Y8 Energy
WHAT IS ENERGY?
Energy is not a substance or an influence; it doesn’t exist physically or take up space or cause changes to happen.
Energy is a concept/accountancy tool which allows mechanical work to be done meaning it can only be transferred.
There are two main types of energy:
Kinetic – about the vibration of particles (eg: thermal, kinetic)
Potential – energy that is stored waiting to be used/having the potential to be used (EPE, GPE)
Energy cannot be created or destroyed and is measured in Joules (J)
Change in energy is referred to as ΔE (Δ means change in and E means energy.)
CONSERVATION VS CONVERSION
Energy conservation is the fundamental law that energy can't be created or destroyed, only transferred.
Energy conversion is the process in which energy transfers from one energy to another leading to work being done (eg. KE to EPE when stretching a spring).
ENERGY STORES
PHYSICAL CHANGE | ENERGY STORE |
Height | GPE |
Temperature | Thermal |
Velocity/Movement | KE |
Chemical composition | Chemical |
Shape of an object | EPE |
Amount of charge | Electrical |
ENERGY EFFICIENCY AND USEFUL/WASTED ENERGY OUTPUTS
Efficiency in simple terms is a measure of how good something is at achieving its designed goal.
Efficiency (η) = useful energy output / total energy input x 100%
The more efficient something is the more useful energy output will be transferred from the total energy input, which means a higher % of efficiency means that something is more efficient.
Energy efficiency cannot surpass 100% as it would require a useful energy output greater than the total energy input which is not possible as energy cannot be created.
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A useful energy output is the desired form of energy a device provides, a wasted energy output is energy that is produced from the input but not the desired form of energy the device provides.
For example, a light bulb has the energy input of electrical energy, has the useful output of light but has waste energy of thermal and sound.
Some devices are more efficient as their desired energy is easier to produce.
Some devices are less efficient than others as their waste energy is easier to produce than their desired energy.
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SANKEY DIAGRAMS
Sankey diagrams are essentially scaled arrow diagrams which represent energy with the width of an arrow showing the proportion of energy.
The steps to draw a Sankey Diagram is:
Define a scale
Draw our input energy making sure the width is scaled and the energy labelled
Draw the useful output coming directly across out of the right side (scaled and of correct efficiency and labelled)
Draw the wasted output energy/energies pointing towards the bottom right (scaled and labelled)
WORK DONE
Work done is the energy transferred when a force causes an object to move a certain distance in the direction of the force.
EQUATIONS: Work done = Force x distance ΔE = F x d
Work done is measured in Nm or J
Force is measured in N
Distance is measured in metres
Work done means that mechanical work is done; for mechanical work to be done a force must act on something that is moving or causing movement.
No movement means that no work will be done as the distance will be 0.
For work to be done the following criteria must be met:
Energy must be transferred from one type to another.
Force must move an object through a distance.
The force and the distance must be in the same direction.
Work is done if all 3 criteria are met.
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THERMAL ENERGY
The temperature of an object is the average kinetic energy of the particles.
The thermal energy of an object is the total energy the particles have.
Adding/removing particles will not affect the temperature, but the thermal energy and likewise heating/cooling particles will not affect the thermal energy but affect the temperature.
Something with a higher temperature is warmer and something with a higher surface area (more particles) will have a higher thermal energy.
(Eg: a spark has a higher relative temperature but lower relative thermal energy to a swimming pool.)
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When we heat up a solid or a liquid the particles start to vibrate more vigorously and if we heat up a gas the particles move at higher speeds.
In both cases, the particles are gaining kinetic energy.
If you make the particles in a given object move faster, you are increasing the temperature. If you add more particles with the same energy, the total thermal energy increases.