Physics: Energy

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What is a system?
A system is a an object or group of objects.
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Examples of changes in the way energgy is stored when a system changes.
An object projected upwards, a moving object hitting an obstacle, an object accelerated by a constant force, a vehicle slowing down and bring water to boil in a kettle.
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Describe all the changes involved in the way energy is stored when a system changes.
When a system changes energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy store.
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Calculate the changes in energy involved when a system is changed by heating, work done by forces and work done when charge flows?
Energy can be transferred by heating. For example water being boiled in a kettle, energy is transferred to the water by heating into the water's thermal energy store. Energy is also transferred electrically. Work can be done when current flows or by
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How do you calculate the kinetic energy of a moving object?
KE = 05 x mass x speed ^2
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How do you calculate the elastic potential energy gained by an object raised above ground level?
elastic potential energy = 0.5 x spring constant x extension^2
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How do you calculate the amount of gravitational potential energy gained by an object raised above ground level?
g.p.e = mass x specific heat capacity x temperature change
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How do you calculate the amount of energy stored in or released from a system as it temperature changes?
change in thermal energy = mass x specific heat capacity x temperature change
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What is the specific heat capacity of a substance?
The amount of energy required to raise the temperature of 1kg of substance by 1 degree celsius.
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Power
The rate at which energy is transferred or the rate at which work is done.
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What is the equation to calculate power?
power = energy transferred / time and power = work done / time
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What is the energy transfer of 1 Watt?
1 Watt = 1 Joule per second
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Example of the definition of power.
Take 2 cars that are identical in every way aart from the power of their engines. Both cars race the same distance along a straight line track to a finish line. The car with the most powerful engine will reach the finish line faster than the other ..
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continued....
car - ie. it will transfer the same amount of energy but over less time.
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Energy transfers
Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed.
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Closed Systems
Closed systems are systems where neither matter nor energy can enter or leave. The net charge in the total energy of a closed system is always 0.
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Dissipated Energy
Dissipated energy is sometimes called wasted energy because the energy is being stored in a way that is not useful. For example a mobile phone system, energy is usefully transferred from the chemical energy store, but some energy is wasted as thermal
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What are methods of reducing dissipated energy?
The use of energy saving batteries and bulbs or low wattage items. Lubrication and thermal insulation.
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Lubrication
Lubrication reduces frictional forces, whenever something moves there is usually at least one frictional force causing energy to be dissipated, lubricants like oil can make objects flow more easily between objects.
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Thermal Insulation
Insulation reduces the rate of energy transfer by heating. Thick walls made from a low thermal conductivity material, the thicker the walls and the lower the thermal conductivity the slower the rate of energy transfer.
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How do you calculate energy efficency?
Efficiency = Useful output enrgy transfer / Total Input energy transfer Efficiency = Useful power output / Total power input
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What are the main energy resources avaliable for use on Earth?
Fossil fuels (coal, oil, gas), nuclear fuel, bio-fuel, wind, hydroelectricity, geothermal, tidal, Sun and hydroelctric.
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What are renewable energy sources?
Renewable energy is energy that is collected from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat.
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What are the uses of energy resources?
Transport, electricity generation and heating.
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Why are some energy sources more reliable than others?
Because they are more avaliable, eg solar is reliable in hot sunny countries but not very reliable in the UK.
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What is the environmental impact arising from the use of different energy resources?
Non-renewable enrgy releases CO2 into the atmosphere when burnt and they cant be replaced. Renewable enrgy resources are usually expensive and can be noisy and cause other types of pollutions when gathering energy or in the manufacturing process.
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Describe the trend in the use of energy resources.
As the amount of precious fossil fuels decreases and we gain more awareness of the dangers of the use of fossil fuels, the use of renewable energy sources increases.
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Other cards in this set

Card 2

Front

An object projected upwards, a moving object hitting an obstacle, an object accelerated by a constant force, a vehicle slowing down and bring water to boil in a kettle.

Back

Examples of changes in the way energgy is stored when a system changes.

Card 3

Front

When a system changes energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy store.

Back

Preview of the back of card 3

Card 4

Front

Energy can be transferred by heating. For example water being boiled in a kettle, energy is transferred to the water by heating into the water's thermal energy store. Energy is also transferred electrically. Work can be done when current flows or by

Back

Preview of the back of card 4

Card 5

Front

KE = 05 x mass x speed ^2

Back

Preview of the back of card 5
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