Physics Section 4: Energy Resources and Energy Transfer (COMPLETED)

A

Units

kilogram (kg),

mass

joule (J),

energy

metre (m),

metre/second (m/s),

metre/second2 (m/s2),

newton (N),

second (s),

watt (W)

time

acceleration

distance

speed

force

power

B

Energy transfer

energy transfers

Energy can change from one form to another, and frequently does.

examples

Chemical energy in food turns into kinetic energy for movement;

Electrical energy in a circuit turns into heat energy in a resistor;

Kinetic energy in your muscles turns into sound energy from you voice.

Elastic potential energy in a taught rubber band turns into kinetic energy when it sails through the air.

conservation of energy

Energy can never be lost, only transferred.

Energy will always carry on, just in a different form.

For example, when you switch on a light, you are not loosing energy from a battery (chemical), you are just converting it to light energy!

efficency

useful energy output / total energy input= efficiency

With all devices that aim to use energy for a reason, some of the energy put in to run it comes out as a non useful form of energy.

The more energy that comes out as useful, the more efficient the object is.

a light bulb wants to create light energy, but it creates heat at the same time.

heat Transfer

conduction

Conduction is when energy is passed from one particle to another via contact. For example heat is passed from your skin to a window when they touch.

convection

Convection is when particles with energy rise, the space they leave is filled by other particles. If the source of energy continues these new particles will also gain energy, they will then rise and the process will be repeated.

radiation

Radiation is when heat is transferred as infra red waves. These waves can travel through space and be conducted or reflected.

Convection is helpful as it distributes heat energy. This is useful in many situations, for example, a radiator in one place will be able to heat a whole room, as hot air will rise away from it creating a current of cool air to be heated.

Insulation

An insulator is something that is bad at conducting.

If something with heat energy is surrounded by an insulator, it wont lose heat by conduction.

in buildings where insulating materials are put in walls and on floors to stop heat being lost from inside.

This is the same in humans where we wear clothes to stop heat being lost from conduction.

Air is a poor conductor, so materials with many air gaps in are also poor conductors; air trapped between double glazing prevents heat loss through windows.

C

Work and Power

W = F × d

work done = force × distance moved

Work done and energy transferred are always the same.

GPE = m × g × h

gravitational potential energy = mass × g × height

KE= 1/2 × m × v²

Kinetic energy = 1/2 x mass x velocity²

Conservation of energy (GPE and KE)

The best way to explain this idea is with a swinging pendulum:

At the top of the swing, it will have its highest gravitational potential energy (as its further from the earth); but it will have its lowest kinetic energy (it slows to a stop at the top point).

At the bottom of the swing, it will have its lowest gravitational energy (as it is closer to the earth); but it will have its highest kinetic energy (it goes very quickly past the bottom point).

Between the points work (force x distance) is constantly being done: the pendulum is moving through space.

Remembering that work done is equal to energy transferred, we can see that as work is done that moves the pendulum upwards, kinetic energy is transferred in to gravitational potential energy. When work is done to bring the pendulum downwards, energy is transferred from GPE to KE.

The pendulum demonstrates that energy is conserved, as then energy is constantly changing between different forms. The only reason that energy is lost from the pendulum, and it slows down, is that some energy is transferred into heat or sound.

Power

Power is the rate of work,

Power is also the rate of energy transfer.

So power is how quickly these processes are done.

Power= work/ time

P=W/t

D

Energy Resources and electricity generation

energy transfers- generation

wind

the kinetic energy from the wind, turns a turbine which turns a generator which produces electrical energy

water

Kinetic energy from water, turns a turbine which turns a generator which produces electrical energy

geothermal

Thermal energy heats water, water turns into steam, the thermal energy of the steam turns a turbine which then has kinetic energy, the turbine turns a generator which produces electrical energy

solar

solar heating

Light energy from the sun into thermal energy in water

solar cells

convert light energy from the sun into electrical energy

fossil fuels

Chemical energy is burnt to form heat energy, this turns into heat energy in water, this turns into kinetic energy in a turbine, this turns into electrical energy in a generator.

Nuclear power

kinetic energy in uranium, heat energy in water, kinetic energy in turbine, electrical energy in generator.

Advantages/ disadvantages

Fossil Fuels

disadvantages

non renewable

release CO2

Burning Wood

disadvantages

release CO2

Destroys habitats

advantages

renewable

HEP (Hydro electric power)

Wind Power

disadvantages

visual pollution

low electricity to space ratio

disadvantages

expensive to set up

limited locations

can damage fish/ water life

solar cells

disadvantages

rely on weather

nuclear power

disadvantages

toxic waste

dangerous