Physics 15 Torque Example 5 (5 of 7) The Bicep

Michel van Biezen

7 Apr 201306:45

EducationalLearning

32 Likes 10 Comments

TLDRThe video script presents a fascinating exploration of torque problems as they relate to the human body, specifically focusing on the bicep muscle. It explains how the bicep functions in lifting a barbell, taking into account the muscle's attachment points and the leverage effect. The presenter uses the example of lifting a 40-pound barbell to illustrate the concept of torque, which is the force required to produce rotation around a pivot point—in this case, the elbow joint. By calculating the force exerted by the bicep, the video reveals that lifting the barbell requires a surprising 363 pounds of force from the bicep, demonstrating the remarkable strength of human muscles. The script is an engaging and informative look into the physics of everyday human movements.

Takeaways

💡 The biceps muscle plays a crucial role in lifting the arm and is connected to the humerus and forearm bone at different distances from the elbow joint.
🏋️‍♂️ When lifting a weight, such as a barbell, the bicep muscle has to work harder to overcome the force of gravity and the weight of the forearm itself.
📐 The problem presented is a torque problem, which involves calculating the force required by the bicep to lift a barbell by considering the distances and weights involved.
⚖️ The sum of all torques about the pivot point (the elbow joint) must equal zero, which is a fundamental principle in statics.
🔢 The force exerted by the bicep is calculated using the formula that takes into account the weight of the barbell, the weight of the forearm, and the distances from the pivot point to the points of force application.
🤔 The angle between the bicep's pull and the line of action is ignored due to its small size, simplifying the calculation.
📏 The distances used in the calculation are critical, with the forearm's center of mass assumed to be at the halfway point between the hand and the elbow joint.
🏋️‍♀️ The force required by the bicep to lift a 40-pound barbell is found to be 363 pounds, which is significantly higher than the actual weight being lifted.
😮 This result highlights that our muscles, particularly the bicep, are much stronger than we might initially perceive.
🧮 The units used in the calculation (pounds and centimeters) are mixed but will cancel out, leaving the final answer in pounds, which is the unit for force.
📉 The weight of the forearm and the barbell both contribute to the positive torque, while the bicep's force contributes to the negative torque, as it acts in the opposite direction.
🔍 The example demonstrates the application of physics principles to understand the mechanics of human movement and the forces involved in everyday activities.

Q & A

What is the primary focus of the example provided in the script?
-The primary focus is to demonstrate how to calculate the force required on the bicep when lifting a barbell using torque problems related to the human body.
What is the role of the bicep muscle in lifting a weight?
-The bicep muscle is responsible for lifting the arm up against gravity when a weight is held in the hand, such as during a barbell exercise.
What are the three forces considered in the torque problem?
-The three forces considered are the weight of the barbell (big mg), the weight of the forearm (little mg), and the force exerted by the bicep muscle.
What is the significance of the pivot point in the torque problem?
-The pivot point, in this case the elbow joint, is the point around which the torques are calculated. It is the reference point from which the perpendicular distances to the lines of action of the forces are measured.
Why is the angle between the bicep and the forearm ignored in the calculation?
-The angle is ignored because it is almost straight up, making it small and not significantly affecting the calculation of the force required by the bicep.
What units are used in the calculation and how are they handled?
-Pounds and centimeters are used in the calculation. The units of centimeters cancel out when dividing by the distance (d3), leaving the unit for force in pounds.
What is the calculated force on the bicep when lifting a 40-pound barbell?
-The calculated force on the bicep is 363 pounds, which is significantly more than the actual weight of the barbell being lifted.
What is the assumption made about the center of mass of the forearm?
-The assumption is that the center of mass of the forearm is at the halfway point between the middle of the hand (palm) and the elbow joint.
How does the distance from the elbow joint to where the barbell is held affect the force on the bicep?
-The distance (d1) affects the force on the bicep as it is part of the calculation for the torque caused by the weight of the barbell.
What is the role of gravity in this scenario?
-Gravity aids in bringing the arm back down after it has been lifted by the bicep, but it does not contribute to the lifting action itself.
Why is the force exerted by the bicep higher than the weight of the barbell?
-The force exerted by the bicep is higher because it has to overcome the torque created by the weight of the barbell and the weight of the forearm, in addition to lifting the barbell itself.
What does this example illustrate about the strength of human muscles?
-This example illustrates that human muscles, such as the bicep, are much stronger than one might think, as they can exert a force significantly greater than the weight they are lifting.

Outlines

00:00

💪 Understanding Bicep Torque in Lifting Weights

The first paragraph introduces the concept of torque problems related to the human body, specifically focusing on the bicep muscle. It explains how the bicep's position relative to the elbow joint creates leverage, which requires the bicep to exert significant force when lifting weights. The paragraph outlines a mathematical problem to calculate the force exerted by the bicep when lifting a 40-pound barbell, taking into account the weight of the forearm, the distance from the elbow joint to the point where the barbell is held, and the center of mass of the forearm. The problem is set up using torque principles, where the sum of all torques around the elbow joint equals zero, and the forces considered include the weight of the barbell, the weight of the forearm, and the force exerted by the bicep. The paragraph concludes by emphasizing the surprising strength of the bicep in performing this task.

