Energy
There are about 20 million households in Britain alone and on
average each one of these uses some 21 000 kW h of energy annually! The study of energy
is therefore of vital importance in our lives.
World energy use
An account of the growth in world
energy consumption makes sobering reading. If we define a quantity of energy (Q) as
1021J then in the 2000 years up to 1850 the world is thought to have used
between 6 and 9 Q. In the following hundred years up to 1950 it had burned a further 6 Q
and from then on we have been using at least 1Q every ten years. Fortunately in recent
years this rate of increase has slowed down considerably, partly because of the high cost of
energy.
Energy conservation is also important. Some 5 per cent of the total energy bill of
the western world can be saved by conservation measures such as the proper use of
insulation!
To give you some idea of the value of energy, the table below shows the
energy used in a number of situations.
| Typical energy values (J) |
Joules |
| moonlight on face for 1 s |
10-3 |
| pressing down a typewriter key |
1 |
| house brick raised to shoulder height |
30 |
burning a match |
1000 |
| potential energy of a person at the top of the stairs |
1500 |
| kinetic energy of a car travelling at 70 mph |
500000 |
| electrical energy in a fully charged car battery |
2000000 |
| chemical energy in a day's food intake |
11000000 |
| chemical energy in one litre of petrol |
35000000 |
| first atomic bomb |
1013 |
| very severe earthquake |
1020 |
| world annual energy consumption (2008) |
4.74x1020 |
| Earth's annual share of the Sun's heat |
1025 |
| Rotational kinetic energy of the Earth |
1029 |
Relative present energy use per person per day
| USA |
10 000 |
| Japan and Europe |
4000 |
| Less developed countries |
100-1000 |
| World average |
2000 |
Simple estimate of the world's annual energy consumption
Total =
5x10
9 people x 2000W x 86400x365 = 315x10
18 = 3.15x10
20
J
Conservation of energy
You should notice that we talk about the
transformation or conversion of energy from one form to another and not its use. This is
because although we may use up energy in one form it always reappears as another. This is
a most important principle of Physics: that of the conservation of energy. The principle states
that:
Energy is never created or destroyed but only changed from one form to another.
The
enormous increase in demand for energy this century makes the production and conversion
of energy a most important topic. But you may ask: why worry, if energy is always
conserved? The trouble is that it is changed from useful or high-grade forms such as
chemical or electrical energy to relatively useless forms such as low-grade
heat.
Ultimate recoverable energy deposits (thousands of millions of
tonnes or equivalent)
| |
Cumulative production to 1975 |
Proven or probable reserves |
Possible additional reserves |
| Petroleum |
48.4 |
114.8 |
142.7 |
| Tar sands |
0.025 |
300 |
|
| Shale oils |
- |
460.3 |
1415.6 |
| Natural gas |
21 |
54 |
185 |
| Charcoal |
n/a |
339.9 |
4904 |
| Lignite |
n/a |
99.3 |
1656 |
| Total |
n/a |
1368.3 |
8303.3 |
(Interdisciplinary Science Reviews 1983)
| Oil |
60 year supply remaining |
| Natural gas |
100 years supply remaining |
| Coal |
200 years supply remaining |
| Uranium |
200 years supply remaining |
| Fusion |
1 million years supply remaining |
| DD Fusion |
10 billion years supply remaining |
(See also Energy sources)
A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS USB
