MadSci Network: Physics
Query:

Re: Does the following situation violate conservation of energy?

Date: Mon Dec 6 20:47:28 2004
Posted By: Jerrold Franklin, Professor Emeritus
Area of science: Physics
ID: 1101779924.Ph
Message:

You have to be careful in using the EM field momentum vector for static 
fields.  In order for the field momentum to exert an impulse on any 
object, there must be a traveling wave that reflects from (or is absorbed 
by) the object.  In the calculation for sunlight moving a solar sail, it 
is the reflection of the traveling wave that produces the impulse.  This 
can also be calculated using the force on currents in the sail induced by 
the oscillating fields of the wave.  If the wave isn't moving or 
oscillating in time, there will be no force. 


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