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College Physics (Urone)
Found in: Page 315
College Physics (Urone)

College Physics (Urone)

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

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Short Answer

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 by Step Solution

TABLE OF CONTENTS :
TABLE OF CONTENTS

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,

FoFi=IiIo

Here F∘ is the output force,Fi input force, l∘is the distance of output force from the joint, and li 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,

li<I∘

So,

Fi>Fo

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

Most popular questions for Physics Textbooks

(a) What is the mechanical advantage of a wheelbarrow, such as the one in Figure \({\rm{9}}{\rm{.24}}\), if the center of gravity of the wheelbarrow and its load has a perpendicular lever arm of \({\rm{5}}{\rm{.50}}\;{\rm{cm}}\), while the hands have a perpendicular lever arm of \({\rm{1}}{\rm{.02}}\;{\rm{m}}\)? (b) What upward force should you exert to support the wheelbarrow and its load if their combined mass is\({\rm{55}}{\rm{.0}}\;{\rm{kg}}\)? (c) What force does the wheel exert on the ground?

Suppose you pull a nail at a constant rate using a nail puller as shown in Figure 9.23 . Is the nail puller in equilibrium? What if you pull the nail with some acceleration – is the nail puller in equilibrium then? In which case is the force applied to the nail puller larger and why?

We analyzed the biceps muscle example with the angle between forearm and upper arm set at 90o. Using the same numbers as in Example 9.4, find the force exerted by the biceps muscle when the angle is 120o and the forearm is in a downward position.

Question: Unreasonable Results

Suppose two children are using a uniform seesaw that is 3.00m long and has its center of mass over the pivot. The first child has a mass of and sits from the pivot. (a) Calculate where the second 18.0kg child must sit to balance the seesaw. (b) What is unreasonable about the result? (c) Which premise is unreasonable, or which premises are inconsistent?

Explain why the forces in our joints are several times larger than the forces we exert on the outside world with our limbs. Can these forces be even greater than muscle forces?
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