Hi Arthur -
A first class lever has the fulcrum betwen the ends, with load at one end and effort at the other end. (Think of a see-saw). In this case the force closest to the fulcrum is greater, but moves a shorter distance. So these can either provide speed-up or mechanical advantage, depending on which end is which.
A second class lever has the fulcrum at an end, effort on the other end, and load in the middle. (Think of a wheelbarrow). Second class levers always provide a mechanical advantage. The effort is always less than the load, and always moves farther than the load.
Actually, if you look at the lug wrench in detail, the point that doesn't move (the fulcrum) is in between different parts of the load- the different sides of the nut. So you could think of the wrench as a mixture of those two classes of lever. Either way, your hand moves a lot more than the lug nut does. If the wrench didn't give you a mechanical advantage, there wouldnt be much of a point in using it, would there? :)
Just for good measure, I figured I'd mention third class levers too. Third class levers have the fulcrum at one end and the load at the other end, with the effort being in the middle. Third class levers do NOT give a mechanical advantage, but extra speed results in place of power. The effort is always greater than the load, but the load moves farther than the effort force. A baseball bat is a good example of a third class lever.
I hope this helps!
~Bob (w. Mike)
(republished on 07/13/06)