When you use a spoon to prise a lid from a tin you are using a simple machine called a lever. In fact, levers are the basis of many tools in and around your house and work.

The way levers operate is by an effort applied at a point, which moves a load at another point through a balance point called the fulcrum. It is the relative positions of these three points - the effort, the load and the fulcrum - that distinguishes the type or class of lever. There are three classes of lever 1st, 2nd and 3rd class.

First class lever
First class levers have the fulcrum between the force and the load. In using a screwdriver to lift the lid from a paint tin you are moving the effort over a greater distance than the load. By having the fulcrum (the rim of the tin) close to the lid (the load) a larger force can be applied to the load to open the tin. By this means you are reducing the effort required, this is what first class levers do best. Other examples of first class levers are pliers, scissors, a crow bar, a claw hammer, a see-saw and a weighing balance.

In summary, in a first class lever the effort (force) moves over a large distance to move the load a smaller distance, and the fulcrum is between the effort (force) and the load. As the ratio of effort (force) arm length to load arm length increases the mechanical advantage of a first class lever increases.

Archimedes referred to a first class lever in his famous quote "Give me one firm spot on which to rest (a fulcrum) and I will move the Earth".

Second class lever
In second class levers the load is between the effort (force) and the fulcrum. A common example is a wheelbarrow where the effort moves a large distance to lift a heavy load, with the axle and wheel as the fulcrum.

In a second class lever the effort moves over a large distance to raise the load a small distance. As the ratio of effort (force) arm length to load arm length increases, the mechanical advantage of a second class lever increases. In a wheelbarrow, the closer the load is to the wheel, the greater the mechanical advantage. Nutcrackers are also an example of a second class lever.

Third class lever
With third class levers the effort is between the load and the fulcrum, for example in barbecue tongs. Other examples of third class levers are a broom, a fishing rod and a woomera.

In a third class lever the load moves further than the effort (force) and the mechanical advantage is low, which is why it's difficult to apply great force to the load. This can be an advantage by not squashing sausages on the barbecue!

When you lift a load using your forearm you are using a third class lever. Your biceps muscles are attached to the forearm just in front of the elbow. The load is on the hand, and the effort is between the fulcrum (elbow) and the load.