In the example on the previous page, we calculated that 450 n-m of work were done to move the rock.  You may wonder what a “n-m” is. We can express work by multiplying any unit of force times any unit of distance.  A "n-m" means that we multiplied newtons (unit of force) times meters (unit of distance). Usually, however, work is described in joules. The precise equivalent for a joule of work is when a force of 1 newton acts through a distance of 1 meter. A joule is the basic scientific unit for electrical, mechanical and thermal energy. In the above example, you and your friend did 450 joules of work.  So, 1 joule is the same as 1 n-m.  



1 Joule = 1 newton x 1 meter

What if you push against a huge rock and you can not even budge it? No work is done if the rock does not move, even though you use lots of energy and exert a lot of force in trying to move the rock. Work occurs only when a force succeeds in moving the object that the force acts on!

Interactive Question What mathematical equation would represent exerting 50 newtons of force on a rock and not being able to move it?