Why can’t a charged particle accelerate to the speed of light? :)

Question: Why can't a charged particle accelerate to the speed of light? :)
- Keywords:
  light speed,
  subatomic
Asked by rabiasami to Emma, Jimmy, Janet, Niall, Simon on 18 Mar 2013.
- James Holloway answered on 18 Mar 2013:
  
  Particles with mass cannot reach the speed of light because they would need infinite energy to do so. This is a result of the Theory of Relativity.
  
  If you try to make them go the speed of light you’ll find that all the extra push you give them starts to make the particle heavier instead of faster, and you end up making a particle that is going very close to the speed of light and is very heavy.

Question: Why can't a charged particle accelerate to the speed of light? :)