As any other mechanism, the lever mechanism is used to do certain jobs in an easier way. It consists of a beam located on a fulcrum which works as a pivot for the rotational movement. Snap hooks and carabiners use this principle in order to make it quick and easy to lock and unlock the hook in a critical situation.
The main or general purpose of a lever is escalating a force with a little effort; however, this may be different according to the final objective and the type of lever used. There are three types of levers: class 1 (first-order lever), class 2 (second-order lever) and class 3 (third-order lever). Each type depends on the position of the load to be moved, the effort to be made and the fulcrum or pivoting element.
Types of levers
Class 1 or first-order lever: in this case, the fulcrum is located between the load to be moved and the effort. The load and the effort forces work in the same direction. This type of lever results in less effort to move the load, although the movement of the effort will cover more distance. Some examples of the use of this type of lever mechanism are scissors, a seesaw or a crowbar.
Class 2 or second-order lever: This type of mechanism locates the load between the effort to be made and the pivoting element. This time, the effort is applied in the opposite direction of the load force, and some advantages are that the effort is even smaller than the effort needed in a class 1 lever and the distance between the load and the effort can be reduced. Some common and simple machines using this type of lever mechanism are a nutcracker, a wheelbarrow and a bottle opener among others.
Class 3 or third-order lever: finally, this type of levers locates the effort between the fulcrum and the load, and is the one which has a different purpose. Instead of escalating the force, it magnifies the distance of the movement, but the effort needed is bigger than the load being moved. Some examples are fishing rods, tweezers, shovels, etc.
(photo source: wikipedia.org)