where
E = energy (in joules)
m = mass (in kilograms)
c = speed of light
(300,000,000 meters per second)
Notice the resemblance to the kinetic energy equation shown earlier.
Energy cannot appear without the disappearance of mass. When energy is
locked up in a fuel, it is stored as mass. In the gasoline combustion
problem, 1 gram of gasoline was burned with air to give 48,000 joules of
energy. Einstein’s equation says that in this case mass disappeared in
the amount
m = E/c² = (4.8 × 10⁴)/(9 × 10¹⁶) = 5.3 × 10⁻¹³ kilogram
(half a billionth of a gram)
But, when an H-bomb is exploded, grams and even kilograms of mass are
converted to energy.
In direct conversion processes we do not need to worry about these mass
changes, but at each point we must make sure that all energy is
accounted for. For example, in outer space all energy released from
fuels (even food) must ultimately be radiated away to empty Space.
Otherwise the vehicle temperature will keep rising until the Spaceship
melts.