Physics Chapter 2: Statics and Torque
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Questions and Answers

What is the applied external force required to topple an erect person, given the conditions described?

  • 400 N
  • 377.3 N
  • 250 N
  • 314.42 N (correct)

    • What is the weight of the pole mentioned in the example calculated in Newtons?

  • 9.8 N
  • 49 N
  • 5 N
  • 19.6 N (correct)

    • What distance from the right hand does the center of gravity of the pole lie, if the hands are 0.9 m apart?

  • 0.6 m
  • 0.9 m
  • 1.2 m
  • 0.3 m (correct)

    • In the calculation of torque, what angle was assumed for the hands' force application?

    <p>90 degrees</p> Signup and view all the answers

    What is the relationship between the torques produced by the right hand and the weight of the pole?

    <p>τR = -τw</p> Signup and view all the answers

    What is the restoring torque created by the person's weight if the weight is 70 kg?

    <p>377.3 N.m</p> Signup and view all the answers

    What distance does the applied force operate from the pivot point in the first example?

    <p>1.2 m</p> Signup and view all the answers

    What does the force exerted by the right hand equal based on the given calculations?

    <p>32.7 N</p> Signup and view all the answers

    What is the formula for calculating torque?

    <p>$ au = rF imes ext{sin} heta$</p> Signup and view all the answers

    What condition must be met for a body to be in static equilibrium?

    <p>The resultant external force must equal zero.</p> Signup and view all the answers

    What does the center of mass represent in an object under constant gravity?

    <p>The average position of all mass parts.</p> Signup and view all the answers

    What occurs when the center of mass is directly over the base of support?

    <p>The object is in stable equilibrium.</p> Signup and view all the answers

    What happens if the resultant external torque does not equal zero?

    <p>The body will rotate.</p> Signup and view all the answers

    In the right-hand rule, what does the thumb represent?

    <p>The direction of the torque.</p> Signup and view all the answers

    What characterizes a body in stable equilibrium?

    <p>The reaction force cancels the weight of the body.</p> Signup and view all the answers

    How is torque expressed in units?

    <p>Newton-meters (N.m)</p> Signup and view all the answers

    What is the equation derived from Newton’s second law for the forces in equilibrium?

    <p>FL + FR = mg</p> Signup and view all the answers

    What is the calculated force exerted by the left hand (FL) if the weight of the bar is 5 kg?

    <p>16.3 N</p> Signup and view all the answers

    What is defined as the fixed point around which a lever rotates?

    <p>Fulcrum</p> Signup and view all the answers

    In levers, what is the term for the force that is applied to the lever?

    <p>Input force</p> Signup and view all the answers

    Which equation represents the torque balance in a lever at equilibrium?

    <p>F d2 = W d1</p> Signup and view all the answers

    What determines the amount of force exerted by a muscle?

    <p>The number of fibers contracting</p> Signup and view all the answers

    What is the mechanical advantage of a lever defined as?

    <p>The ratio of load to applied force</p> Signup and view all the answers

    Which of the following forces would apply when calculating FL based on the bar's weight?

    <p>Gravity acting on the bar</p> Signup and view all the answers

    What happens to a body when its center of mass is above its base?

    <p>The reaction force tries to restore the body to its original position.</p> Signup and view all the answers

    Where is the center of gravity of an erect person with arms at their side located?

    <p>Approximately 56% of the person's height.</p> Signup and view all the answers

    What occurs when a person carries an uneven load?

    <p>The center of gravity shifts towards the heavier side.</p> Signup and view all the answers

    What is the gravitational acceleration used for calculations involving human weight?

    <p>9.8 m/s²</p> Signup and view all the answers

    What is the relation between the anti-clockwise torque and the restoring torque when a person is about to fall?

    <p>Both torques are equal.</p> Signup and view all the answers

    For a person with a mass of 70 kg, what is the force required to topple them when standing at rigid attention?

    <p>45.7 N</p> Signup and view all the answers

    What can happen to amputees who do not use artificial limbs?

    <p>They may experience permanent spinal distortion.</p> Signup and view all the answers

    What is affected when a body’s shape changes, despite the mass remaining the same?

    <p>The center of mass.</p> Signup and view all the answers

    Study Notes

    Principles of Physics

    • Presented by Dr. Mohaned Mohammed, School of Biotechnology, Badr University, Assiut.
    • Introduces the concepts of Statics and Torque.

