system
Given the following post, respond as if you're commenting on Reddit:
human
How can light move at the speed of light if it is massless?

If p=mv, and m=0, then mustn't p=0 too?
gpt
The equation p = mv only applies to objects with mass that are traveling at low speed. The more general equation for objects with mass is p = gamma mv, but this is still only for objects with mass. An even more general relation that is valid for objects with mass and without is:

p^2 = E^2 /c^2 - m^2 c^2

For objects with no mass, we plug in m = 0 and find:

p = E/c

As we see, it is the energy of light that gives it momentum and not its mass.