Levers

What is a Lever?! In Our Body A lever is a rigid bar that rotates around an axis (fulcrum). In Our Body Bones  act as the rigid bar Joints  act as the axis (fulcrum) Muscle  apply the force

A Lever Consists of Three Components Resistance Force Arm: the perpendicular distance from the line of action of the resistance to the fulcrum. Effort Force Arm: the perpendicular distance from the line of action of the effort force to the fulcrum. Fulcrum: the axis which a lever may rotate around

Classes of Levers First Class Lever Second Class Lever Third Class Lever

First Class Lever Mechanical Examples The fulcrum is between the effort force & the resistance force. The effort force & the resistance can be at an equal distance from the fulcrum, or one may be farther away than the other Mechanical Examples Scissor teeter-totter

Anatomical Example Extension of the head Fulcrum: Atlanto-occipital joint Resistance: weight of the head Effort force: neck extensors

Second Class Lever Mechanical Examples The resistance is between the effort force & the fulcrum. The effort force & the resistance are on the same side of the axis, with the resistance closer to the fulcrum Mechanical Examples Wheel-barrow Nutcracker

Rising of heals to stand on toes Anatomical Example Rising of heals to stand on toes Fulcrum: metatarsophalangeal joints Resistance: weight of the body Effort force: Planterflexors (Calf muscles)

Third Class Lever Mechanical Examples The effort force is between the resistance & the fulcrum. The effort force acts between the fulcrum & the line of resistance force Mechanical Examples Fishing poles Shoveling Tweezers

Anatomical Example Forearm Flexion Fulcrum: Elbow joint Resistance: object held in hand Effort force: biceps muscle

What is Mechanical Advantage?! Mechanical advantage is the ratio of force arm to resistance arm of a giver lever. MA = effort force arm / resistance force arm

What If Mechanical Advantage = 1 Effort force arm = resistance force arm There will be a change in the direction of movement only

What If Mechanical Advantage > 1 Effort force is smaller than resistance force  distance effort force moves, meaning that the distance moved by the effort is greater than the distance moved by the resistance

What If Mechanical Advantage < 1 Effort force in more than resistance force  distance effort force moves, meaning that the distance moved by the effort is lesser than the distance moved by the resistance

In First Class Lever Mechanical advantage can be: = 1 < 1 > 1 Can be used to gain force advantage or distance/speed advantage

In Second Class Lever In Third Class Lever Mechanical advantage can be is ALWAYS > 1 Used to gain force advantage In Third Class Lever Mechanical advantage can be is ALWAYS < 1 Most human levers are class III

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