![]() It depends on the velocities of the two bodies at the contact point(contact plane). So, isn't it incorrect to say that work done on the system is the negative of the work done by the system? ![]() ![]() I have just taken the first law of thermodynamics as an example. My question is not really related to thermodynamics, but something more fundamental. Kindly note that I am already aware of the different conventions used in physics and chemistry, and I completely understand their intended meanings. But, if the work done by a system is not equal to the negative of the work done on it, then I have a feeling that the chemistry definition might be a better one. The first law of thermodynamics in the physics point of view is: $\Delta U=Q-W,$Īnd in the chemistry perspective is: $\Delta U=Q+W.$īoth of these seem to be correct, as in the first case we are considering the work done by the system on the surroundings, and in the second case we are considering the work done on the system by external forces. If the work done by a system is not always the negative of the work done by the system, then how can both versions of the first law of thermodynamics hold true? On the other hand, the block performs no work on the table, since the table surface does not get displaced at all. Due to friction, the table performs work on the block, thereby reducing its kinetic energy. I consider my system to include only the block. We have already given it an initial velocity.
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