(c) Work and power
4.9 know and use the relationship between work, force and distance moved in the direction of the force:
Energy is the ability to do work.
work=force x distance
W=F x d
1J of work is done when a force of 1N is applied through a distance of 1m in the direction of the force.
4.10 understand that work done is equal to energy transferred
Doing work means the energy is either decreased or increased. If a weight of 500N is raised 2m, 1000J of work is done. That means energy is increased by 1000J. Therefore work done is equal to energy transferred.
4.11 know and use the relationship:
The energy that the weight has gained is called gravitational potential energy.
gravitional potential energy=mass × gravitional acceleration × height
G.P.E=mgh
4.12 know and use the relationship:
Kinetic energy = ½ x mass x velocity2
K.E = ½ x m x v2
4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
An object of mass,m weights mxg newtons. So the force,F, needed to lift is mg. If we raise the object through a distance h, the work done on the object is mgh. This is also the gain of GPE.
When the object is raised, it falls-it loses GPE but gains KE. At the end of the fall, all the initial GPE is converted into KE. And that’s how energy is conserved.
work done lifting object=gain in GPE=gain in KE of the object just before hitting the ground
4.14 describe power as the rate of transfer of energy or the rate of doing work
Power is the rate of transferring energy or doing work. Its measures how fast energy is transferred. The Watt is the rate of transfer of energy of one joule per second.
4.15 use the relationship between power, work done (energy transferred) and time taken:
power=work donetime
P=Wt
(d) Energy resources and electricity generation
4.16 describe the energy transfers involved in generating electricity using:
- Wind: Winds are powered by the Sun's heat energy. Wind is a renewable source of energy. Wind mills have been used to grind corn and power machinery like pumps drain lowland areas. Today, wind turbines drive generators to provide electrical energy. Here, kinetic energy is transformed to electrical energy.
- **Water:**Water is used to generate energy in three ways: Hydroelectric power, Tidal power & Wave energy. All the ways uses the same role using the movement of water(K.E.) to rotate that generator and produce electricity. In this casekinetic energy is also transformed to electrical energy.
- Geothermal resources: Geothermal energy is heat energy stored deep inside the Earth. The heat in regions of volcanic activity was produced by the decay of radioactive elements. The heated water from the earth’s crust is used to rotate turbines in generator. Here, heat energy is converted to kinetic energy which is converted to electrical energy.
- Solar heating systems: Solar heating panels absorb thermal radiation and use it to heat water. The panels are placed to receive the maximum amount of the Sun’s energy.This produce steam which can be used to drive electricity generators.
- Solar cells: Solar energy directly converts light energy into electrical energy.
- Fossil fuels: Fossil fuels are natural gas, oil and coal. Those are burned which rotates the turbine in the generator to produce electricity.
- Nuclear power: Nuclear fuels like uranium are used in nuclear generator. The heat produced in nuclear reaction is used to produce steam from water which rotates the turbine and produce electricity.
4.17 describe the advantages and disadvantages of methods of large- scale electricity production from various renewable and non- renewable resources.
Renewable Resources:
| Advantages | Disadvantages | |
|---|---|---|
| Wind energy | - Relatively cheap to set up - Clean – no waste products - Relatively efficient at converting energy into electricity | - Only produce energy when it is windy - Can be used only in certain places - Can be an eyesore - Can produce noise pollution - May kill birds and bats |
| Wave energy | - Continuously available - Clean - no waste products - Moderately efficient | - Expensive to set up - Only suitable in certain locations |
| Tide energy | - Continuously available - Clean – no waste products - Efficient | - Damaging to environment - Expensive to set up - Only suitable in certain geographical locations |
| Solar energy | - Clean-no waste products | - Expensive in terms of amount of energy produced - Not very efficient method - Energy supply is not continuously available - Best suited to climates with low amounts of cloud cover |
| Geothermal energy | - Clean- no waste products - Can provide direct heating as well as heat/steam to drive electricity generators - Moderate start-up costs | - Suited only to geographic locations with relatively thing ‘crust’ or high volcanic activity |
| Hydroelectricity | - Clean – no waste products - Continuously available | - Needs large reservoirs, which may displace people or wildlife - Can be built only in hilly areas with plenty of rainfall |
| Biomass | - The carbon dioxide it releases when it burns has only recently been taken out of the atmosphere by crops | - Growing biomass crops instead of food can cause food shortages. |
| Wood | - With careful management, the supply of wood fuel can be maintained indefinitely. | - Produces pollution and greenhouse gases. - Wood is more valuable in other sectors rather than producing energy, such as furnitures and buildings. |
Non-Renewable Resources:
| Advantages | Disadvantages | |
|---|---|---|
| Fossil Fuels | - Readily available - Easy to produce | - Burning fossil fuels produce greenhouse gases which lead to global warming. - Sulphur causes acid rain. |
| Nuclear fuel | - Reliable, clean and efficient. - Cost of electricity is low. | - Expensive to build. - Dangerous. |