Ch.5 Torque

What is torque?

- rotation effect produced by the eccentric force

What is eccentric force?

- force that does not go through center of object’s mass or axis of rotation

What is the torque produced by the force determined by?

- magnitude of force applied
- length of its moment arm

What will increase the magnitude of torque produced by the force?

- magnitude of force increases
- moment arm increases

What is the moment arm?

- perpendicular distance between force’s line of action and axis of rotation

What direction can torque go?

- + (counter-clockwise)
- - (clockwise)

What factors affect the moment arm length?

- distance between axis and point of force application (increase distance, increase length)
- direction of force application (perpendicular direction, longer arm)

What is net torque?

- sum of all torques acting about the axis
- determines direction of angular acceleration

What does net torque allow us to understand?

- combined effects of torques acting about axis

Why do we participate in resistance training?

- we are challenging muscle to produce progressively greater force by increasing torque produced by resistance

How might we adjust the resistance to make the exercise harder?

- increase torque produced by resistance by increasing moment arm and/or force of resistive force

How might we adjust the resistance to make the exercise easier?

- decrease torque produced by resistance by decreasing moment arm and/or the force of resistive force

What are some ways to increase the magnitude of resistance?

- use heavier weights
- use resistive bands with greater stiffness

How do muscles overcome the torque produced by resistive force?

- produce torque

Characteristics of moment arm of muscle

- tends to be very short since muscles tend to insert close to joints

What is a lever?

- a system with a beam sitting on an axis with 2 forces (motive force & resistive force) acting on it

What is motive force (Force)?

- input force applied to the lever with an effort to rotate the lever

What is resistive force (Resistance)?

- load that motive force must overcome to rotate the lever

What is the axis?

- fulcrum in which lever rotates

What is the lever arm?

- distance between axis of rotation and point of force
- deals with forces perpendicular to beam
- aka the moment arm

What does it mean when the longer the lever arm is?

- the more torque produced by the force

What is the 1st class lever?

- 2 forces are applied on the opposite sides of fulcrum
- Force —— Axis ——- Resistance (FAR)

What is the 2nd class lever?

- 2 forces are applied on same side of fulcrum, resistive force is closer to axis than motive force
- rare in body
- Axis ——- Resistance ——- Force (ARF)

What is the 3rd class lever?

- 2 forces applied on same side of fulcrum, motive force is closer to axis than resistive force
- most common type
- Axis ——- Force ——- Resistance (AFR)

What determines how effective which force (motive or resistance) will be?

- the length of the lever arm (longer, more effective)

What is a mechanical advantage?

- ratio of lever arms of motive force and resistive force
- motive lever arm / resistive lever arm
- more than 1, more effective, uses less effort

Does 2nd class lever have a high mechanical advantage?

- yes, lever arm of motive force is always longer than lever arm of resistive force
- always more than 1

Does 3rd class lever have a high mechanical advantage?

- no, lever arm of motive force is always shorter than lever arm of resistive force
- always less than 1

Does 1st class lever have a high mechanical advantage?

- depends where fulcrum is located
- can be more than 1 or less than 1

What does it mean to have a mechanical advantage less than 1?

- muscles (motive force) needs to work harder to go overcome torque produced by resistive force

What does it mean to have a mechanical advantage more than 1?

- muscles (motive force) can overcome the torque produced by resistive force with “less effort”

What does it mean when the lever arm of the motive force is longer than the lever arm of resistive force?

- mechanical advantage is more than 1
- mechanically efficient
- motive force can be smaller than resistive force to overcome resistive torque

What does it mean when the lever arm of the motive force is shorter than the lever arm of resistive force?

- mechanical advantage is less than 1
- mechanically inefficient
- motive force needs to be greater than resistive force to overcome the resistive torque

Why is a slouched posture bad for your neck?

- posture will increase torque produced by head weight and decreases mechanical advantage of neck extensors
- will increase force neck extensors must produce to maintain posture

What is the advantage of the 3rd class lever system for muscles?

- muscles having a shorter lever arm allows the muscle to move the joint through a greater ROM