1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

? about light

  1. Mar 18, 2009 #1
    if we had a scale with a mirror on top then we zeroed the scale and the scale was on earth well in our case we need a stronger gravitational
    field and a light beam comes by the scale and then enters the strong gravitational field
    thus the light is bent into the scale and hits the mirror and bounces off would the scale register a weight? all-be it a small one. or if we had a space-craft in outter space with mirrors on it and we shined a huge laser at it would the space-craft move , for every action there is an equal but opposite reaction.
  2. jcsd
  3. Mar 18, 2009 #2


    Staff: Mentor

    Yes. Light has momentum.
  4. Mar 18, 2009 #3
    does this imply that light has mass, cause if the scale registers weight
    w=mg i know p=E/c for a photon
  5. Mar 18, 2009 #4
    Light (a whole bunch of photons) exerts a pressure on the scale's surface. See link: http://en.wikipedia.org/wiki/Radiation_pressure.

    Weight is a force, w = mg. Pressure (radiation pressure in this case) times area is a force too, F = pA.
  6. Mar 18, 2009 #5
    i see that makes sense now .
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: ? about light
  1. About light (Replies: 6)

  2. About light (Replies: 3)

  3. About light (Replies: 1)