Levers What is a Lever A lever is

Levers

What is a Lever? ! 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 1. Resistance Force Arm: the perpendicular distance from the line of action of the resistance to the fulcrum. 2. Effort Force Arm: the perpendicular distance from the line of action of the effort force to the fulcrum. 3. Fulcrum: the axis which a lever may rotate around

Classes of Levers 1. First Class Lever 2. Second Class Lever 3. Third Class Lever

First Class Lever 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 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

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 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 Tweezers Shoveling

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 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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