IB SEHS HL B.1.4 Levers

Lever

Simple machine made of a rod that rotates around a fixed point. Bones act as the rods in many biological levers.

A fulcrum is made of a

Rod, Fulcrum, Load force, Effort force

Fulcrum

A pivot point for the rod. In a biological lever, this is often a joint

Load force

The object that is being moved by the lever. In biological levers this an object held by the body, or body weight itself.

Effort force

The force required by the user of the lever to move the load. In a biological lever, this is done by one or several muscles

Force

A push or pull that causes an object to Strat or stop moving. This is often linear path.

Torque

Rotational force, or tendency to cause rotation about a fixed point

Torque Calculation

Multiply a force by the distance from the fulcrum that the force is applied

Mechanical advantage

Length of effort arm / Length of load arm = magnitude of load / magnitude of effort. If MA = 10, if you apply 5N of force, it will lift a 50N object.

Effort Arm

Length from fulcrum to you. If it’s very long, it will make a heavy object easier to lift, opposite if its shorter, but would cause object to move farther distance than you move.

Load Arm

Length from the fulcrum to the object

First class lever

Fulcrum in middle, can have any range of MA.

Second class lever

Load in middle, MA always above 1

Third class lever

Effort in the middle, MA is always below 1

First Class Lever example

the skull balances on the spine (fulcrum), the weight of the head (load) is mostly anterior, muscles in the back of the head/neck (effort) keep the head balanced

Second Class Lever example

body weight (load) rests on the center of the foot, the calf muscles (effort) pull via the achilles tendon at the heel, and pivot at the toes (fulcrum)

Third Class Lever example

Weights (load) held in the hand are lifted by the bicep muscles (effort) that insert on the proximal end of the radius, and pivot at the elbow (fulcrum)