A lever is a rigid bar that can turn around a pivot point, called a
fulcrum. A lever is a simple machine and can be moved to move a load
(or do work). Effort is applied to one part of the lever and it pushes
the load at another part. Using a lever makes it easier to move a load
and so you use less effort.
There are three kinds of levers:
1) First Class Lever -- the effort and the load on either side of
the fulcrum. Some examples would be a crowbar or a seesaw. The effort
is only less than the load if the load is closer to the fulcrum. The
lever then acts as a force magnifier and the mechanical advantage is
greater than one. If the effort is closer to the fulcrum, then the
effort is larger than the load and the mechanical advantage is less
than one. In this case the lever acts as a movement magnifier.
2) Second Class Lever -- the load is between the fulcrum and the
effort. An example is a nutcracker or a wheelbarrow. This type of lever
always acts as a force magnifier and its mechanical advantage is
greater than one.
3) Third Class Lever -- the effort is between the load and the
fulcrum. An example is a pair of sugar tongs. This is a movement
magnifier which means its mechanical advantage is less than one. The
load moves more than the effort. (When you use sugar tongs, a small
movement of the fingertips makes the jaws of the tongs move a lot.)
(republished on 07/13/06)