    Chapter Two: Statics and Torque

    • Focuses on the principles of Statics and Torque in physics.

    Torque

    • The magnitude of torque (τ) equals the applied force (F) times the length of the arm (r) perpendicular to the force.
    • |τ| = |F × r| = rF sin θ, where θ is the angle between the force and the direction of r.
    • Torque is zero if the force passes through the pivot point.
    • The force (F) is measured in Newtons (N), and torque is measured in Newton-meters (N⋅m).
    • The direction of torque can be determined using the right-hand rule.

    Static Equilibrium

    • A body is considered in mechanical equilibrium if two conditions are met:
      • The resultant external force equals zero (ΣF = 0).
      • The resultant external torque equals zero about any axis (Στ = 0).
    • If these conditions aren't met, the body will rotate.
    • A body is static if its linear and angular velocities are zero.

    Conditions for Static Equilibrium

    • The center of mass is the average position of an object's parts, weighted by their masses.
    • For a body to be in stable equilibrium under gravity, the center of mass must be directly above the base of support.
    • In a stable body, the reaction force (F₁) upwards cancels the body weight (Fw) downwards, acting along the same line with opposite directions.
    • Unstable bodies rotate around a pivot point.

    Equilibrium in the Human Body

    • The center of gravity for an upright person with their arms at their sides is approximately 56% of their height from the soles of their feet.
    • The center of mass changes position if the shape of the body changes, even if the mass remains constant.
    • The body compensates for uneven loads by adjusting limb positions to keep the center of gravity balanced over the feet.
    • Amputees may need prosthetic limbs to help maintain stability.

    The Action of an External Force on Human Body Stability

    • Example illustrating calculating the force required to cause a person to topple while standing at attention.
    • Calculates this using torques applied to the body.

    Example 2

    • Calculates the force required to topple a person in a standing position, accounting for their mass, height, and foot width.

    Example 3

    • Calculates the force each hand exerts to hold a pole in a balanced position, given the weight of the pole and the distance from the hands to the center of gravity of the pole.

    Muscles

    • Skeletal muscles consist of numerous parallel fibers.
    • Muscle force depends on the number of contracting fibers.
    • Tendons connect muscles to bones.
    • Most muscles end in a single tendon, except biceps and triceps.

    Levers

    • A lever is a rigid bar that rotates around a fixed point called the fulcrum.
    • Levers have three components: fulcrum, input force (effort), and output force (load).
    • Levers are useful for moving or lifting loads.
    • There are three classes of levers:
      • Class 1: Fulcrum is between the input and output forces (e.g., claw hammer).
      • Class 2: Output force is between the input force and the fulcrum (e.g., wheelbarrow).
      • Class 3: Input force is between the output force and the fulcrum (e.g., human arm).

    Forces and Torques in Muscles and Joints

    • Skeletal muscles generate forces significantly larger than forces applied to the limbs.
    • This is because tendons attach close to joints, providing mechanical advantage in transferring force.

    Example

    • Calculates the force required from the biceps muscle to hold a forearm and load.
    • Compares the calculated force to the combined weight of the forearm and load.

    Discussion

    • The biceps exerts 7.38 times the supported weight.
    • Changing the angle between the forearm and upper arm affects the biceps force.
    • The force is variable depending on biceps muscle length.

    Example

    • Calculates the force needed in the back muscles to support an upper body and box.
    • Calculates the force exerted by the vertebrae at the pivot point.

    Problem Solving Strategy

    • A free body diagram is used to visualize all the forces acting on the body.
    • The net force must be zero (ΣF= 0).
    • The net torque must be zero (Σt = 0).

    Problem 9.32

    • Calculates the force needed by the neck muscles to keep the head held erect.
    • Determining the force exerted by the head's pivot point.

    Problem 12.41

    • Determining the magnitudes (tension) in the deltoid muscle of the arm.
    • Determining the magnitude of the shoulder's force acting on the upper arm.

    Problem 12.42

    • Finding values of T, R, and u (position) for a person standing on tiptoe with a given gravitational force acting on them.

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    Principles of Physics Chapter 2 PDF

    Description

    Explore the fundamental concepts of Statics and Torque in this quiz based on Chapter Two of the Principles of Physics. Understand the calculations of torque, the conditions for static equilibrium, and the application of the right-hand rule. Test your knowledge on these essential physics principles.

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