Earth and beyond

Earth's energy resources

non-renewable energy sources

renewable energy sources

sources of energy in the world

unusual sources of energy

measuring work and energy

the greenhouse effect

nuclear power

trapping the Sun's energy

using solar cells

Sun and climate

measuring work and energy

Energy is the ability to do work. This applies to humans as well as to objects. If you've got a lot of energy, you can go clubbing. If you've got no energy, you just feel like slumping down in a chair and watching TV.

Sometimes when energy is transferred, a force acts which moves something: lifting a book, cycling uphill, walking up stairs, kicking a football. The word 'work' in science has a special meaning. We say that work is done on an object when a force moves that object.

Getting to grips with the amount of energy.

Image of James Prescott Joule

James Joule

The unit in which energy is measured is called a joule (J). The amount of energy (in joules) transferred per second is measured in watts (W). One watt is therefore the transfer of one joule every second. Power stations output many megawatts (millions of watts).

Take a look at this table of energy and compare the different amounts of energy produced.

Image of James Watt

James Watt

	joules
Energy to lift a book from the floor to the table	1
Energy of a bullet leaving a gun	1000
Average energy used by your body in a day	10⁷
Energy provided by 1 gallon of petrol in a car	10⁸
Energy from 1 ton of coal	10¹⁰
Energy in a hurricane	10¹⁵
Energy received on Earth from the Sun each second	10¹⁷
Energy of a severe Earthquake	10¹⁸
World energy consumption in a year	10²⁰
Energy received on Earth from the Sun each day	10²¹

Image of the Sun taken by YOHKOH Every second, the Sun radiates 4 x10²⁶ J of energy.
That's 400,000,000,000,000,000,000,000,000 joules per second or

400 billion billion megawatts!

Only a small fraction of this energy actually reaches the Earth (about 2x10¹⁷ joules each second), but that's still a vast amount of energy. All the power stations in the world put together produce less than 0.4% of that!



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