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!

Radiation Pressure and KE

  1. May 20, 2008 #1

    When radiation pressure exerts a force on an object causing it to move, where does the object's kinetic energy come from, and how?

    E.g. consider a perfectly reflecting solid block in vacuum. Its face is illuminated by light. From conservation of momentum, the reflection of the light from the block's surface causes the radiation force, which accelerates the block.

    The block has gained KE, but it can't be absorbing the photons, since it is perfectly reflective. Does this mean that the reflected photons are actually lower energy than the incident photons? But how:confused:? Some kind of Doppler shifting going on?

    Any help is much appreciated!
  2. jcsd
  3. May 20, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Exactly. The reflected photons are red-shifted by the movement of the block.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Radiation Pressure and KE
  1. Radiation pressure (Replies: 1)

  2. Radiation pressure (Replies: 1)