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# energy changes in a system, and the ways energy is stored before and after such changes

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what is a system

object or group of objects

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what happens when a system changes

changes in the way energy is stores

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how is energy transferred

it is transferred mechanically, electrically, heating, radiation

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energy can be stored as

1. chemical 2. kinetic 3. gravitational potential 4. elastic potential 5. thermal 6. nuclear

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can be transferred from one store to another as

1. heating 2. waves 3. electric current 4. a force acting

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conservation of energy

energy cannot be created or destroyed

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a closed system

is isolated - energy is not being transferred in or out of it. means that the total energy of closed system is always the same

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energy can be transferred

usefully, stored or dissipated, but cannot be created or destroyed.

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describe energy transfers in a closed system (examples)

no net change to the total energy

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describe how in all systems changes in energy is dissipated

so that it is stored in less useful ways. This energy is often described as being ‘wasted’.

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explain ways to reduce unwanted energy transfers

e.g lubrication and thermal insulation

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The higher the thermal conductivity of a material

the higher the rate of energy transfer by conduction across the material.

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useful energy

Useful energy is energy transferred to where it is required in the form that it is wanted.

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other form of energy

this is all wasted energy

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what is wasted energy

it spreads out into the surroundings

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what form is wasted energy

This is usually in the form of heat energy causing the energy changing device and its surroundings to become warmer. It is very difficult to ‘concentrate’ this energy again to make use of it.

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what is energy efficiency

is a measure of how usefully energy is converted by a device

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the useful energy output can never be greater

greater than the energy input the efficiency can never be greater than 1.0.

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percentage efficiency

x100

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what does bigger % mean

the more efficient the device is.

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sankey diagrams

¥ The width of the arrows represents the amount of energy. ¥ The diagram should show the same total energy coming out as going in.

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work done .

When a force causes an object to move through a distance work is done on the object. So a force does work on an object when the force causes a displacement of the object.

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work done equation

= force x distance moved along the kine of action of the force

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units for work done equation

work done, W, in joules, J force, F, in newtons, N distance, s, in metres

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1 joule = 1 newton-metre

One joule of work is done when a force of one newton causes a displacement of one metre.

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what can work done against friction forces on a object cause

rise in temp of the object

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work is done on an object

• when a force acts on an object and makes it move or accelerate.

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work done is the same as

energy transferred

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what is power

rate at which energy is transferred or the rate at which work is done

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equation for power

= energy transferred / time

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equation for power 2

work done / time

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units for power equation

power, P, in watts, W energy transferred, E, in joules, J time, t, in seconds, s work done, W, in joules, J

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what is an energy transfer of 1 joule equal to

power of 1 watt

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The amount of gravitational potential energy gained by an object raised above ground level can be calculated using the equation:

gpe = mass x gravitational field strength x height

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gpe equation units

gravitational potential energy, Ep, in joules, J mass, m, in kilograms, kg gravitational field strength, g, in newtons per kilogram, N/kg height, h, in metres, m

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why do objects have gpe

due to their height

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the higher the object

the more gpe it has

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the heavier the object

the more gpe it has

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kinetic energy equation

0.5 x mass x speed2

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units for kinetic

kinetic energy, Ek, in joules, J mass, m, in kilograms, kg speed, v, in metres per second, m/s

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what is kinetic energy

energy stored in a object because it is moving

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transferring kinetic to gpe

When object falls, gravitational potential energy is transferred to kinetic energy

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if no other energy is added to the system

the total energy is the amount of gravitational potential energy it has at the top.

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what happens when an object reaches the bottom

there is no gravitational potential energy; it has all been transferred to kinetic energy.

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the gpe at the top

is the same to kinetic at the bottom

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elastic potential energy =

0.5 x spring constant x extension2

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units for elastic potential energy

elastic potential energy, Ee, in joules, J spring constant, k, in newtons per metre, N/m extension, e, in metres, m

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what happens when a spring is stretched

it has energy stored as elastic potential energy

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change in thermal energy =

mass x specific heat capacity x temperature change

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units foe change in thermal energy

change in thermal energy, ΔE, in joules, J mass, m, in kilograms, kg specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C temperature change, Δθ, in degrees Celsius, °C

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what is specific heat capacity

amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

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what are the main energy resources available

fossil fuels (coal, oil and gas), nuclear fuel, bio-fuel, wind, hydroelectricity, geothermal, the tides, the Sun and water waves.

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what is renewable energy

one that is being (or can be) replenished as it is used.

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uses of energy

transport , electricity, heating

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## Other cards in this set

### Card 2

#### Front

what happens when a system changes

#### Back

changes in the way energy is stores

### Card 3

#### Front

how is energy transferred

#### Back

### Card 4

#### Front

energy can be stored as

#### Back

### Card 5

#### Front

can be transferred from one store to another as

#### Back

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