Torque and Moment Arm in Mechanics

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Questions and Answers

What is the formula for calculating torque?

T = rFsin(θ) (correct)

T = rFcos(θ)

T = r/F

T = rFtan(θ)

What relationship does the moment arm have with the angle of force application?

It decreases as the angle approaches 90 degrees.

It increases as the angle approaches 90 degrees. (correct)

It is independent of the angle of application.

It varies inversely with the angle of application.

When does gravity exert its maximum torque on a body segment?

When the segment is angled at 45 degrees.

When the segment is inclined upwards.

When the segment is parallel to the ground. (correct)

When the segment is upright.

What defines the moment arm in the context of muscle force?

The length of a line from the force vector to the joint axis. Signup and view all the answers

How does the resistance arm created by gravity on the center of gravity affect torque?

It affects the amount of torque based on the position of the muscle. Signup and view all the answers

Which statement is accurate regarding the composition of forces acting on a human body?

Gravity is a vital contributing force in body movement. Signup and view all the answers

What term describes the distance from the axis to where force is applied to a lever?

Lever Arm Signup and view all the answers

What happens to torque when the moment arm is minimized?

Torque is minimized. Signup and view all the answers

What is the definition of the effort force in a lever system?

The force that causes the rotation of the lever Signup and view all the answers

Which of the following statements is true regarding the mechanical advantage of levers?

A longer effort arm compared to the resistance arm results in greater mechanical advantage Signup and view all the answers

What type of lever has the effort force applied closer to the axis than the resistance force?

Third-class lever Signup and view all the answers

In which type of lever do both parallel forces create rotation in opposite directions?

First-class lever Signup and view all the answers

If the resistance arm is significantly longer than the effort arm, what can be expected regarding mechanical advantage?

Mechanical advantage will be less than 1 Signup and view all the answers

Which component of the lever is specifically defined as the axis or the point where rotation occurs?

Fulcrum Signup and view all the answers

Which type of lever is most effective for lifting heavy loads with less effort, as indicated by a mechanical advantage greater than 1?

Second-class lever Signup and view all the answers

What is the term used to describe the ability of any force to cause rotation of the lever?

Torque Signup and view all the answers

What is the net torque acting on the lever when analyzing the forces while extending the elbow with a weight in the hand?

–55 in-lb Signup and view all the answers

Which direction does the biceps exert torque on the forearm when flexing?

Counterclockwise Signup and view all the answers

What type of muscle contraction occurs when a muscle shortens while moving the segment in the direction of its pull?

Concentric contraction Signup and view all the answers

What is the torque exerted by gravity on the forearm if the force of gravity is 10 lb and the distance from the axis is 10 in?

–100 in-lb Signup and view all the answers

During which type of contraction are muscles neither shortening nor lengthening?

Isometric contraction Signup and view all the answers

How can the net rotation of a lever be determined?

By finding the sum of all the torques acting on the lever Signup and view all the answers

What is the calculated torque exerted by the weight of the ball which has a weight of 5 lb and distance of 15 in?

–75 in-lb Signup and view all the answers

What happens when the sum of all torques acting on the lever is zero?

The lever will not rotate Signup and view all the answers

Study Notes

Torque

Torque refers to the force required by a muscle contraction to cause rotation at a joint.
Calculated as the product of force magnitude, distance from the axis of rotation, and the sine of the angle between the force vector and the lever arm.
Typically, the angle is 90 degrees.
Formula: Torque (T) = r * F * sin(θ)

Moment Arm

The moment arm of a force is the perpendicular distance from the force vector to the axis of rotation.
The moment arm length is determined by the angle of application of the force.
Lever Arm (LA): The distance from the axis of rotation to the point where the force is applied.
The moment arm of gravity depends on the position of the body segment, exerting maximum torque when the segment is parallel to the ground.

Composition of Forces

When a muscle contracts, such as the biceps, it produces a torque in the direction of contraction.
Gravity applies a torque in the opposite direction.
Example: When flexing the elbow, the biceps produces a positive torque (counterclockwise), while gravity produces a negative torque (clockwise).
Net torque is the sum of individual torques.
If the net torque is zero, the lever remains balanced.

Types of Muscle Contractions

Concentric: Muscle shortens, acting as the effort force.
Eccentric: Muscle lengthens, acting as the resistance force.
Isometric: Muscle remains the same length, as the lever is in rotational equilibrium.

Lever Terminology

Effort Force: Causes rotation of the lever.
Resistance Force: Opposes rotation of the lever.
Fulcrum: The axis of rotation.
Effort Arm (EA): Distance from the effort force to the fulcrum.
Resistance Arm (RA): Distance from the resistance force to the fulcrum.

Lever Principle

The ratio of the effort arm to the resistance arm determines the mechanical advantage (MA).
MA = EA / RA.
A higher mechanical advantage means less effort is needed to move a load.

Types of Levers

First Class Levers: Effort and resistance forces are on opposite sides of the fulcrum. MA can be greater than, less than, or equal to 1.
Second Class Levers: Effort force is farther from the fulcrum than the resistance force. MA is always greater than 1.
Third Class Levers: Effort force is closer to the fulcrum than the resistance force. MA is always less than 1.

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Description

This quiz explores the concepts of torque and moment arms, focusing on how muscle contractions generate rotation at joints. Understand the calculations and implications of force application and angles in biomechanics, particularly during movements like elbow flexion.