05:01

📐 Calculating the Actual Force on the Bicep

The second paragraph continues the discussion on torque and force, providing a solution to the problem introduced in the first paragraph. It explains the process of calculating the force required by the bicep to lift a 40-pound barbell, including the conversion of units from pounds to the force's unit. The paragraph walks through the calculation, factoring in the distances from the pivot point (elbow joint) to the points of force application (barbell and forearm's center of mass) and the attachment point of the bicep. The final calculation reveals that the bicep must exert a force of 363 pounds to lift the barbell, which is significantly higher than the actual weight being lifted, underscoring the strength of the human musculature. The paragraph concludes by inviting the reader to contemplate the surprising strength of their muscles.

Mindmap

Keywords

💡Torque

Torque is the rotational force that tends to cause rotation about an axis. In the video, it is used to explain how the force exerted by the bicep muscle contributes to the lifting of a barbell. The concept is central to understanding the physics problem presented, as it involves calculating the force required for the bicep to lift the weight.

💡Biceps

The bicep is a muscle located on the front of the upper arm. In the context of the video, the bicep's role is to generate the force necessary to lift a barbell. The force exerted by the bicep is a key factor in the torque problem being solved, highlighting the muscle's importance in physical exertion.

💡Barbell

A barbell is a long, rigid bar of metal, wood, or other material, used in weightlifting and bodybuilding. In the video, a barbell with a weight of 40 pounds is used as an example to illustrate the force exerted by the bicep. The barbell serves as the resistive force that the bicep must overcome to perform the lifting action.

💡Elbow Joint

The elbow joint is the hinge joint that connects the forearm to the upper arm. In the video, it is chosen as the pivot point around which the torques are calculated. The position of the elbow joint is critical in the analysis of the forces acting on the arm during the lifting of the barbell.

💡Torque Problem

A torque problem involves calculating the net torque acting on an object, which is the sum of all the torques about a specific pivot point. In the video, the torque problem is used to determine the force required by the bicep to lift the barbell, with the sum of torques around the elbow joint equating to zero.

💡Pivot Point

The pivot point is the point around which a body rotates or扭扭转. In the context of the video, the elbow joint is chosen as the pivot point for calculating the torques acting on the arm. The pivot point is essential in the torque problem as it is the reference point for measuring distances and calculating torques.

💡Distance (d1, d2, d3)

Distances d1, d2, and d3 are the perpendicular distances from the pivot point to the line of action of the forces acting on the arm. In the video, these distances are crucial in calculating the torques produced by the barbell weight, the forearm weight, and the bicep force, respectively. The distances are used in the equation to find the force on the bicep.

💡Center of Mass

The center of mass is the point at which the mass of an object may be considered to be concentrated for the purpose of analyzing its motion. In the video, the center of mass of the forearm is assumed to be at the halfway point between the hand and the elbow joint. This assumption is used to calculate the torque produced by the weight of the forearm.

💡Weight

Weight is the force exerted on a mass due to gravity. In the video, the weight of the barbell and the forearm are given in pounds and are used to calculate the gravitational force acting on them. The weight of the barbell is a primary factor in determining the force required by the bicep to lift it.

💡Force

Force is any interaction that causes an object to change its velocity, which includes changes in speed or direction of motion. In the video, the force exerted by the bicep is the unknown variable that needs to be calculated. The force is central to solving the torque problem and understanding the physical effort involved in lifting the barbell.

💡Counterclockwise and Clockwise

These terms describe the direction of rotation around an axis. In the context of the video, a positive torque is associated with a clockwise rotation, while a negative torque is associated with a counterclockwise rotation. The direction of the torques is important for setting up the correct equation to solve for the force on the bicep.

Highlights

Explains how to use torque problems to analyze the force required on the bicep when lifting a barbell

Provides a detailed example using the biceps, forearm, and upper arm of a person

Describes the anatomy of the bicep and its attachment points to the humerus and forearm bone

Calculates the force the bicep needs to exert to lift a 40 pound barbell using torque equations

Assumes the forearm weighs 3 pounds and the distance from the elbow joint to the barbell is 35 cm

Uses the center of mass of the forearm as the halfway point between the hand and elbow joint

Sets the pivot point of the torque problem at the elbow joint

Identifies the forces acting on the elbow joint - weight of the barbell, weight of the forearm, and bicep force

Derives the equation for the force on the bicep by summing the torques to zero and solving for the bicep force

Plugs in the given values for the barbell weight, forearm weight, distances, and bicep attachment point

Calculates the force the bicep needs to exert is 363 pounds, much higher than the actual weight lifted

Highlights that our muscles are much stronger than we think

Demonstrates the practical application of torque problems in biomechanics and human anatomy

Provides a step-by-step walkthrough of the problem-solving process

Uses assumptions and simplifications to make the problem more tractable

Explains the concept of positive and negative torques and their directions

Shows how to set up and solve a torque problem using basic physics principles

Visualizes the problem using a drawing to help convey the key concepts

Provides an engaging and accessible introduction to torque problems and their applications

Transcripts

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Physics 15 Torque Example 5 (5 of 7) The Bicep

Takeaways

Q & A

What is the primary focus of the example provided in the script?

What is the role of the bicep muscle in lifting a weight?

What are the three forces considered in the torque problem?

What is the significance of the pivot point in the torque problem?

Why is the angle between the bicep and the forearm ignored in the calculation?

What units are used in the calculation and how are they handled?

What is the calculated force on the bicep when lifting a 40-pound barbell?

What is the assumption made about the center of mass of the forearm?

How does the distance from the elbow joint to where the barbell is held affect the force on the bicep?

What is the role of gravity in this scenario?

Why is the force exerted by the bicep higher than the weight of the barbell?

What does this example illustrate about the strength of human muscles?