Speed light and mass?

Question

So it is said that an object moving at the speed of light gain infinite mass. So if light is moving at the speed of light shouldn't it have infinite mass? So if it has a velocity of light and infinite mass, shouldn't it have infinite momentum? So if it has infinite momentum shouldn't it like if I point a flashlight to a wall the wall iw would like be a photon cannon?

I know my hypothese has a problem so can anyone tel lme?

Answer 1

Two important misconceptions:



First, objects approaching the speed of light do not...not...gain rest mass, m. That's why it's called "rest" mass; it's the mass we observe (in kg for example) when the object is at rest re us. Rest mass, BTW, is the mass in e = mc^2, which is the energy equivalent to that rest mass.



What objects gain is inertia, M = m/sqrt(1 -(v/c)^2), which means it takes more and more force F = Ma to keep objects accelerating even though the rest mass, m, has not changed. And that's why objects with rest mass cannot reach, let alone exceed, light speed, there is not enough force in the whole universe to keep the objects accelerating as their relativistic inertias (M) approach infinity.



Second, photons are rest mass less. So M = m/sqrt(1 -(v/c)^2) does not apply to photons and any other rest massless particles. But they do have momentum, which has been measured in the labs and is used, for example, in laser applications. And that momentum is expressed by E = Mc^2 = Pc = hf so that P = hf/c is the momentum of photons with energy E = hf and frequency f. Note M is in fact the relativistic inertia cited above.



Also note that this photonic momentum comes strictly from the energy of the photons. There is no rest mass involved. In fact, we can show [See source.] that when anything travels at v = c, light speed, it cannot have rest mass. That is, when v = c, m must = 0.



Also note, P = hf/c is per photon. h is Planck's Constant, a very very small number that drives P to be small as well. And dividing by c, which is a very very large number, makes P even smaller. So to check out your flashlight assertion, which is incorrect, look up and plug in some visible light frequency (say green), plug in h = 6.63E-34 J.s, and divide the whole thing by c ~ 3E8 m/s. You will see the momentum of a single green photon is very very very tiny indeed.



A 60 Watt bulb will burn your hand at a distance of about 1/2 inch or so. That's 60 J/s = E/T = NPc/T where N is the number of photons and T is the interval over which N is pumped out; so for your flashlight to burn someone's hand, you'll need N/T = 60 /Pc = 60/hf photons per second pouring out of that flashlight. And that's on the order of 10^34 photons/second. As intensity can be measured in photons/second, I think you can see your puny little, 1 Watt flashlight will hardly be pumping out that many photons per second. And that's a good thing, as you wouldn't want to burn your friend's face when you shine the torch into his eyes.

Answer 2

There are "element" that could commute a the cost of sunshine: mild and gravity you're good, mild can't be interpreted as some thing that has no mass. yet what's it then. Einstein admired equation "E=mc^2" let us know that ability and mass are appropriate, diverse styles of the comparable element. Mass is, in accordance to Einstein is an exceedingly super concentration of ability that is switched over to a greater "direct" variety of ability. once you commute to speeds close to the cost of sunshine, your mass starts off starting to be mild, the main direct variety of ability (returned, in accordance to Einstein), and once you eventually commute on the cost of sunshine, all your mass will become mild and there is not any coming decrease back, mild can't cut back velocity. because of the fact of this mild velocity is the "primary" velocity shrink, because of the fact mild is the main direct source of ability and travels at that velocity!!!!! :O

Answer 3

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Answer 4

1) apparent mass: the Lorentz transformation tells you that the apparent mass of an object goes like

m0 / sqrt( 1 - (v/c)^2);

where m0 is the "rest mass" of the object,

c is the speed of light

and v is the velocity at which the object is travelling.



That's the piece of special relativity where the notion "a massive object moving at speeds approaching the speed of light seems to have mass approaching infinity" comes from.



2) light is made up of photons, and photon have zero mass. m0 = 0.



3) light has no mass, but it does have momentum. But this momentum is not a p=mv (classical) momentum -- turns out it works out the other way around: physicists work with mass and momentum (m,p) then show that in the limit of classical mechanics (low velocities compared to the speed of light) that momentum degenerates to p=mv, allowing you work with mass and velocity (m,v) in the classical limit. Note: the fact that light has momentum and zero mass is used in developing the theoretical basis for the "solar sail" concepts -- where the momentum of light from the sun is used to push a solar sail, propelling a space craft away from the source of the sunlight.



4) When you point a flashlight at a wall, it does act like a photon cannon -- because that is what it is: a source of light particles delivering their momentum to the wall. However, the momentum of light is not infinite, and how well the wall handles the momentum of the photons should give you a good idea of how much momentum the light particles from the flashlight photon cannon has. [NB: this is not entirely facetious -- a high energy laser that can deliver gigawatts on a picosecond time scalle is using the momentum of those photons to carve out picometer scale holes in even the hardest of metals.]

Answer 5

speed of light is 3*10^8 approx..according to Einstein's theory the mass of an object is decreased if it goes with a velocity.it can be understood by an equation

M=Mo/sqroot(1-v^2/c^2)

Mo=intial mass of an object

M=mass of an object after going with velocity 'v'

c=speed of light

so an object mass would be changed if it moves

if an object(photon) moves with speed of light we can find from the above equation thar M=infinite

so no object can move with speed of light

M= infinity is in the sense that the object moving with speed of light has no mass.

therefore,mass of photon is zero.

Answer 6

well its actually the speed of the electromagnetic spectrum because all waves in the electromagnetic spectrum travel at the speed of light. these are the only things actually able to travel at the speed of light. This question can't really be answered fully because no one really understands or knows exactly what light is. the theories work but we think of light as waves and as photons in different circumstances.



light has no mass anyway so if you multiplied it by infinity you would get zero. therefore it cant have momentum because it has no mass!



this is the best i can explain it!

Answer 7

Remember, light has no mass. Only (in theoretical terms) it can have gravity when sucked into a black hole. But, since it has no mass, which is 0, 0 times infinite or anything is 0. So it wont be like a photon cannon.





If this is wrong, plz don't thumbs it down.