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conservation of energy Flashcards

1
Q

What is the kinetic energy store?

A

Energy is transferred to the store if an object speed up and away from the store if it slows down

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2
Q

What is a thermal energy store?

A

Any object - the hotter is, the more energy it has in the store

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3
Q

What is the chemical energy store?

A

Anything that can release energy by chemical reaction

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4
Q

What is a gravitational potential energy store?

A

Anything in the gravitational field

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5
Q

What is the elastic potential energy store?

A

Anything that stretches, like springs, rubber bands, etc.

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6
Q

What is the electrostatic energy store?

A

Two charges that attract or repel each other

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7
Q

What is the magnetic energy store?

A

Two magnets that attract or repel each other

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8
Q

What is a nuclear energy store?

A

Atomic nuclei release energy from the store in nuclear reactions

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9
Q

How do you workout the kinetic energy store?

A

0.5 x mass (kg) x speed - squared (m/s)
KE = 0.5 x m x v squared

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10
Q

What happens to the kinetic energy if you double the mass?

A

The energy in the kinetic energy store doubles

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11
Q

What happened to the kinetic energy if you double the speed?

A

The energy in the kinetic energy store quadruples because of the speed squared

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12
Q

An object at a height has energy where?

A

Gravitational potential energy store

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13
Q

How do you calculate the gravitational potential energy? (GPE)

A

m x g x ch = GPE
mass (kg) x gravitational field strength (N/kg) x change in vertical height (m) = gravitational potential energy (joules)

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14
Q

What does conservation of energy mean?

A

Energy is not created or destroyed

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15
Q

How can energy be transferred through stores?

A

Mechanically
Electrically
By heating
By radiation

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16
Q

How can energy be transferred mechanically?

A

A force acting on an object e.g pushing, stretching and squashing

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17
Q

How can energy be transferred electrically?

A

A charge doing work e.g charges moving round a circuit

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18
Q

How can energy be transferred by heating?

A

Energy transferred from a hotter object to a colder object

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19
Q

How can energy be transferred by radiation?

A

Energy transferred by waves e.g energy form the sun reaching earth by light

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20
Q

Analyse the changes involved in the way energy is stored when a system changes, when an object projected upwards or up a slope

A

The object does work against the gravitational force, so the energy is transferred mechanically from the kinetic energy store of the object to its gravitational potential energy store.

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21
Q

Analyse the changes involved in the way energy is stored when a system changes, a moving object hitting an obstacle

A

The obstacle has energy in its kinetic energy store. Some energy is also transferred mechanically to the thermal energy stores of the obstacle and the moving object. The rest is carried away by sound.

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22
Q

Analyse the changes involved in the way energy is stored when a system changes, an object being accelerated by a constant force

A

Assuming there’s no air resistance, gravity does work on the object, so the object constantly accelerates towards the ground. Energy is transferred mechanically from the rock’s gravitational potential energy store to its kinetic energy store.

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23
Q

Analyse the changes involved in the way energy is stored when a system changes, a vehicle slowing down

A

Energy in the kinetic energy store of the car is transferred mechanically. (due to friction between the tyres and road), and then by heating, to the thermal energy stores of the car and road

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24
Q

Analyse the changes involved in the way energy is stored when a system changes, a kettle boiling water

A

Energy is transferred electrically from the mains to the heating element of the kettle, and then by heating to the thermal energy store of the water

