• Question: What does E=MC2 mean?

    Asked by benj807 to Alexander, Josh, Serena, Stuart on 17 Jun 2013.
    • Photo: Josh Makepeace

      Josh Makepeace answered on 17 Jun 2013:

      Einstein’s famous equation!! For ages I knew the equation, but didn’t know what it meant. I’m not a physicist, but I’ll give you my best go at an answer.

      The E in the equation means energy. Energy exists in the world in lots of different forms, for example there’s the energy that you have when you’re moving (that’s called kinetic energy), heat is energy, andthere’s also chemical energy locked up in molecules, which is how you get energy from food. There are lots of different types 🙂

      The m means mass (the amount of something!). What Einstein realised is that mass is just another form of energy, so you can turn a bit of something’s mass into another form of energy. That’s actually how a nuclear power plant works, it splits one element into two smaller ones, and a bit of their mass gets turned into energy, which gets used to make electricity.

      The equation E=mc2 lets you work out how much energy is contained in a certain amount of mass. So you multiply the mass by c (which is the speed of light) squared, to get the energy. Maybe one of the others know why you multiply by the speed of light squared? I certainly don’t!!

    • Photo: Stuart Archer

      Stuart Archer answered on 17 Jun 2013:

      To follow on from Josh’s excellent answer:

      The equation comes from Einstein’s theory of relativity. One of the most (relatively) basic concepts is that mass and energy are equivalent i.e. by measuring the mass of something you know how much energy it contains. The letter ‘c’ in the equation is a constant value that lets you work out one if you know the other.

      It’s really difficult to describe where it comes from without going into the maths of how Einstein’s theory of relativity works (it’s to do with how things move in the three dimensional world we kn0w relative to how they move in a ‘fourth’ dimension, which is basically just time). The value of ‘c’ (about 300,000 kilometers every second) is essentially the fastest speed that anything can move in space or time, and it just happens to also be the same as the speed of light.

      Hope this hasn’t confused even more!

    • Photo: Alexander Munnoch

      Alexander Munnoch answered on 17 Jun 2013:

      Energy(Joules) = Mass(kilograms)*C(the speed of light (metres/second)^2

      So 1 kg (e.g. 1L of water) of could be converted into:
      1* (3*10^8)^2 =
      9*10^16 Joules.
      1 calories = energy required to heat 1 gram of water by 1’C = 4.2 joules.

      So…
      (9*10^16 Joules = 2.1*10^16 calories = 2.1*10^13 kilocalories)

      and if Loch Ness has a water content of approximately
      7.5*10^13 litres

      Then…
      by converting about 3L of water into energy, it would be enough to raise the temperature of the whole of Loch Ness’ water by 1’C!

      Wee extras of info:
      It is worthwhile saying that the speed of light is about 3×10^8m/s in a vaccuum and not air, liquids or solids (all of which it is slower through).

      Published by Albert Einstein (although he didn’t get the 1921 Nobel prize in physics for this – he got it for his work on the photoelectric effect where you can generate electricity by shining UV light on a metal surface!)

Comments