Ages ago in my physics classes my teacher would have a large metal motor that would spin very fast, it was attached to a metal board. When he asked people to hold it it felt really stange and would pull you in apparently random directions. When it didnt spin it was very heavy but when it was spinning it's weight felt as though it changed, but I can't imagine it weighing less on scales. He would always say that he wanted to know what the force was, does anybody know about it or have any links? (sorry if this was a nooby question) Thanks, Tom.