Friction, heat, and floating

Friction is the drag between two faces that are trying to slide. A rougher face or more weight means more drag. Oil, rollers, or a smoother face means less. If the part does not move, friction is holding it and the work done on that part is zero.

Heat moves from the hotter thing to the cooler thing. A hot bearing warms the bench. It does not pull cold out of the bench. Heating metal makes it grow a little, which is why a tight pin can seize, and why warming a hole can let the pin in.

Density is weight for the size. The two blocks in the drawing are the same size, so the heavier one is denser. A solid chunk denser than water sinks. A hollow hull can float because the air inside makes the average density of the whole hull less than water. Underwater, a scale reads light by the weight of the water pushed aside. That upward push is buoyancy.