Re: questions about light

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#1573

From: Edward Van Nostrand
Date: Wed, 27 Apr 1994 11:04

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Just a comment about your answer to 2. below


> >2. If light is a particle, when it leaves a flashlight why doesn't it
> >have enough momentum to push the flashlight backward?
>
> No mass, no momentum, no recoil.
>
Though light doesn't have mass it still has momentum.  This is  the
principal behind the light sail for spacecraft.  The momentum is given by

p=h x frequency /c where h = Planck's constant and c is the speed of light.

If the flashlight were not affected by forces such as gravity and friction
at its location it would indeed move backwards under the influence of the
weak force exerted by the photons.

Ted van Nostrand
Holy Heart High School
St. John's, NF, Canada

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From: Edward Van Nostrand <evannost@CALVIN.STEMNET.NF.CA>
Subject: Re: questions about light
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