What is a lever?
- A lever is one type of simple machine that allows
energy to be used in the most advantageous way. Levers
can change the 1) direction of the applied force, 2) distance and speed
of movement produced by an applied force, 3) effective strength of the
- A lever is a rigid bar with three parts: the fixed
point around which the bar pivots is the fulcrum; the effort arm (in-lever
arm) is the part of the lever to which force is applied; the resistance
arm (out-lever arm) is the part that bears the load to be moved.
- The effort, or in-force, is applied to the effort
arm (in-lever); it is the force put into the machine to move the load.
- The out-force is the force the lever uses to move
the load, AFTER the effort force has overcome the resistance of the load
(weight). The resistance arm (out-lever) bears the load, so the out-force
is produced on this end of the lever to move the load.
- The effort applied to the lever (in-force)
must overcome the resistance that the load exerts on the lever (the weight
of the load or the force of gravity), in order to produce movement of the
- Mechanical advantage (MA) is simply the ratio of
the resistance force to the effort force (MA=Force of resistance/force
of effort). *Note: force of resistance is NOT the out-force. To increase
the MA, move the fulcrum closer to the load so that you shorten the resistance
arm and lengthen the effort arm; this allows you to put the same or less
force into the system to move more resistance. By lengthening the effort
arm, you are reducing the ratio of the resistance arm to the effort arm
(Velocity Ratio), and increasing the ratio of the resistance force to the
effort force. The higher the MA, the greater the power of the lever.
- Velocity ratio (VR) is the ratio of the lengths
of out-lever to in-lever (length of resistance arm/effort arm). To increase
the velocity ratio that the load is moved, increase the resistance arm by
moving the fulcrum closer to the effort. The higher the VR, the greater
the speed of the lever.
- There are 3 orders of levers that differ only in
the relative position of the fulcrum, effort arm, and resistance arm.