If light has energy but no mass, how can it have momentum?
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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).
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).
Photons have zero ‘rest mass’, however photons only exist moving at the speed c. So if they’re never not moving, ‘rest mass’ is really just theoretical.
Photons have zero ‘rest mass’, however photons only exist moving at the speed c. So if they’re never not moving, ‘rest mass’ is really just theoretical.
Photons have zero ‘rest mass’, however photons only exist moving at the speed c. So if they’re never not moving, ‘rest mass’ is really just theoretical.
Some great explanations here, but most are way more complex than I could explain to my 5-year-old. How about this:
Photons (light) are often described as having the properties of both particles and waves. For the momentum piece, let’s focus on waves. **Picture a wave in the ocean:** It travels across the ocean with an observable momentum, however the drops of water do not travel with it. The photon of light travels across the electromagnetic field similarly to how the ocean wave travels across the surface of the water.
Some great explanations here, but most are way more complex than I could explain to my 5-year-old. How about this:
Photons (light) are often described as having the properties of both particles and waves. For the momentum piece, let’s focus on waves. **Picture a wave in the ocean:** It travels across the ocean with an observable momentum, however the drops of water do not travel with it. The photon of light travels across the electromagnetic field similarly to how the ocean wave travels across the surface of the water.
Some great explanations here, but most are way more complex than I could explain to my 5-year-old. How about this:
Photons (light) are often described as having the properties of both particles and waves. For the momentum piece, let’s focus on waves. **Picture a wave in the ocean:** It travels across the ocean with an observable momentum, however the drops of water do not travel with it. The photon of light travels across the electromagnetic field similarly to how the ocean wave travels across the surface of the water.
Easiest way I can explain it is that even though it has no mass, it still is a particle. Like throwing a balloon at someone still has impact. Balloons are relatively weightless but something it hits will react.
That means your shadow, has negative weight. And satellites in space, are impacted by the sun’s rays of lights pushing it.
Easiest way I can explain it is that even though it has no mass, it still is a particle. Like throwing a balloon at someone still has impact. Balloons are relatively weightless but something it hits will react.
That means your shadow, has negative weight. And satellites in space, are impacted by the sun’s rays of lights pushing it.
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