Here is what I know:
Photons have no mass.
Force is change in momentum over change in time.
Momentum is mass times velocity.
E=mc²
SO HOW DOES LIGHT HAVE ENERGY AAAA
I also read that massless particles can have momentum and I do not understand that at all.
Please explain how all of this is connected and how light has energy and exerts force. Thank you!
In: 9
Photons are unique.
Even though photons have no mass, they still have momentum proportional to their energy, given by the formula p=E/c. Because photons have no mass, all of the momentum of a photon actually comes from its energy and frequency as described by the Planck-Einstein relation E=hf, and NOT E=MC squared.
Photons have relativistic mass, so it satisfies E=mc^2. All of that mass is attributed to the kinetic energy. What you are looking for is rest mass, if a particle didn’t move. And it’s correct that a photon would have in fact, no mass at standstill.
Since this is ELI5, not askscience, here we go.
Newtonian physics is great. Until you get into particle physics. Then it starts to fall apart. That’s where special relativity comes into play.
You need to stop thinking of mass as something other than another form of energy. Thinking about it, being able to convert between energy and mass makes sense, right? Well, of they were fundamentally different, it wouldn’t make sense to be able to convert between the two. So instead of thinking about momentum being strictly mass, think of it as energy. Photons don’t have mass because all of their energy is in the form of motion. Therefore, their momentum is derived from their energy, not their mass.
The full formula is E^2 = m^2 c^4 + p^2 c^2
E=mc^2 is a simplification for particles with mass at rest.
Photons carry momentum (p) and thus have energy.
Note that force is change in momentum over time, but it doesn’t really apply to individual photons.
A single photon transfers it’s momentum instantaneously. Though if you have a steady stream of photons you can calculate a force based on the average rate of momentum transfer.
Yes it’s weird.
You’re referencing simple Newtonian equations and trying to apply them to light, but light is an inherently relativistic phenomenon. They just don’t go together.
Are you currently studying physics? If you are, it’s really important to keep track of what assumptions you make while deriving a particular equation, otherwise you may apply equations incorrectly. Not to mention, things will make a lot more sense in general.
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