Physics Asked by user7519 on April 15, 2021
Is energy dissipated by friction the same as work done by friction where the equation is W(friction) = Ff * d cos theta .
However, since work is the transfer of energy and not energy itself then is it valid to state W(friction) is energy dissipated by friction?
Sometimes, but not always.
Consider two tires on fixed axles, positioned so that their treads touch. When you spin one tire, the other one also spins. The reason the other tire gains energy is because the friction between one tire and the other does work on it. In this case, the work done on the second tire by friction is equal to the sum of the rotational kinetic energy of the second tire and the energy dissipated as heat and sound.
Another common example: when you rub a balloon on your hair, friction causes both the balloon and your hair to become charged. There is an energy associated with creating this charge distribution; therefore, the work done by friction is equal to the sum of the energy of the charge distribution and the energy dissipated as heat and sound.
Correct answer by probably_someone on April 15, 2021
The answer is not simple. The work done by friction on the center of mass (CM) of the sliding object is different from the work done on the sliding object based on the first law of thermodynamics. The problem is that the term "work" is used to denote two different concepts. Elementary physics treatments consider work based on the CM using Newton's laws of motion and that is the treatment used in the prior answers; this is correct but it provides no information on "heating up of the object". The object does have an increase in internal energy and that cannot be calculated using the laws of motion; the first law of thermodynamics must be used. See "Work and Heat Transfer in the Presence of Friction", Sherwood and Bernard, Am. J. Physics 52(11), Nov 1984. They denote the work on the CM as pseudo-work and use work to denote work in the first law.
Answered by John Darby on April 15, 2021
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