What examples show that interactions change the speeds of both bodies?

Consider the first example: a man mooring on a boat to the shore pushes off the bow of the boat and jumps onto the shore through the water. From this jolt of speed, both the man and the boat changed. The man jumped – his speed increased, pushed off the boat – the boat changed speed, moving away from the shore. Second example: two people in two different boats are slowly approaching each other, and one of them pulls the other’s boat to his boat. The interaction again changes the speeds of both bodies.