Physics - week 4 & 5

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Questions and Answers

What factor determines the amount of mechanical advantage provided by a lever?

The distance from effort to the fulcrum compared to the distance from load to the fulcrum (correct)
The weight of the load being lifted
The angle of the lever's inclination
The type of material used to construct the lever

In a second class lever, how is the distance of the resistance force to the fulcrum compared to the effort force?

It is equal to the distance of the effort force.
It does not affect the mechanical advantage.
It is closer than the distance of the effort force. (correct)
It is farther than the distance of the effort force.

Which type of lever requires more force to lift, but allows the object to move further?

Third class lever (correct)
Second class lever
First class lever
Compound lever

What is the main purpose of using a lever in mechanical systems?

To multiply the force applied (D) Signup and view all the answers

Which of the following statements about effort and resistance forces in levers is incorrect?

The resistance force assists in lifting the load. (D) Signup and view all the answers

What describes the torque produced by a force in a lever system?

The ability of any force to cause rotation around the fulcrum (B) Signup and view all the answers

What is the resultant torque when opposing torques from the biceps and gravity are considered?

20 in-lb in a counterclockwise direction (D) Signup and view all the answers

Which type of contraction occurs when the biceps is actively shortening during flexion of the forearm?

Concentric contraction (B) Signup and view all the answers

When the lever is in rotational equilibrium, which statement is accurate?

Muscles are neither shortening nor lengthening (A) Signup and view all the answers

What is the total torque acting on the lever when all forces are considered?

−55 in-lb (D) Signup and view all the answers

In the context of muscle force, how does gravity affect the forearm's rotation?

It exerts a torque in a clockwise direction (A) Signup and view all the answers

Which component does NOT contribute to the net torque when extending the elbow with weight in hand?

Weight of forearm (D) Signup and view all the answers

What is the lever arm for the muscle force of biceps during the calculation?

1 inch (B) Signup and view all the answers

How does the torque exerted by the weight of the ball influence the overall torque on the arm?

It contributes negatively to the net torque (A) Signup and view all the answers

What direction does the torque exerted by the biceps act upon the forearm?

Counterclockwise direction (D) Signup and view all the answers

What is the relationship between torque and moment arm?

Torque is the product of force and moment arm length. (A) Signup and view all the answers

In which condition is the moment arm considered to be the greatest?

When the angle of the applied force is 90 degrees. (A) Signup and view all the answers

What changes to the moment arm occurs when a lever is parallel to the ground?

The gravitational force creates maximum torque in this position. (C) Signup and view all the answers

Which formula correctly represents the calculation of net force when flexing the elbow with the biceps contracting?

Net force equals the product of force and moment arm. (D) Signup and view all the answers

What describes the lever arm in relation to torque?

The lever arm represents the distance from the axis to the point of force application. (D) Signup and view all the answers

Which statement about mechanical advantage is true?

Mechanical advantage decreases the effort needed for the same amount of work. (A) Signup and view all the answers

How does the angle of force application affect the moment arm?

The moment arm is largest when the force is applied perpendicular to the lever. (A) Signup and view all the answers

What role does gravity play concerning the resistance arm created on the center of gravity?

Gravity provides maximum torque at the point of application depending on lever position. (D) Signup and view all the answers

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Study Notes

Torque and Moment Arms

Torque is the force needed by a muscle to cause rotation at a joint, the product of force, distance, and the sine of the angle between them.
The Moment Arm is the distance from the joint axis to the force vector and is always perpendicular to the force.

Composition of Forces

In the human body, forces from muscles and gravity act on body segments.
The angle of application of force changes depending on the segment's orientation.
The net torque acting on a lever is the sum of all torques acting on the lever.

Mechanical Advantage

It is the ratio of the effort arm to the resistance arm (Effort Arm/Resistance Arm)
Levers magnify effort force, but the mechanical advantage depends on the lever's type and the location of the effort, load, and fulcrum.

Types of Levers

First Class: Fulcrum is between the resistance and the effort (MA can be >1, <1, or =1)
Second Class: Resistance is between the fulcrum and the effort (MA > 1, easier to lift)
Third Class: Effort is between the fulcrum and the resistance (MA < 1, harder to lift, but the object moves further)

Types of Muscle Contractions

Concentric: Muscle shortens, acts as the effort force
Eccentric: Muscle lengthens, acts as the resistance force
Isometric: Muscle neither shortens nor lengthens, the lever is in equilibrium.

Muscle Force and Gravity

Biceps and Gravity: When flexing the elbow, the biceps exerts a force of 120in-lb, while gravity exerts a force of -100in-lb. The net torque is +20in-lb, causing flexion of the forearm.
Extending the Elbow with a Weight: When extending the elbow with a weight, the forces acting are the biceps, gravity, and the weight of the ball. The net torque is -55in-lb, leading to extension of the forearm.

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