Getting the measure of energy

Energy is an abstract concept and it can be hard to get a feel for the quantity of energy transferred in different events. The table below gives the orders of magnitudes of energy transferred by a range of events in the universe:

Event	Energy transferred (J)
Big Bang	10 68
Typical supernova	10 44
Krakatoa eruption	10 18
Burning 1 L of petrol	3 x 10 7
Daily food intake of a human adult	2 x 10 7
Kinetic energy of a cricket ball hit for six	10 3
Work done by a human heart per beat	0.5
Work done in turning the page in a book	10 -3
Work done in discharge of a single neuron	10 -10
Typical energy of an electron in an atom	10 -18
Energy needed to break one bond in DNA	10 -20

When comparing fuels, it can be more useful to consider the amount of energy stored per unit mass (the energy density) rather than the absolute magnitude of energy transfer. A comparison of the energy densities of different fuels highlights the potency of uranium:

Fuel	Energy density (MJ/kg)
Uranium (in breeder reactor)	80,620,000
Hydrogen (compressed at 70 MPa)	142
Liquefied petroleum gas	46
Jet fuel	43
Fat (animal/vegetable)	37
Coal	24
Carbohydrates (including sugars)	17
Protein	17
Wood	16
TNT	4.6
Lithium battery (non-rechargeable)	1.8

Excluding nuclear blasts, perhaps the most energetic human-created explosion was a test carried out by American scientists in 1987, codenamed Misty Picture. In order to mimic the effect of a low yield nuclear weapon, the scientists detonated 4,685 tonnes of ammonium nitrate and fuel oil explosives at White Sands Missile Range in New Mexico. The explosion is estimated to have had a yield of 33.4 TJ (33.4 x 10¹² J).