# Core Science Physics- Heat&energy

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Heat and energy

Different forms of energy

Chemical- In any object which can burn or chemically react.
Kinetic- In any object which is moving.
Gravitational potential- In any object which is above ground level.
Elastic potential- In any object which has been stretched or compressed.
Heat- In any object which is hot.
Electrical- Carried by electrons in wires and electrical equipment.
Light- Carried by waves from (usually) very hot objects.
Magnetic- In any magnet.
Nuclear- Inside the nucleus of any atom.
Sound- Carried by waves from any vibrating object.

Conduction

When one end of a metal bar is placed in a flame, the atoms at that end vibrate faster. They nudge their neighbours into faster vibration. These nudge their neighbours etc. until the atoms at the other end vibrate faster. This means the other end is now hotter. Heat is then said to travel by conduction.

Decreasing conductivity:
1. Metals
2. Concrete
3. Glass
4. Plastics
5. Water
6. Gases
7. Vacuum

Convection

When a pan of water is heated, the water particles move faster. They move around in a larger volume. That part of the water expands and becomes less dense. Less dense water rises, taking the heat with it. Heat is then said to travel by convection.

The heat from the sun cannot reach us by conduction or convection since there are no particles in space. Instead it is carried by a wave called "infra-red radiation." Any object warmer than its surroundings will radiate/emitt some heat and cool down. Matt, black surfaces are best emitters, shiny, silvery surfaces are worst.
Any object in the path of radiation may absorb this and warm up. Matt, black surfaces are good absorbers, shiny, silvery surfaces are poor absorbers (but good reflectors.)

Insulating a home

Possible methods include:
Cavity wall insulation-- traps air in between two walls
Loft insulation-- adds another layer for the heat to pass through (harder to escape)
Double glazing-- traps air between two pieces of glass
Draught excluders-- prevents a convection current occuring
Hot water tank insulation-- more heat goes into the water (traps the air)

Payback time= Initial cost / Annual saving

Energy, efficiency and power

An object has energy if it is capable of applying a force onto another object and make it move.

The power of a machine is a measure of how quickly it uses energy.
power= energy used / time taken
(watts)    (joules)        (seconds)

Efficiency is the proportion of input energy that is usefully used.
efficiency= useful energy out / total energy in (x 100 if you want a %)

Energy sources
Renewable= a source of energy that renews itself quickly

Fossil fuels (coal, oil, gas)