davecoulter
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 Jun 13 awarded Critic Jun 13 comment Why do metal objects in microwaves spark? Well, we can think of the electric field as induced by the changing magnetic field, but similarly the changing electric field induces a magnetic field. This goes back and forth with light and so conventionally we think that the emf in a conductor is caused by a magnetic field in flux. But yes, it is the induced electric field that provides the force. Jun 13 answered Why do metal objects in microwaves spark? Mar 28 comment About the work done by gravity to pull the object down to the earth surface user1285419 - it is still conservative because the total energy of the system (i.e. the space-craft/Earth system) never changes. This of course assumes an ideal system with no friction. The expression of $GMm/r^2$ just happens to be the expression that describes how the force of gravity changes in our observed universe... it is an experimental fact. In another universe that expression might be different, but in that other universe if the force was conservative, then regardless of the mathematical expression of the force, the total energy of the system (potential + kinetic) would be constant. Feb 28 comment Intuitively Understanding Work and Energy +1 - I like this statement of fact, because well, it is the way it is. Scientific laws are codified observations, and as such are as close to truths as we can get. Theories and mathematical tools can be used to explain and describe various fundamental phenomena, but if the Universe was different then we'd have different theories and maths... The observed will always, and should always, trump our expectations, assumptions, need for symmetry, or our anthropocentric need to understand "why." Feb 24 answered Ohmic and Non-Ohmic devices Feb 24 awarded Teacher Feb 24 answered Is 'restoring force' a particular type of force? Aug 3 comment Hubble time, the age of the Universe and expansion rate Thanks-- I've been randomly thinking about the meaning of the Hubble Time and although I could readily understand that it is the reciprocal of Hubble's Constant, I didn't see why this should be synonymous with the age of the Universe. In thinking about your explanation I still don't have a deep physical intuition about it (I am not sure why I am slightly embarrassed by that), although I am satisfied with the more abstract mathematical explanation. Aug 3 awarded Autobiographer Aug 3 awarded Supporter