The definition of work done is F x d. Can I say that any gain or loss of energy must be due work being done?

Question

F=force, d=distance moved in the same direction of the force.

Answer 1

It depends on what level you're describing the system on. If you're describing it on a subatomic level, then absolutely yes, every change in energy in the system is due to force being applied to some particle over some distance.

If, on the other hand, you are attempting a more macroscopic description of things, then the answer is no, because while, say, heating a glass of water in a microwave will certainly add energy to the water, it doesn't exert a net force on the water as a whole, or cause it to go anywhere, and thus would not ordinarily be called work in the macroscopic sense (although, again, on the microscopic level you could appeal to the tug of the shifting electromagnetic field on water molecules as work).

As a side note, don't heat a glass of water in a microwave.

Answer 2

I f F is the force and d is the distance through which the force moves, then the work done by this force is always equals the energy that it has spent. It is given by F x d.

This is the mechanical energy spent by the force.

How this energy is transformed is a different question.

Suppose a force of 10 newton acts on on a mass of 10 kg and keeps it uniform speed of 2m/s.

This statement is wrong because a force always causes acceleration but we have said that it is moving with uniform speed.

But in nature we have seen objects moving with uniform motion under action of constant force. This is because of friction, in this case that an equal and opposite force acts on the mass.

Now considering the force of !0 newton, if the mass of 10 kg has moved through a distance of 4 meter the work done by the force is 10 x 4 = 40 newton.

The work done by the frictional force is also 40 newton.

But the work done by the friction has been converted into other forms usually into heat energy.

Thus the work done by the force is always force x distance and how this work is shared by other bodies is a different question.

Answer 3

In a pure sense, yes. But in reality, nothing is 100% efficient and something gets lost due to heat or friction. But on the other hand, heat is sometimes desired, so it's not always a loss. There [in theory] is never a energy loss or gain...only energy conversion.

Answer 4

No, sometimes heat transfer is responsible for gain or loss of energy.

Answer 5

have you ever seen a person having luggage(kuli) on his head and waking . mathematically his work done is 0
w= f. dl sin theata now direction of force of gravity and displscement are perpendicular to each other therefore theata is90 putting in equation
W=f.dl sin90 and sin90=0
w=0 but his enegy is lossed to overcome friction and other obstacles.

Answer 6

no loss of energy,,just a change to heat energy do to friction

Answer 7

There is also energy associated with disorderliness (entropy).