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# Re: are normal reaction and tension conservative ?

Chetan wrote:

are normal reaction and tension conservative ?

Chetan-

I like what John Mallinckrodt wrote to you, but I would like to add a
bit to it.

Really, there is no such thing as a "non-conservative" force. As far as
we know, all four fources in nature (gravity, electromagnetism, strong,
and weak) are completely conservative.

Additional forces that we consider in mechanics courses like the normal,
friction, and tension, are convenient ways of describing complicated
interactions as though they were simple things. For example, when we
pull on a rope, we are stretching all the bonds between the molecules
that make up the rope. All these bonds are like very small, but very
stiff springs. If we stretch them, they pull back. That is the origin
of the force we call "tension." Of course, it is terribly inconvenient
to try and describe the effect of a rope in terms of 10^23 or so
springs, but it turns out that we can make a pretty good approximation
by treating it as this single force we call tension.

Now, how do we decide whether a force is conservative or not? First,
does the force do any work in the situation you are considering? If no
work is done, then it is meaningless to ask whether the force is
conservative. (Consider a block at rest on an inclined plane: the
force that holds it in place is the "non-conservative" force friction,
but no energy is being lost in this situation.)

If the force IS doing work, your second question is "where is the energy
going, and can I get it back?" Work is process by which energy is
transformed from one form or object to another. If the energy winds up
as potential (using a rope to lift a brick, for example), then it can be
"recovered" (as work done on the brick by gravity as it falls) and we
can call the force that did the work (the tension in the rope)
"conservative." If the energy goes into making things hot, as with
sliding friction, then we call it "non-conservative." That energy
cannot, generally speaking, be used to do work on anything.