Asked by: Alper Akyurek

As the speed of the object is increased, the inertial mass of the object also increases. For speeds significantly less than the speed of light, the increase in mass is nearly imperceptible, but as the speed of light is approached, the mass starts to increase very rapidly toward infinity. Theoretically, the mass would become infinite if the object could be accelerated all the way to the speed of light. However, because the acceleration of an object in response to a given force is inversely proportional to its inertial mass, as the speed of light is approached the force required actually to reach the speed of light also becomes infinite. Therefore, it is impossible actually to accelerate an object with non-zero rest mass to the speed of light.

Another way of expressing the fact that a massive object cannot be accelerated to the speed of light is through the concept of energy. That is, an infinite amount of energy would have to be expended, via the accelerating force, to reach the speed of light.

So, quite simply,

Answered by: Warren Davis, Ph.D., President, Davis Associates, Inc., Newton, MA USA

Mass measures the amount of inertia an object has, with inertia defined as the resistance the object offers to a change in its state of motion. While we usually think of mass as being constant for an object, Relativity tells us that energy and mass are interchangeable. Any object in motion has, by definition, Kinetic Energy. That energy has the effect of increasing the object's mass,

Mathematically, an object's true mass is given by the expression:

where

You can see that when

Since c is over 186,000 miles/second, we are not accustomed to dealing with objects travelling at velocities high enough to have a mass noticeably greater than their rest mass. Experiments with subatomic particles, however, confirm Relativity's prediction of increasing mass at speeds near c. Devices from particle accelerators to TV picture tubes must account for mass increase in order to work properly.

Answered by: Paul Walorski, B.A. Part-time Physics Instructor

'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... '**Michio Kaku**

(*1947-*)

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