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Found in: Page 315

### College Physics (Urone)

Book edition 1st Edition
Author(s) Paul Peter Urone
Pages 1272 pages
ISBN 9781938168000

# Why are the forces exerted on the outside world by the limbs of our bodies usually much smaller than the forces exerted by muscles inside the body?

The limbs are the third-class lever, so the forces exerted on the outside world by the limbs of our bodies are usually much smaller than the forces exerted by muscles inside the body

See the step by step solution

## Step 1: The given information

The forces exerted on the outside world by the limbs of our bodies.

The forces exerted by muscles inside the body.

## Step 2: The concept of Mechanical Advantage

For a lever, the mechanical advantage is,

$\frac{{\mathbf{F}}_{\mathbf{o}}}{{\mathbf{F}}_{\mathbf{i}}}{\mathbf{=}}\frac{{\mathbf{I}}_{\mathbf{i}}}{{\mathbf{I}}_{\mathbf{o}}}$

Here ${{\mathbit{F}}}_{{\mathbf{\circ }}}$ is the output force,${{\mathbit{F}}}_{{\mathbf{i}}}$ input force, ${{\mathbit{l}}}_{{\mathbf{\circ }}}$is the distance of output force from the joint, and ${{\mathbit{l}}}_{{\mathbf{i}}}$ is the distance of the input from the joint.

## Step 3: Analysis of the forces

Let the load is on the palm of a person’s hand. The fulcrum is the elbow joint, then. The biceps muscles exert the required input force.

In the case of the human hand, holding an object, the input force is at a closer distance from the fulcrum than the output force; we can write,

${l}_{i}<{I}_{\circ }$

So,

${F}_{i}>{F}_{o}$

Hence, the input force is greater than the output force.