Summary of energy

There are two main types of energy, those at work and those stored:

At work...

• electrical
• thermal
• sound
• kinetic

Stored...

• chemical
• gravitational potential
• elastic
• nuclear

Energy cannot be created nor destroyed, only transformed from one form to another:

 Ex.1: A girl cycles up a hill and freewheels back down.

Chemical energy (pedalling) - gravitational potential energy (gaining height) - kinetic energy (down hill)

 Ex. 2: A boy uses a catapult to launch a stone.

Chemical energy (pulling) - elastic energy (strain on catapult) - kinetic energy (stone moving)

Evaporation and Conduction:

Evaporation - a surface effect, when liquid water turns into water vapour. The particles differ in speed, the fast moving particles reach the surface and escape, heating the liquid makes the particles move faster thus there is more chance of them escaping which is why rate of evaporaition is faster. Wind also sweeps molecules away speeding up the process of evaporation.

e.g clothes drying on a hot, windy day

Conduction -  the trasnfer of heat through matter, solid liquid or gas. The matter doesn't move, the heat energy is transferred from one molecule to the next. Different types of matter can influence the speed of conduction.

e.g metal rod & drawing pins demonstration in class

Convection and Radiation:

Convection -  the transfer of heat in a fluid, (liquid/gas NOT SOLID) The heat is transferred by the matter itself moving.

e.g  a heater in a room sends warm air up the wall, across the ceiling and back down again allowing heat to circulate the room

Radiation -  the direct transfer of heat from one place to another via electro-magnetic waves, it doesn't need a medium to travel through. The shorter the wave length and higher the frquency of these waves the more dangerous they are. Radio waves are long and have low frequency but gamma rays are short and have high frequency.

e.g the Sun radiating energy towards the Earth

Fossil fuels are non-renewable:

They are formed over thousands/milions of years from decomposing biomass that has been compressed to form coal, oil and gas.

They are burned in factories to generate electricity, but at rate we are burning them, fossil fuels will eventually run out.

The poisonous fumes created by burning fossil fuels causes acid rain. Acid rain weathers buildings and damges wildlife. The gases also congrugate in the atmosphere and absorb the Sun's heat causing global warming.

As an alternative to burning fossil fuels we can use renewable sources of energy.

Renewable energy sources are an alternative to fossil fuels:

They won't run out and we can use electricity without exhausting the Earth's natural resources.

• hydroelectric - uses water to generate electricity

• solar - uses photocells to store the Sun's energy

• wind - powers turbines and creates electricity

• geothermal - pump water underground, is heated and turns into steam, the steam is used to generate electricity