1. Mass and Energy
E=mc2 and all that

2. MASS and REST MASS
In 1905 Einstein showed that the mass of a moving object, as measured by a stationary observer, increases as it approaches the speed of light.
This effect is important for fundamental particles which can be accelerated to very high velocities.Therefore we use the term rest mass (m0) of the particle to mean the mass of the particle when it is stationary ?

3. The energy equivalence of mass
We can talk abou the rest mass and the rest energy of a particle interchangeably.
However the units are awkward because they are so small
It is convenient to have another unit for energy in particle physics
particle
Rest mass (m0/kg)
Rest Energy (J)
electron
9.11x10-31
8.20x10-14
proton
1.67 x 10-27
1.50 x10-10

4. Units of Energy ----------------------------------------------
A negatively charged free electron is accelerated from a negative electrode towards a positive electrode and in doing so gains kinetic energy.
The amount of kinetic energy it acquires ,just before it strikes the anode is called 1 electron volt.
Potential difference of 1 volt
An electron volt is a tiny quantity of energy 1eV=1.60 x10-19J

5. The mass equivalent of the electron is 8.20x10-14J
Which is the same as
8.20x10-14 ÷ 1.60x = eV
particle
Rest mass (m0/kg)
Rest Energy (J)
Rest Energy (MeV)
electron
9.11x10-31
8.20x10-14
0.511
proton
1.67 x 10-27
1.50 x10-10
938
These more sensible numbers are often used directly in calculations.

6. The unified atomic mass unit
The unified atomic mass unit (u) is defined as of the mass of a atom.
On this scale the normal hydrogen atom has a mass of
The oxygen-16 atom is etc
1u = x 10-27kg = 931.5MeV