Question

For a particle to travel with speed of light, what should be the mass?

Answer 1

As the velocity of an object approaches the speed of light the mass of the object approaches infinity.

Answer 2

I thought Mass is a constant. Why the mass varies depending on time or velocity? Is it balancing something?

Answer 3

\[m={m_0 \over \sqrt{1-({v^2 / c^2})}}\]where
m=the effective mass of the object, which is dependent on its velocity
m_0=the mass of the object at rest
c=the speed of light (3x10^8m/s)

Answer 4

The flow if time, the spatial dimensions, and the mass of an object in motion all change in order to keep the speed of light constant for all frames of reference. The actual mathematics is needed to demonstrate how this happens, but it has to do with the fact that the speed of light is ALWAYS measured to be c, no matter what velocity the observer is moving relative to it's source.

Answer 5

In short, special relativity teaches us that space, time, and mass are dependent on the velocity of the observer, i.e. they are not constant for all frames of reference. Thus they are, in a sense, subjective. Or at least not absolute.

Answer 6

okay we know kinetic energy is [(1/2)*m*v ^{2] i have a mass of 1kg and i want it to travel at the velocity of light, so the energy required will be calculated from above equation. If i provide that, won't the object move at the velocity of light?

Answer 7

No the equation you have is not at all relativistic. The one you are using is for Newtonian Mechanics, which does not take into account the fact that c is constant for all frames of reference. The actual equation you want is more complex, and is of the same form as the one for mass, such that as the velocity of the object approaches the speed of light , it's energy will approach infinity.
http://en.wikipedia.org/wiki/Special_relativity
(look at the section on Kinetic Energy)
It can also be stated that if the mass goes to infinity, as I mentioned above, it takes an infinite force to accelerate it. This illustrates the same concept: infinite energy is required to accelerate any mass to the speed of light.

Answer 8

If you are taking a high school or introductory college physics course, Newtonian mechanics is what you will be using. It's only when dealing with more extreme concepts, like objects moving close to the speed of light, that relativistic equations are necessary.

In everyday circumstances Newtonian Mechanics provides a good enough interpretation of reality to be used,, but Relativity overthrows the laws of Newton and is a better model for nature in cases like the one you describe.

Answer 9

to travel at the speed of light requires a rest mass of zero

Answer 10

Exactly what Rhaukus says.

For example, photons travel at the speed of light and their imputed rest mass is zero.