What is a good example of contact force

How do you tell if someone actually cares about you? and just say they do?

If a simple machine reduces the strength of a force, what must be increased?

Arigid tank is divided into two equal parts by a partition. one part of the tank contains 3 kg of compressed liquid water at 400 kpa and 60°c while the other part is evacuated. the partition is now removed, and the water expands to fill the entire tank. determine the entropy change of water during this process, if the final pressure in the tank is 40 kpa. use steam tables.