Energy in Food
We get our energy from the food we eat. The energy is released
by combustion or respiration in our cells. The amount of energy
is usually shown as calories, however, the scientific term for
energy is joules. There is a very large amount of energy in food,
so food labels often show the energy in kilojoules (kJ).
1000J = 1kJ
Different types of food have different amounts of energy, for
example, an éclair has about 3140 kJ per 100g, whilst a peach
has 135 kJ per 100g.
Brisk walking uses up about 14 kJ per minute, so 100g of
peaches would give you enough energy for about 9.5 mins of
Electrical power is the rate at which energy is transferred.
Power is measured in Watts (W). 1 Watt is 1 Joule per second,
which means a 20 W bulb uses 20 Joules per second.
Electrical appliances usually display their power on the label.
Some appliances that use a lot of energy display their power
in kilowatts (kW).
1000 W =1kW
Electric companies use kWh instead of joules, which is the
amount of energy used by a 1kW appliance in one hour.
Where does energy come from?
We get energy from non-renewable and renewable energy
sources. Most of the energy comes from fossil fuels, which
are a non-renewable energy source.
Fossil fuels were formed millions of years ago from dead
organisms. Coal was formed from dead plant forms, crude oil
and gas were formed from dead marine organisms.
Fossil fuels are a finite energy source as they are being used
up quicker than they can be remade. There is only a limited
amount of fossil fuels in the world.
Most of the electricity in the UK comes from fossil fuels. The
fuels are com busted, creating heat energy which is used to
boil water. The steam turns turbines which then turn electrical
generators. The burning of fossil fuels releases gases into the
air which amount to pollution. The main gases produced from
burning fossil fuels are carbon dioxide (which is a greenhouse
as that increases global warming) and sulphur dioxide and
nitrogen oxides (which cause acid rain, killing plants and