Physics 15 Torque (18 of 25) Body Mechanics: Ex. 6, F=? on Back Muscle

Michel van Biezen
26 Jan 201606:51
EducationalLearning
32 Likes 10 Comments

TLDRThe video script illustrates the importance of proper body mechanics when lifting heavy objects. It explains the concept using a hypothetical scenario where a person is bending over with a weight, highlighting the significant force exerted by the back muscles to maintain equilibrium. The script calculates the force required to keep the body balanced in this position, factoring in the weight of the torso, the additional weight being held, and the weight of the head. It emphasizes that even without any extra weight, the body's position puts an enormous strain on the back, which is why it's advised to keep the back straight to reduce torque and prevent injury. The final calculation reveals that the back muscle force needed is approximately 5,555 Newtons, or roughly 1,250 pounds, underscoring the immense strength required and the risks involved in improper lifting techniques.

Takeaways
  • ๐Ÿšซ **Incorrect Lifting Posture**: Bending over with a heavy weight is not recommended due to the immense strain it places on the back muscles.
  • ๐Ÿ‹๏ธโ€โ™‚๏ธ **Body Mechanics Importance**: Understanding body mechanics is crucial for safe lifting and preventing back injuries.
  • ๐ŸŽš๏ธ **Force Distribution**: The force exerted by the back muscles is calculated based on the weight of the body parts and their distances from the pivot point.
  • ๐Ÿงฎ **Calculating Torque**: Torque, the rotational force, is calculated by multiplying the force by the perpendicular distance from the force's line of action to the pivot point.
  • โš–๏ธ **Equilibrium Equation**: The sum of all torques acting on the body must equal zero for the body to be in equilibrium.
  • ๐Ÿ“ **Geometry of Lifting**: The script uses a triangle to determine the perpendicular distance (D) from the line of action of the force to the pivot point.
  • ๐Ÿ“‰ **Reducing Torque by Positioning**: Keeping the back straight reduces the torque angle, allowing for safer and more effective weight lifting.
  • ๐Ÿ’ช **Muscle Strength Required**: The back muscle must exert a significant force to maintain equilibrium in a bent-over position, which is calculated to be 5,555 Newtons or approximately 1,250 pounds.
  • ๐Ÿค” **Consideration of Head Weight**: The weight of the head, estimated to be around 100 Newtons, is factored into the overall force calculation.
  • ๐Ÿ“ **Length of the Back as a Reference**: The length of the back (L) is used as a reference to calculate the distances of various body parts' weights from the pivot point.
  • โ๏ธ **Avoiding Back Injury**: The advice to keep the back straight when lifting is reinforced by the high force required to lift in a bent position, highlighting the risk of back injury.
Q & A

  • What is the main topic discussed in the provided transcript?

    -The main topic discussed in the transcript is body mechanics, specifically focusing on the muscles in the back and the proper way to lift heavy weights to avoid injury.

  • Why is it not recommended to lift heavy weights with the back in a certain position?

    -Lifting heavy weights with the back in a certain position is not recommended because it puts an enormous amount of force on the back muscles, which can lead to injury.

  • What is the approximate weight of the upper part of the body in Newtons?

    -The approximate weight of the upper part of the body is about 300 Newtons.

  • How is the weight of the head estimated in Newtons?

    -The weight of the head is estimated to be around 100 Newtons, which is equivalent to approximately 5 pounds.

  • What is the significance of the pivot point in the context of the force applied by the back muscles?

    -The pivot point is significant because it is the point around which the torque is calculated. The force applied by the back muscles must counteract the torque from the weight of the body and any additional weight being lifted to maintain equilibrium.

  • What is the role of the back muscle in holding the body up when lifting a weight?

    -The back muscle, specifically the one attached about 2/3 of the distance from the pivot point to the attachment on the back, is responsible for holding the body up when lifting a weight.

  • How is the force required by the back muscle to keep the body in equilibrium calculated?

    -The force required by the back muscle is calculated by setting the sum of all torques acting on the body to zero, considering the weight of the torso, the weight being held, and the weight of the head, and then solving for the unknown force.

  • What is the approximate force in Newtons that the back muscle needs to apply to keep the body in equilibrium?

    -The approximate force that the back muscle needs to apply is 5,555 Newtons.

  • How is the force in Newtons converted to pounds?

    -The force in Newtons is converted to pounds by dividing by 4.44, since 1 pound is approximately equal to 4.44 Newtons.

  • What is the advice given to prevent back injuries when lifting weights?

    -The advice given is to keep the back straight, which reduces the torque angle and allows for better lifting mechanics, thus reducing the risk of back injury.

  • Why is it important to consider the torque and force when lifting weights?

    -Considering the torque and force is important because it helps to understand the physical demands on the body and to ensure that lifting is done in a way that minimizes the risk of injury.

  • What is the significance of the angle in the calculation of the force applied by the back muscle?

    -The angle is significant because it determines the perpendicular distance (D) from the line of action of the force to the pivot point, which is a factor in the torque calculation and thus affects the force required by the back muscle.

Outlines
00:00
๐Ÿ‹๏ธโ€โ™‚๏ธ Understanding Back Muscle Mechanics in Lifting

This paragraph discusses the mechanics of the back muscles when lifting weights. It emphasizes the incorrectness of bending over while lifting and the importance of maintaining an upright back to reduce the torque on the spine. The speaker uses a simplified illustration to explain the forces at play, including the weight of the upper body, the head, and the force required from the back muscles to maintain equilibrium. Mathematical calculations are provided to determine the force needed by the back muscles, considering the weight of the body and the distances from the pivot point. The explanation concludes with a formula that incorporates the sine of a 12-degree angle to find the perpendicular distance from the line of action of the force to the pivot point.

