Sand is made of tiny pieces of rock that have been worn down by wind and water. explain why the formation of sand is a physical change.

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

The solid that is formed and usually sinks to the bottom of a solution is the

Positive ions differ from neutral atoms in that