A simple example of a lever is a bar, which is pivoted at some point called a fulcrum. A lever allows the user to overcome a large load over a small distance at one end by applying a small force at a greater distance from the other end.
Using the right kind of lever in the right way allows a user to move larger loads with smaller efforts. The effort required to move any load depends on the relative distance of each from the fulcrum. The ratio of load and effort is called Mechanical Advantage.
If the effort distance from the fulcrum is greater than the load distance, then the effort required will be less than the load being moved. This is known as a 'positive mechanical advantage'.
If the load distance is greater than the effort distance, then the effort required is greater than the load being moved. This is known as a 'negative mechanical advantage', which is sometimes referred to as a 'mechanical disadvantage'.
There are 3 basic types of lever.
1. Lever of the first order
In this type of lever, the fulcrum is in the middle between the load and the effort. An example of this type of lever is a crowbar. Another is the seesaw.
2. Lever of the second order
In this type of lever, the load is in the middle, between the effort and the fulcrum. An example of this type of lever is a wheelbarrow.
3. Lever of the third order
In this type of lever, the effort is in the middle, between the load and the fulcrum. An example of this type is the human arm, where the elbow is the fulcrum, and the biceps muscles are the effort, and the hand (and whatever it is holding) is the load.