Unit 13: Levers Flashcards

Three Parts of a Lever

• Force point (F): where effort is applied; the muscle's insertion point.
• Resistance point (R): where resistance acts; perpendicular from the fulcrum.
• Fulcrum (A): the axis of motion; center of gravity in the body segment.

First Class Lever

• Axis point is in the middle, with force and resistance points at the edges.
• Example: Triceps muscle at the elbow, similar to a see-saw.

Second Class Lever

• Resistance point is in the middle; force and axis points are at the edges.
• Example: A wheelbarrow.

Third Class Lever

• Force is positioned in the middle; resistance and axis points are at the edges.
• Example: Bicep muscle functioning as a shovel.

Principle of Levers

• Fundamental equation: Force × Force arm = Resistance × Resistance arm.
• Torque is calculated as: force × force arm / resistance × resistance.

Mechanical Advantages of Levers

• Mechanical Advantage (MA) formula: MA = FA / RA.
• Indicates how efficiently a lever amplifies force.

Force Lever

• A mechanical advantage that favors force when the force arm is longer than the resistance arm.
• First class levers may be force levers; second class levers always are.

Speed Lever

• A mechanical advantage that favors speed when the resistance arm is longer than the force arm.
• First class levers can also be speed levers; third class levers always are.

Jackson Strength Evaluation System Procedure

• Involves strapping equipment on hand or wrist, using the equipment applied in muscle strength testing.

Classification of Levers in Tools

• Golf club: Third class lever; top hand is the axis, bottom hand applies force, bottom of the club is the resistance.
• Swinging door: Second class lever; hinges act as the axis, door is the resistance, handle provides force.
• Shovel: Functions as a third class lever, similar to a golf club.

Calculation of Force by Biceps Brachii

• Assessment of force needed to support a 95 N weight in hand when attached at a 90-degree angle 4.0 cm from elbow's center of rotation, considering forearm and hand weight of 35 N at 17 cm from elbow.

Mechanical Advantage of First Class Lever

• The mechanical advantage (MA) varies based on arm lengths.
• MA > 1 when force arm is longer than resistance arm; MA < 1 when vice versa; MA = 1 when both arms are equal.