05:02
๐Ÿšซ The Risks of Poor Lifting Technique

The second paragraph calculates the force exerted by the back muscles when lifting in a poor posture. It demonstrates that even without adding extra weight, the body's position itself places a significant strain on the back. The speaker calculates the force required in newtons and then converts it to pounds to highlight the substantial strength needed to hold the body up in such a position. The paragraph concludes with advice to keep the back straight while lifting to reduce the risk of injury, as poor lifting technique can lead to back problems.

Mindmap
Keywords
๐Ÿ’กBody Mechanics
Body mechanics refers to the way the human body moves and the forces it exerts during physical activities. In the video, it is discussed in the context of lifting weights and the importance of proper posture to prevent back injuries. It is a central theme as it explains the physical principles behind safe lifting techniques.
๐Ÿ’กBack Muscles
Back muscles are the muscles located in the back that facilitate movement and support the spine. The video emphasizes the role of these muscles in lifting heavy objects and the potential strain they can experience if the body is not positioned correctly, which is crucial for understanding the importance of using proper body mechanics.
๐Ÿ’กBending Over
Bending over is a common action when lifting weights. The video script uses this action to illustrate the improper technique that can lead to back injuries. It is a key concept as it sets up the scenario for discussing the physics and biomechanics involved in safe lifting.
๐Ÿ’กWeights
Weights refer to the objects orๆ ้“ƒ (barbells) being lifted during strength training. In the context of the video, they represent the load that, when improperly lifted, can cause strain on the back muscles and potentially lead to injury. The discussion around weights is integral to understanding the risks and the need for correct body mechanics.
๐Ÿ’กNewtons
Newtons are a unit of force in the International System of Units (SI). In the video, Newtons are used to quantify the force exerted by the body's weight and the muscles during lifting. Understanding Newtons helps viewers grasp the magnitude of the forces involved in lifting and why proper technique is essential.
๐Ÿ’กTorque
Torque is a measure of the force that can cause an object to rotate about an axis. The video discusses the concept of torque to explain the rotational force acting on the spine when lifting weights improperly. It is a key concept in understanding why certain lifting positions can lead to back injuries.
๐Ÿ’กEquilibrium
Equilibrium in physics means a state in which all forces acting on an object are balanced, resulting in no net force. The video uses the concept of equilibrium to set up the equation that determines the force the back muscle needs to apply to support the body in a given position. It is central to the mathematical explanation provided in the video.
๐Ÿ’กPivot Point
A pivot point is a fixed point around which a body can rotate or turn. In the context of the video, the pivot point is the center of rotation for the body when lifting weights. Identifying the pivot point is essential for calculating the torque and force required to maintain balance.
๐Ÿ’กForce Application
Force application refers to how and where force is exerted to produce a desired effect, such as lifting a weight. The video explains that the force applied by the back muscles must be sufficient to counteract the torque produced by the body's weight. This concept is critical for understanding the physical demands of lifting and the potential for injury.
๐Ÿ’กStraight Back Position
Maintaining a straight back position is advised in the video as a safe way to lift weights. It is emphasized that keeping the back straight reduces the torque and force on the spine, thereby minimizing the risk of injury. This is a key piece of advice derived from the body mechanics discussed in the video.
๐Ÿ’กInjury Prevention
Injury prevention is the practice of avoiding harm or damage to the body. The video's main message revolves around injury prevention by explaining the biomechanics of lifting and the importance of using proper technique to avoid back injuries. It is the ultimate goal of understanding the concepts discussed in the video.
Highlights

The importance of proper body mechanics when lifting heavy weights is emphasized to prevent back injuries.

An example is given where a person is bending over and holding a weight, which is not recommended due to the strain on the back muscles.

The concept of torque and its role in body mechanics is introduced, explaining how the sum of torques must equal zero for equilibrium.

A mathematical model is used to calculate the force required for a back muscle to hold the body up in a bent position.

The weight of the body's upper part and head are considered in the calculation, with the head's weight estimated at 100 Newtons.

The force exerted by the back muscle is calculated using the sine of the angle between the muscle's line of action and the pivot point.

A triangle is used to visualize and solve for the perpendicular distance (D) from the force's line of action to the pivot point.

The final calculation reveals that the back muscle needs to exert a force of 5,555 Newtons, which is equivalent to approximately 1,250 pounds.

The transcript highlights the enormous amount of force required to hold the body in a bent position, even without additional weight.

The advice to keep the back straight is given to reduce the torque angle, making it easier and safer to lift weights.

The potential for back injury from improper lifting techniques is discussed, stressing the need for correct body mechanics.

The concept of the pivot point in body mechanics and its significance in maintaining equilibrium is explained.

A step-by-step mathematical approach is used to understand the forces involved in lifting, providing a practical application of physics to everyday activities.

The illustration of the person's body with labels for legs, back, arms, and head helps visualize the forces acting on the body during lifting.

The significance of the muscle's attachment point to the pivot point is discussed in relation to the force it needs to apply.

The transcript provides a clear demonstration of how improper lifting techniques can lead to back injuries due to the high forces involved.

The conversion of Newtons to pounds is done to cater to an audience that may be more familiar with the pound measurement of force.

The transcript concludes with a strong recommendation against lifting in a bent-over position due to the significant risk of back injury.

Transcripts

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Body MechanicsLifting SafetyMuscle StrengthBack InjuriesPhysical FitnessWeight TrainingHealth AdviceBiomechanicsExercise TechniqueInjury Prevention