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Q & A: Force of light

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Most recent answer: 11/29/2013
Q:
if light has no mass why is it capable of generating force? isn't mass required to generate force? if force equals mass times acceleration how can light have an impact on an object and be without mass?
- matt jackson (age 20)
westland mi usa
A:

Hello Matt,

Yes indeed, light can generate a force.  I remind you that the full relativistic formula for energy, mass, and momentum is E2 = m2c4 + p2 .  Although photons have no rest-mass, m, they do carry momentum p.  Now a force is generated by a transfer of momentum so a light beam incident and absorbed by an object will experience a force.  This can be easily verified in the lab with a laser beam.

Even from the classical point of view electromagnetic waves can cause a force.   For example the force on a charged particle is  F = q(E + V B) which implies that electromagnetic fields carry momentum.  If you view a photon as a classical wave it still carries momentum.

 

LeeH                   

 


(published on 11/29/2013)

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