reasons devices waste energy
Friction between their moving parts
Heat due to electrical resistance
Unwanted sound or light
(higher-tier only)
How to improve efficiency
Reduce the amount of energy that a device wastes or dissipates to the surroundings
(higher-tier only)
Ways to improve efficiency
Lubricate mechanical devices to reduce the friction between moving parts of the machine
Insulate heating devices to reduce the dissipation of thermal energy to the surroundings
Energy resource
A useful supply or store of energy
Non-renewable
Energy sources that they are being used at a higher rate than they can be replaced so will eventually run out (finite)
Examples of non-renewable resources
Fossil fuels (coal, crude oil, natural gas), nuclear fuels (uranium, plutonium)
Finite
Something that has a limited number of uses before it runs out
Renewable
Energy sources that are (or can be) replenished as they are being used so will not run out
Examples of renewable resources
Bio-fuels, solar, wind, geothermal, wave, tidal, hydroelectric
Replenishing renewable resources
Human action, natural processes
Fossil fuels
Fuels formed from the remains of living organisms (coal, crude oil, natural gas)
Nuclear fuels
Radioactive materials used in nuclear reactors (uranium, plutonium)
Bio-fuels
Fuels made from plant and animal waste (wood; bio-diesel)
Resources used for transport
Fossil fuels, bio-fuels
Resources used for heating
Fossil fuels, bio-fuels, geothermal, solar
Resources used to generate electricity
Fossil fuels, nuclear fuels, bio-fuels, solar, wind, geothermal, wave, tidal, hydroelectric
Reliable (energy resource)
an energy resource that can supply enough energy to meet demand at predictable times
Examples of reliable resources
Fossil fuels, nuclear fuels, bio-fuels, tidal, hydroelectric and geothermal
Environmental impact
the damage to the environment caused by using an energy resource to produce electricity
Examples of environmental impact
Pollution, harmful waste products and loss of habitats
Pollution
Damage to the land, air or water caused by a toxic chemical or an object
Atmospheric pollution
Carbon dioxide released from burning fossil fuels and bio-fuels, sulfur dioxide released from burning coal
Carbon neutral
Burning bio-fuels can be considered a carbon neutral process because it releases the same amount of carbon dioxide into the atmosphere as the crops absorbed for photosynthesis when they were growing
Closed system
A system in which there is no net change to the total energy
Law of conservation of energy
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
Useful energy transfer
When energy is transferred by a device to energy stores we want
Wasted energy transfer
When energy is transferred by a device to energy stores we don't want
Dissipate
When energy spreads out and is transferred to energy stores into less useful forms
Dissipated energy
Energy which is wasted and is usually transferred to the surroundings, causing them to heat up
Lubricate
When a substance is used to reduce wasted energy transfers by reducing the friction between moving parts
Insulate
When a substance is used to reduce wasted energy transfers by reducing the amount of heat that is transferred to the surroundings
Thermal conductor
A material that allows charge or heat to pass through it easily
Thermal insulator
A material that does not allow charge or heat to pass through it easily
Thermal conductivity
The rate of energy transfer by conduction through a material
Conduction
Heat is transferred through a material due to vibrating particles colliding and transferring energy from one particle to another
Convection
Heat is transferred through a moving liquid or gas due to differences in densities
Radiation
Heat is transferred from a hot object due to the object emitting infrared (heat) radiation
System
An object or group of objects
Kinetic energy
The energy of a moving object
Heat (thermal) energy
The energy of the particles in an object due to its temperature
Light (radiant) energy
The energy carried by a light wave
Gravitational potential energy
The energy stored in an object when it is raised against gravity
Chemical energy
The energy stored in food, fuels and batteries
Sound energy
The energy released by vibrating objects
Elastic potential energy
The energy stored when an object is stretched or squashed
Electrical energy
The energy in moving charges or static electric charges
Nuclear energy
The energy stored in the nuclei of atoms
Magnetic energy
The energy stored when repelling poles are pushed together or when attracting poles are pulled apart
Doing work
The scientific way of saying that energy has been transferred
Energy
The capacity to do work
