Leverage is a vital concept for mechanics – and everybody uses leverage on a daily basis to make everyday tasks possible and to make difficult tasks easier. A lever has three essential parts.
The fulcrum of a lever is the point at which it can swivel: the balancing point of a see-saw, the wheel of a wheelbarrow, the back legs of a chair as someone leans back precariously on it, the edge of a desk on which someone has balanced a ruler – these all form a fulcrum that will allow the lever to move.
The load is the weight being moved: the dirt in a shovel, the ammunition in a trebuchet, the child on a see-saw, the peas in a spoon.
The effort is the force that will move the load: a person's bicep about to lift the groceries, the other kid about to jump on the see-saw, the adult's torso teetering back in the chair, the hand squeezing the nutcracker.
The fulcrum, effort, and load can be arranged in three different ways, each of which works slightly differently to make up the lever.
First-Class Levers
A first-class lever has a load, then a fulcrum, and then an effort.
A first-class lever is usually a classic and easily-recognisable form of leverage.
A see-saw is a clear example of a first-class lever. Two first-class levers working together are a pair of scissors.
Second-Class Levers
A second-class lever has a fulcrum, then a load, and then an effort.
A wheelbarrow is a second-class lever, and so is a chef's knife balanced on its tip as the chef chops up a carrot.
Third-Class Levers
A third-class lever has a fulcrum, then an effort, and then a load.
Unlike some first- and all second-class levers, a third-class lever requires more effort than load. It's still useful because of its ability to move the load a long distance relative to the effort.
A pair of tongs is a pair of third-class levers. A hammer, when wielded, is a third-class lever.
Mechanical Advantage
Levers allow us to move heavy loads with a small force, or move loads a long way with only a small movement of effort. These benefits are called a mechanical advantage.
For example, when a person stands and rises onto her toes, she is using her ankle joint as a third-class lever. Ballet dancers, however, continue to rise as high as possible onto their toes, for a very good reason: if they are flexible enough to bring their ankles in front of their toes, they have converted the ankle joint into a much more mechanically advantageous first-class lever.
For further information, see The Lever – Finding the Mechanical Advantage and Classes of Levers.
Elisabeth Marshall - Elisabeth Marshall is a certified Pilates instructor with an interest in anatomy and biomechanics, imagery, and bodywork. She taught ...
Join the Conversation