The mass of the proton was determined in a similar way to how the mass of atoms are
measured.
The particle, whose mass is being determined, is accelerated through an electric field, the
particle then passes through a perpendicular magnetic field which deflects the particle (particle must be charged, a proton or an ion for example, for it to deflect). The
angle by which it deflects is dependent on the mass of the particle. The mass of the particle can be determined by using the following formula:
Centripetal Force = Force due to magnetic field(B)
(mv2)/r = Bqv
(where m = mass of particle, v = velocity of particle, r= radius of deflected path, B =
magnetic field strength, q = charge of particle)
Answered by: Simon Hooks, Physics A-Level Student, Gosport, UK
'The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative... '