Mass & Energy

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Mass and Energy Equivalence

Mass and energy can be shown to be equivalent.

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Mass varies with speed

  • As an object gains velocity, it also gains mass.
  • This is given by the formula:
    • m=m01v2c2m = \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}
    • m is the moving mass.
    • m0m_0 is the mass at rest.
    • v is the moving velocity.
    • c is the speed of light.
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Einstein's relativity

  • Einstein extended relativistic mass to produce:
    • E=mc2E = mc^2.
  • This shows that mass and energy are equivalent.

Bertozzi's Experiment

Bertozzi’s experiment sought to provide experimental proof that mass increases with velocity.

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  • Bertozzi used linear particle accelerators to accelerate electrons into an aluminium disc.
  • He recorded the time taken for the electrons to reach the disc, along with the energy provided to the electron.
  • He used the heat generated on the aluminium disc to calculate the final velocity of the electrons.
    • He did this by equating heat and kinetic energy.
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  • He found that the velocities of the electrons did not continue to increase as he supplied more energy to the electrons.
  • Instead, they approached a maximum value of c - the speed of light.
  • This is the first evidence of special relativity.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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