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25
When there are energy transfers in a closed system, what happens?
There is no net change to the total energy in that system
26
When do mechanical processes become wasteful?
When they cause a rise in temperature and dissipate energy and heating the surroundings
27
Energy is only useful when?
When it is transferred from one store to a useful store
28
What does the energy is dissipated mean?
Energy is spread out - so enters is lost
29
Where is the input energy dissipated to?
Thermal energy stores of the surroundings
30
How does a motor lifting a load show energy transfer?
Energy usefully from its kinetic energy store to the kinetic energy store and the gravitational potential energy store of the load, but it also transfers energy mechanically to the thermal energy stores of its moving parts, and electrically to the thermal energy stores of its circuits. This energy is dissipated, heating the surroundings.
31
What does the conservation of energy principle mean?
Total energy input = useful energy output + wasted energy
32
How to calculate efficiency?
useful energy transferred by device (J) divided by total energy supplied to device (J) x 100
33
Efficiency can never be higher than what
1 or 100% because some energy is always wasted
34
What are two ways that reduce the amount of energy being wasted?
Lubrication and thermal insulation
35
How does lubrication reduce energy transferred
Through friction
36
How does lubrication reduce energy transferred by friction
Whenever something moves, there is usually at least one friction or force action against it. This transfers energy mechanically to the thermal energy store of the objects involved, which is then dissipated by heating to the surroundings. For objects that are touching each other, lubricants can be used to reduce the friction between the object surfaces when they move. Lubricants are usually liquids like oil so they can flow easily between objects and coat them.
37
How does insulation reduce the rate of energy transfer?
By heating
38
How does insulation reduce the rate of energy transfer by heating?
When one side of an object is heated, the particles in the hotter part vibrate more and collide with each other. This transfers energy from their kinetic energy stores to other particles, which then vibrate faster. This process is called conduction. It transfers energy through the object. Materials have a thermal conductivity.- it describes how well the material transfers energy by conduction. For example, metals have a high thermal conductivity and gases have a low thermal conductivity. In the building, lower the thermal conductivity of its walls, the slower the rate of energy transfer through them. Some houses have cavity walls, made up of an inner and outer wall with an air gap in the middle. The air produces the amount of energy transferred by conduction, because air has a very low thermal conductivity. Thicker walls help too - the thicker of the wall, the slower rate of energy transfer
39
What are non-renewable energy resources?
Fossil fuels and nuclear fuel
40
What are fossil fuels?
Natural resources that form underground over millions of years that are typically burnt to provide energy
41
What are three main fossil fuels?
Coal, oil and natural gas
42
Facts on fossil fuels
Cost to extract fossil fuels is low Nuclear power plants are costly to build Fossil fuels are slowly running out Create environmental problems
43
What are examples of renewable energy resources?
Bio- fuels Wind The sun Hydro-electricity Tides
44
What are some facts on renewable resources?
Never run out Most damage the environment but less than non- renewable resources Don’t provide much energy
45
Some facts on bio- fuels?
Renewable energy sources created from animal dung and plant products Supposedly carbon neutral Fairly reliable as crops take a relatively short time to grow and different crops can be grown all year round.
46
Information on the wind power as a energy source
Each turbine has a generator inside it - wind rotates the blades which turn the generator and produce electricity so there’s no pollution. Initial costs quite high but running cost minimal. They can be noisy, which can be annoying for people living nearby Only work when it’s windy
47
Informational on solar cells as an energy source
Solar cells are made from materials that use energy transferred by light to create an electric current. Solar power is often used in remote places. There is no pollution, but the costs are very high. They generate small amounts of electricity.
48
Hydro electricity as an energy source (information)
Producing hydroelectricity usually involves flooding a valley by building a big dam. Rainwater is caught and allowed out through turbines. There is a big impact on the environment due to the flooding of the valley impossible loss of habitat for some species. An advantage is that it can immediately respond to increase electricity demand . Costs are high
49
Tidal barrages as a source of energy
Tidal barrages are big dams built across the river with turbines in them. As the tide comes in, it fills up the estuary. The water is done let out through turbines as a controlled speed to generate electricity. - no pollution but they affect both access and can spoil the view as they alter habitat for wildlife - Tides are pretty reliable, but the height of the tides is variable and marriages don’t work when the water level is the same either side - Initial costs are high but there are no fuel costs and minimal running costs
50
Since the 21st century, what use has been decreased
Electricity as more people are more careful with energy use in homes
51
Why do we burn fossil fuels?
Oil like diesel and petrol is used to fuel cars Gas is used to heat homes and cook food
52
How have energy resources been chosen for their effect on the environment?
Call companies have a higher demand for electric cars is gradually increasing
53
The use of renewable resources is usually limited to what
Reliability and money
54
How are renewable resources limited by reliability and money, referring to reliability?
Research into improving the reliability and cost of renewable resources takes time and money. it may take years before improvements are made
55
How are renewable resources limited by reliability and money, referring to personal changes?
It can be expensive or impractical. Solar panels are quite pricey and electric cars need to be charged.
56
A 2 kg object is dropped from height of 10 m. Calculate the speed of the object after has fallen 5 m, assuming there is no air resistance. g = 10N/kg
Change in height = 5m GPE = 2 x 10 x 5 = 100 J KE = 100 (2 x KE = 100) / m (2 x 100) / 2 = 100m/s (square root now) 10m/s
57
Describe the energy transfers that occur when wind causes a windmill to spin
Energy is transferred mechanically from the kinetic energy store of the wind to the kinetic energy store of the Windmill
58
An electrical device wastes 420 J of energy when it has an input energy at 500 J. Calculate the efficiency of the device as a percentage.
500 - 420 = 80 Efficiency = 80/500 = 0.16 x 100 16%
59
Suggest one way to improve the efficiency of electric motor
Lubricate moving parts
60
The government is considering closing down a traditional coal fired power station. Explain the benefits and disadvantages of replacing the power station with a wind farm.
Wind farms produce no pollution, which is much better for the environment than burning coal. They are also cheap to run, as there are no fuel costs and minimal running costs. You would need a lot of space to put the wind on, as you need lots of turbines to get the same power as a coal power station. People nearby also might dislike the wind, because the wind farm spoil the view and can be noisy.
61
Give two reasons we do not currently use more renewable energy resources in the UK
- Building new power plants is expensive - People don’t want to live near new power plants

physics (8 decks)

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