Levers
Lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum.
http://eschooltoday.com/science/simple-machines/what-is-a-lever.html
Lever Arm- - The lever arm is defined as the perpendicular distance from the axis of rotation to the line of action of the force.
Mechanical Advantage = Effort Arm / Load Arm
Classes of Levers:
Class 1: Fulcrum is directly in the middle, the effort is applied on one side of the fulcrum and the resistance (or load) on the other side, for example, a seesaw, a crowbar or a pair of scissors.
http://www.school-for-champions.com/machines/levers.htm#.Wh7f9ceGPIU
Class 2: Resistance (or load) in the middle: the effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow, a nutcracker, a bottle opener or the brake pedal of a car. Mechanical advantage is always greater than 1.
Class 3: Effort in the middle: the resistance (or load) is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the human mandible. Mechanical advantage is always less than 1.
Examples
