If light has energy but no mass, how can it have momentum?
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“P=mv” is from Newtonian mechanics, which is known to be an incomplete model of reality, but which sticks around because it’s an excellent approximation for everyday purposes. The momentum of light is one of the cases where Newtonian mechanics fails and we need to upgrade to relativistic physics, in which the momentum of a massless particle is Planck’s constant ÷ the particle’s wavelength, or *p = h / λ*.
“P=mv” is from Newtonian mechanics, which is known to be an incomplete model of reality, but which sticks around because it’s an excellent approximation for everyday purposes. The momentum of light is one of the cases where Newtonian mechanics fails and we need to upgrade to relativistic physics, in which the momentum of a massless particle is Planck’s constant ÷ the particle’s wavelength, or *p = h / λ*.
“P=mv” is from Newtonian mechanics, which is known to be an incomplete model of reality, but which sticks around because it’s an excellent approximation for everyday purposes. The momentum of light is one of the cases where Newtonian mechanics fails and we need to upgrade to relativistic physics, in which the momentum of a massless particle is Planck’s constant ÷ the particle’s wavelength, or *p = h / λ*.
Because the common-use equation are not complete.
E=mc^2 is the Mass–energy equivalence valid in rest frames. For object in motion it is E^2 = p^2 c^2 + m^2 c^4
The momentum equation p= m v is one of Newtonian mechanics, m is the rest mass. If you include the relativistic effect that is important when speeds start to approach it is the speed of light m is the relativistic mass, that is the total energy of a body divided by the speed of light squared
At a speed that is common for objects with a mass on Earth the difference between rest mass and relativistic mass is so thin that we can simply ignore it.
For a massless particle, you can use the Mass–energy equivalence and derive that momentum p = E/c where e is the energy and c is the speed of light
https://en.wikipedia.org/wiki/Mass_in_special_relativity
Because the common-use equation are not complete.
E=mc^2 is the Mass–energy equivalence valid in rest frames. For object in motion it is E^2 = p^2 c^2 + m^2 c^4
The momentum equation p= m v is one of Newtonian mechanics, m is the rest mass. If you include the relativistic effect that is important when speeds start to approach it is the speed of light m is the relativistic mass, that is the total energy of a body divided by the speed of light squared
At a speed that is common for objects with a mass on Earth the difference between rest mass and relativistic mass is so thin that we can simply ignore it.
For a massless particle, you can use the Mass–energy equivalence and derive that momentum p = E/c where e is the energy and c is the speed of light
https://en.wikipedia.org/wiki/Mass_in_special_relativity
Because the common-use equation are not complete.
E=mc^2 is the Mass–energy equivalence valid in rest frames. For object in motion it is E^2 = p^2 c^2 + m^2 c^4
The momentum equation p= m v is one of Newtonian mechanics, m is the rest mass. If you include the relativistic effect that is important when speeds start to approach it is the speed of light m is the relativistic mass, that is the total energy of a body divided by the speed of light squared
At a speed that is common for objects with a mass on Earth the difference between rest mass and relativistic mass is so thin that we can simply ignore it.
For a massless particle, you can use the Mass–energy equivalence and derive that momentum p = E/c where e is the energy and c is the speed of light
https://en.wikipedia.org/wiki/Mass_in_special_relativity
Hello, physicians.
Appreciate the discussion you’re having with each other. However…
None of your explanations are Eli5. Please explain like some of us are absolute seagulls in terms of knowledge.
Much love,
I Don’t Intrinsically Onderstand Things
Hello, physicians.
Appreciate the discussion you’re having with each other. However…
None of your explanations are Eli5. Please explain like some of us are absolute seagulls in terms of knowledge.
Much love,
I Don’t Intrinsically Onderstand Things
Hello, physicians.
Appreciate the discussion you’re having with each other. However…
None of your explanations are Eli5. Please explain like some of us are absolute seagulls in terms of knowledge.
Much love,
I Don’t Intrinsically Onderstand Things
Mass has momentum, but so does energy. In a way, mass and energy are kind of the same thing, or you could think of them as two different forms of the same thing.
Most things we deal with have lots of mass and are moving very slowly, so their momentum is almost entirely determined by their mass and velocity. You might be familiar with the equation *momentum = mass × velocity*. This is a pretty close approximation for most everyday things.
Some things, like light, have little or no mass and are moving very quickly, so their momentum is almost entirely determined by their energy and velocity. The equation for the momentum of light is a little too complicated to type neatly in Reddit, but you can see it at Wikipedia’s article on [mass in special relativity](https://en.wikipedia.org/wiki/Mass_in_special_relativity).
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