5 ms·

That's silly. My flashlight shoots stuff at speed of light all the time. Mass matters. Shooting just enough mass at very high velocity is not much different th

That's silly. My flashlight shoots stuff at speed of light all the time. Mass matters. Shooting just enough mass at very high velocity is not much different than shooting a lot more mass at lower velocity, in terms of force.

LoganDark 3y ago
> Mass matters. Exactly. You try accelerating 200kg up to anywhere close to the speed of light (say 80%). That is a lot of force. Technically even photons can exert force on objects, but they have such a small mass that it's a difficult effect to observe.
- hotpotamus 3y ago
  From memory, photons are massless, otherwise they could not move at light speed. They do have momentum though.
  - LoganDark 3y ago
    Oh, thanks for the correction.
  - eru 3y ago
    Photons have mass, but no rest mass. (Or something like that.)
    - scubbo 3y ago
      Momentum but no mass, if I recall my physics correctly (low certainty). Wait, hang on, we have access to an appreciable-chunk of the world's knowledge at our fingertips... https://en.wikipedia.org/wiki/Photon https://en.wikipedia.org/wiki/Photon - "Photons are massless[...]In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p[...]Current commonly accepted physical theories imply or assume the photon to be strictly massless"
    - tsimionescu 3y ago
      Typically momentum is thought as mass times velocity, and since photons do have momentum, there was a desire to give them some kind of "relativistic mass". In more recent times, it has been seen as easier to use just one concept of mass, and to redefine momentum entirely. So, photons have a mass of 0, and we don't need to specify "rest mass". But they do have momentum.
- jvanderbot 3y ago
  This is getting overly pedantic. Opening comment said that you'd need absurd amounts of mass to accelerate a person to near light speed. I said that the velocity of ejecting that mass mattered. That if you could push out mass at speed of light, you'd need a lot less mass. Not that you'd push out the same mass at speed of light. Or that you could arbitrarily push things out at speed of light. Sheesh.

LoganDark 3y ago

> Mass matters. Exactly. You try accelerating 200kg up to anywhere close to the speed of light (say 80%). That is a lot of force. Technically even photons can exert force on objects, but they have such a small mass that it's a difficult effect to observe.

hotpotamus 3y ago
From memory, photons are massless, otherwise they could not move at light speed. They do have momentum though.
- LoganDark 3y ago
  Oh, thanks for the correction.
- eru 3y ago
  Photons have mass, but no rest mass. (Or something like that.)
  - scubbo 3y ago
    Momentum but no mass, if I recall my physics correctly (low certainty). Wait, hang on, we have access to an appreciable-chunk of the world's knowledge at our fingertips... https://en.wikipedia.org/wiki/Photon https://en.wikipedia.org/wiki/Photon - "Photons are massless[...]In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p[...]Current commonly accepted physical theories imply or assume the photon to be strictly massless"
  - tsimionescu 3y ago
    Typically momentum is thought as mass times velocity, and since photons do have momentum, there was a desire to give them some kind of "relativistic mass". In more recent times, it has been seen as easier to use just one concept of mass, and to redefine momentum entirely. So, photons have a mass of 0, and we don't need to specify "rest mass". But they do have momentum.
jvanderbot 3y ago
This is getting overly pedantic. Opening comment said that you'd need absurd amounts of mass to accelerate a person to near light speed. I said that the velocity of ejecting that mass mattered. That if you could push out mass at speed of light, you'd need a lot less mass. Not that you'd push out the same mass at speed of light. Or that you could arbitrarily push things out at speed of light. Sheesh.