Physic Labs

Theory of relativity

Mass–energy equivalence

Relate mass change to rest energy, ΔE = Δm c², and distinguish conservation conditions in the simulated processes. Measure energy change and equivalent mass, then verify E=mc2E = mc².

Undergraduate

⚠ Mass–energy conversion and particle reactions here are conceptual simulations; do not handle radiation sources.

Equipment

  • Absorbing-body model and photon conversion into an e⁻e⁺ pair
  • Logarithmic energy E and body-mass M sliders; process selector

Procedure

  1. Compare two conversion processes

    In Absorbing energy mode, adjust E and M with the logarithmic sliders; inspect the equivalent mass Δm = E/c² and note the sign to distinguish absorption from energy release. Switch to Photon creates e⁻e⁺ pair and raise E through the pair-production threshold 2mₑc² = 1.022 MeV to examine the minimum-energy condition. The conversion illustrates energy–momentum conservation; a single photon cannot create a pair by itself in vacuum. Compare the displayed values with E=mc2E = mc².

  2. Check the equivalent mass

    In energy-absorption mode, vary E across slider settings and record displayed Δm. Calculate independently with Δm=E/c2\Delta m = E/c^2; check that equivalent mass rises proportionally with added energy.

  3. Check the pair-production threshold

    Select photon mode and raise E from below to above 2mec22m_ec^2. Record when the simulation indicates sufficient energy; explain why the rest energy of both particles and momentum conservation matter.

Simulation

Experiment history

In 1905 Albert Einstein published special relativity and, in a short subsequent paper, argued that energy emitted as radiation reduces a body's mass by a corresponding amount. The relation is often summarized as E = mc², where c is the speed of light; it means that rest mass represents rest energy, not that mass can be converted into energy without constraints. Twentieth-century nuclear and particle physics confirmed the central role of mass–energy relations in reactions and decays. Electron–positron pair production requires at least the combined rest energy 2mₑc² as well as momentum conservation; a lone photon cannot create a pair in empty space. The simulation illustrates these principles conceptually and does not represent a real particle reaction.

Related physicists

Albert Einstein

Related library topics

Relativistic momentum and energy, E = mc²The equivalence principle