4LeversA lever is a rigid rod that is free to rotate around a fixed pivot pointThe fixed point that a lever rotates around is a fulcrum.
5Different Classes of Levers There are three classes of leversThese are defined by the location of the fulcrum relative to the effort force and resistance forceIn a first class lever, the fulcrum is between the effort force and the resistance forceIn a second class lever, the resistance force is between the effort force and the fulcrumIn a third class lever, the effort force is between the resistance force and the fulcrum
7Force and Work in Levers A lever makes work easier by changing the amount of force exerted, the distance over which the force is exerted, or the direction of the force.The effort you exert on a lever is called the effort force.The distance you push down is the effort distance.The force that the lever exerts on an object is called the resistance force.The distance the lever pushes up on an object is the resistance distance.The relationship between work done on a lever and the work does on a object is the formula:EFFORT FORCE x EFFORT DISTANCE = RESISTANCE FORCE x RESISTANCE DISTANCE
8Mechanical Advantage in Levers A lever’s mechanical advantage is the number of times a lever increases a force exerted on it.The mechanical advantage of a lever is equal to the ratio of resistance for to the effort force:MECHANICAL ADVANTAGE= RESISTANCE FORCE/ EFFORT FORCE
9The Law of the LeverThe distance from the fulcrum to the effort force is called the effort armThe distance from the fulcrum to the resistance force is the resistance arm.The law of the lever states, that for a lever to be balanced, the effort force times the effort arm must be equal to the resistance force times the resistance arm.
10Joints as Machine Structures Many of the body’s movable joints are actually fulcrumsThe joints in the body act as pivot points for the bonesThe bones act as levers, and muscles provide the force.Your thigh, wrist, shoulder, knee, and elbow joint are all third class leversThe thigh and shoulder is an example of a ball and socket jointYour wrist joint is an example of sliding jointYour elbow and wrist joints are examples of hinge joints.
12Your Bones and Muscles as Lever Systems The most common types of levers in your body is the third class lever.But your body also has first and second class levers as wellThere is always a lever where the effort force is applied at the point where a muscle attaches to a boneThe bone serves as a the lever, and the resistance force is the force exerted by the boneThe force may be used for many things like chewing, running, or lifting many thingsExamples of different levers:A first class lever is your neckA second class lever is the call of your feetA third class lever is your elbow