KINESIOL2241 BIOMECHANICS - Final Exam Concepts Review
Torques and Moments
1. What is a torque? What are the components of a torque? What are the effects of a
torque?
- Motion of a restrained system → has axis of rotation and one side fixed in space
- Directly proportional to magnitude and distance between line of action of force and axis
of rotation
- Components of torque: force and moment arm
- Produces a turning effect
- Can either be rotatory or non-rotatory
2. Compare a moment arm to a lever arm. Use a diagram to illustrate your answer.
- Moment arm: shortest distance between axis of rotation and line of action of force
- Perpendicular to line of action and axis of rotation
- Lever arm: distance between point of force application (perpendicular) and axis of
rotation
3. Where do we observe torques in humans? Compare concentric to eccentric muscle
action – use a diagram to illustrate your answer.
- Torques observed in joints
- Concentric: muscle internal moment and motion in same direction
- Eccentric: muscle internal moment and motion in opposite direction
4. Define the rotary and non-rotary components of a muscle force. Use a diagram to
illustrate your answer
- Rotatory: perpendicular to bone segment, creates internal moment, causes motion
- Non-rotatory: perpendicular to rotatory component, parallel to bone, does not
contribute to internal moment, causes joint compression or distraction
5. The moment/torque created by a muscle is dependent on what 3 things? What is the
influence of a longer moment arm on joint torques? Is this a good or bad thing?
Provide a scenario of when a longer moment arm would be advantageous and
disadvantageous.
- Muscle force (F), lever arm (d), and angle of pull (θ)
- Longer moment arm would cause more force being exerted on the joint
- The muscles of the joint would have to work harder to resist
- Advantageous: want to work out muscles
- Disadvantageous: has a higher destabilizing effect
6. Compare and contrast equilibrium and stability. How could you increase the stability
of human balance?
, - Equilibrium: state characterized by balanced forces and torques
- No net forces/torques
- Sum of all horizontal and vertical components are 0
- Sum of all torques are 0
- Stability: movement will occur but in a controlled manner
- Strengthen both the agonist and antagonist muscle to promote muscle
co-contraction
- Use external support → bracing or orthotics
- Reduce body mass
7. Describe different kinds of levers and provide an example of each from within the
human body.
- 1st class lever: axis between the motive force and resistive force (MAR)
- agonist/antagonist action
- Elbow extension
- Plantar flexion
- 2nd class lever: Resistance is in the middle between axis and motive force (ARM)
- Push up → feet = axis of rotation, resistive = center of body, motive force = arms
- 3rd class lever: motive force is in the middle between axis of rotation and resistive force
(AMR)
- Knee extension
- Most joint complexes → muscle is motive force
8. What is meant by a “mechanical advantage”? How might we use this information to
make it easier to lift a heavy object?
- Mechanical advantage = ratio of lever arm of motive force to lever arm of resistive force
- Motive force lever arm shorter than resistive force lever arm = increase MA
- Increases velocity
Angular Kinematics
1. Describe three units of measurement for angular position. What is a radian? What is
the major advantage of using radians to describe angular position?
- Degrees, revolutions/rotations, radians
- Radian = 57.3°
- Ratio of the arc length (r) of a circle to the radius length
- Determined in multiples of Pi
- Advantage: angular position is relative to a circle
2. Write the angular analogs to the calculation of linear distance/displacement,
speed/velocity, and acceleration.
Torques and Moments
1. What is a torque? What are the components of a torque? What are the effects of a
torque?
- Motion of a restrained system → has axis of rotation and one side fixed in space
- Directly proportional to magnitude and distance between line of action of force and axis
of rotation
- Components of torque: force and moment arm
- Produces a turning effect
- Can either be rotatory or non-rotatory
2. Compare a moment arm to a lever arm. Use a diagram to illustrate your answer.
- Moment arm: shortest distance between axis of rotation and line of action of force
- Perpendicular to line of action and axis of rotation
- Lever arm: distance between point of force application (perpendicular) and axis of
rotation
3. Where do we observe torques in humans? Compare concentric to eccentric muscle
action – use a diagram to illustrate your answer.
- Torques observed in joints
- Concentric: muscle internal moment and motion in same direction
- Eccentric: muscle internal moment and motion in opposite direction
4. Define the rotary and non-rotary components of a muscle force. Use a diagram to
illustrate your answer
- Rotatory: perpendicular to bone segment, creates internal moment, causes motion
- Non-rotatory: perpendicular to rotatory component, parallel to bone, does not
contribute to internal moment, causes joint compression or distraction
5. The moment/torque created by a muscle is dependent on what 3 things? What is the
influence of a longer moment arm on joint torques? Is this a good or bad thing?
Provide a scenario of when a longer moment arm would be advantageous and
disadvantageous.
- Muscle force (F), lever arm (d), and angle of pull (θ)
- Longer moment arm would cause more force being exerted on the joint
- The muscles of the joint would have to work harder to resist
- Advantageous: want to work out muscles
- Disadvantageous: has a higher destabilizing effect
6. Compare and contrast equilibrium and stability. How could you increase the stability
of human balance?
, - Equilibrium: state characterized by balanced forces and torques
- No net forces/torques
- Sum of all horizontal and vertical components are 0
- Sum of all torques are 0
- Stability: movement will occur but in a controlled manner
- Strengthen both the agonist and antagonist muscle to promote muscle
co-contraction
- Use external support → bracing or orthotics
- Reduce body mass
7. Describe different kinds of levers and provide an example of each from within the
human body.
- 1st class lever: axis between the motive force and resistive force (MAR)
- agonist/antagonist action
- Elbow extension
- Plantar flexion
- 2nd class lever: Resistance is in the middle between axis and motive force (ARM)
- Push up → feet = axis of rotation, resistive = center of body, motive force = arms
- 3rd class lever: motive force is in the middle between axis of rotation and resistive force
(AMR)
- Knee extension
- Most joint complexes → muscle is motive force
8. What is meant by a “mechanical advantage”? How might we use this information to
make it easier to lift a heavy object?
- Mechanical advantage = ratio of lever arm of motive force to lever arm of resistive force
- Motive force lever arm shorter than resistive force lever arm = increase MA
- Increases velocity
Angular Kinematics
1. Describe three units of measurement for angular position. What is a radian? What is
the major advantage of using radians to describe angular position?
- Degrees, revolutions/rotations, radians
- Radian = 57.3°
- Ratio of the arc length (r) of a circle to the radius length
- Determined in multiples of Pi
- Advantage: angular position is relative to a circle
2. Write the angular analogs to the calculation of linear distance/displacement,
speed/velocity, and acceleration.
