Why does mass change with speed?

Question

It is learnt that mass does not change with change of position and place. Why should the mass change with change of speed of an object? Is it becouse of E=mc^2 alone or something else? The mass should not change with change of any kind. What is the true nature of mass?

Just tryng to understand it. If mass can converted into energy than energy must have a mass. If energy has a mass than it is a matter. The photon if it exist as told should not have its own force to propagate itself and "c" is caused some external source. If photon has no mass than it must be nothing but the force causing "c" itself. It therefore seems that mass doesnot change with speed and energy /force/power has shifting mass. I am not sure about the correctness of the above.

Answer 1

Don't be confused here, remember if you went from 'standing still' to going .99c, YOU would NOT measure your mass as changed. It is an outside observer who was still 'standing still' that would think your mass had changed. It isn't the E = mc^2 that does this, it is because the amount of work one would need to do to push you to speed you up an increment grows 'exponentially' as you approach the speed of light, beyond what one would expect if your mass was constant.

Answer 2

E=mc^2 is probably not the proper equation for this. The combined (potential + kinetic) energy for a given mass DOES NOT CHANGE, unless the mass changes. Nor does the mass of an object with an increase in speed. The increase in mass is simply an illusion created by the FORCE of an object. Since Instantaneous Force= Mass x Instantaneous Velocity, the speed of an object will affect its weight at that particular instant. A perfect way to test this is to stand on a scale, record your weight, then jump slightly, landing back on the scale, and notice for a brief second your weight will be significantly higher, which is an indication of the force exerted on the scale at the precise time.

Answer 3

You are right. Mass can not increase. Even though the mass can be converted to energy and proved in radiation and fusion the reverse is not proved. It is only a theory. But the hypothesis that when a mass reaches near the velocity of c ( speed of light) that the mass increases implies speeding up is a process that converts energy in to mass. Which is not true. What is true here that there is a conflict between the mathematics and physics. To balance the energy equation mathematician use an equivalent mass which is the mass + equivalent mass of the kinetic energy. In physics this doesn't happen. In fact the mass will reduce since the energy to accelerate the mass has to come from somewhere. It could be the mass itself. Like in rocket to speed up it uses the mass. Hence the as speed of rocket increases the mass will reduce. This process is not the same as the previous one. But somewhere that energy to accelerate the mass has to come from. Anyways even if we assume it is accelerated by a gravity pull then the mass will remain same. will not increase.

Answer 4

In more modern notation, the rest mass of an object does not change with its speed. What changes is the energy. The relativistic energy is

mc^2/sqrt[1-v^2/c^2]

where m is the rest mass.

The confusion arose because most people were accustomed to writing momentum as "mv" whereas the relativistic momentum
is

mv/sqrt(1-v^2/c^2).

Back in the day, people often attatched the denominator to the m, that is, they thought

momentum=Mv, M=m/sqrt(1-v^2/c^2),
energy=Mc^2.

Hence the "changing mass." But there are good reasons to think of the rest mass as unchanged--you stated some of them in your question.

In special relativity, mass is the invariant length (eg the same for all observers) of something called the "energy-momentum 4-vector." That is, there is a relationship between energy and momentum:

sqrt(E^2-P^2c^2)=mc^2

which is fundamentally different from the Newtonian

E=(P^2)/2m.

This difference ultimately comes from the difference between the geometry of spacetime itself in the Newtonian and relativistic descriptions.

Answer 5

Whoa. Mass changes with change of speed of an object? Where'd you get that?
E=mc^2 only states the amount of energy in any mass. Speed is constant here (speed of light).
Ke = (mv^2)/2 this is kinetic energy, and true, if you hold energy constant, you can change the values of mass and velocity, but that would not mean you're making your object lighter or faster, it would mean you're using a different object :).

Answer 6

In normal conditions, mass does not change with speed...ya weight of the body does chang e and this is because of variation in gravitational force on us..possibly due to altitute,latitude or the speed of earth's rotation .
E=mc^2 simply denotes that E is the energy liberated when mass m is lost in case of mass energy conversations like nuclear fission or fusion...c is always a constant in vaccum
In case of moving with velocity close to the speed of light..3 * 10^8 m/s ...than according to the relatavity theory mass varie sby a factor "gamma" which is
M=m/(1-v^2/c^2)
and is practically impossible

Answer 7

Mass of an object increases with speed as per theory of relativity.

This increase in mass is significant only when an object is moving with a speed comparable to the speed of light.

For all practical purpose since the speed of an object is very much less than the speed of light we can ignore the increase in mass of an object due to its speed.

Answer 8

Because of the equation: E=mc^2, and with a complicated calculations, we get the next:

mr = m0 /sqrt(1 - v^2/c^2)

where v is the vilocity of the body.
c is the speed of light.
m0 the initial mass(with no movement).
mr the motion-based mass.

so that with a very big velocity the mass will change.

Answer 9

You got it. As you add energy, something has to change on the other side of the equation. As c is a constant, that leaves only mass. So that's what increases.

Answer 10

Mass should not change as speed change.

The energy of the mass changes as the kinetic energy changes.

Keep in mind that speed is a relative. At different reference point, the energy level is different, but the mass will always stays the same.

The only areas that I think mass will change is nuclear reaction or inside the black hole where mass becomes energy.