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KNES 361 Exam 2 > Torques and Moments of Force > Flashcards

Torques and Moments of Force Flashcards

1
Q

What are Torques?

A

The turning effect produced by a force
Also called a moment
Think of it as an angular or rotary force
Directly proportional to the magnitude of force as well as the distance between the line of action of the force and the axis of rotation

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2
Q

Torque

A 
Motion of a restrained system
-Has an axis of rotation
-One side is fixed in space
Force is applied away from the axis
Line of action is not through the axis
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3
Q

Torque Force

A

Magnitude
Point of application
Direction
Line of action

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4
Q

Torque Moment Arm

A

Perpendicular distance between line of action of force and axis of rotation

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5
Q

Calculating Torque

A

T=Force x Moment Arm

Rotary vs non-rotary

Switch Coordinates

Break Resultant Force into component parts

  • horizontal
  • vertical
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6
Q

Moment Arm

A

Shortest distance between the axis of rotation & line of action of the force
Perpendicular to force’s line of action & axis of rotation

T = F∙d⊥
d⊥ = moment arm
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7
Q

Lever Arm

A

Distance between the point of force application (perpendicular component) and the axis of rotation

T = F⊥∙d
d = lever arm
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8
Q

Torque (In Humans)

A

Muscles attach at some distance away from joint center of rotation

Therefore, all muscles produce torque about the joints they cross

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9
Q

Joint Moment

A 
Muscle Contributions (internal moment)
Muscle force (tension)
Muscle lever arm

Concentric Muscle Action:
Muscle internal moment & motion same direction

Eccentric Muscle Action:
Muscle internal moment & motion opposite direction

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10
Q

Muscle Force Component -Rotary

A

Rotary Component
⊥ to bone segment
Creates internal moment
Causes motion

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11
Q

Muscle Force Component - Non Rotary

A

⊥ to rotary component, // to bone

Does not contribute to internal moment

Causes joint compression or distraction
Stabilization or Dislocation

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12
Q

Muscle Force Components

A

Joint position influences the magnitude & direction of muscle force components

Angle formed by line of action and bony segment influences magnitude of rotary and non-rotary components

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13
Q

Internal Movement created by a muscle is dependent upon:

A 
Muscle Force (F)
Lever Arm (d)
Angle of pull (θ)
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14
Q

Joint Torque - Muscle Contributions (Net Internal Moment)

A

Muscle Contributions (net internal moment)

Muscles may produce co-contraction
-Creates opposing joint torques (opposite direction)

Motion occurs in direction of net internal moment

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15
Q

What is the purpose of antagonist muscle co-contraction?

A

Control velocity of joint motion

Increase stability at joint

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16
Q

What type of contraction are the muscles producing?

A 
Quadriceps = concentric contraction
Hamstrings = eccentric contraction
17
Q

Muscle Co-Contraction- Good or Bad?

A

Adds stability and control
Increases compressive force
-Greater Co-contraction in patients with OA, ACLR/ACLD, Obesity

Contributes to stiff gait and reduced knee flexion  Disease progression

18
Q

Joint Torque Non-Muscle Contributions (External Moment)

A

Segment mass will cause a joint moment
Any external object attached or held by segment will produce a joint moment
Ground reaction forces

19
Q

Knee Adduction Moment in OA Patients

A

GRF vector is medial to the knee

Places an adduction moment on the knee and increases medial joint compression

  • Increases disease progression and severity
  • Worse in obese individuals and those with ACLR
20
Q

Equilibrium and Stability

A

Equilibrium and stability are not the same thing

21
Q

Clinical Stability

A

Response of a joint to an injurious perturbation

Ex – Valgus stress to a knee; Rolling an ankle etc.

22
Q

Biomechanical Stability

A

Ability of a loaded structure to maintain static equilibrium
Statically maintained as long as the vertical projection of the COG remains within the base of support

23
Q

Equilibrium

A

State characterized by balanced forces and torques
-No net forces and torques

Static Equilibrium
-When a body is completely motionless

24
Q

3 Conditions of Static Equilibrium

A

Sum of all horizontal forces (or force components) acting on body must be 0

Sum of all vertical forces (or force components) acting on body must be 0

Sum of all torques must be 0

∑Fx = 0
∑Fy = 0
∑T = 0
25
Q

Static Equilibrium

A

Also applies to angular analogs of Newton’s Laws
Examples
Isometric contraction
Parking brake

26
Q

Levers

A

Simple machine consisting of a relatively rigid bar that may rotate about a fulcrum

  • Bone = rigid bar
  • Joint = fulcrum

Force applied to lever moves a resistance
-Muscle = force

27
Q

3 Component of Lever

A 
-Axis of rotation (fulcrum)
Lever rotates around this axis
-Motive forces (from our muscles)
Cause rotations
-Resistive forces (from weight of limbs or objects)
Resists rotation

Three arrangements of force, resistance, and axis of rotation for a lever

28
Q

Classes of Levers

A

Classified according to the relative positions of the axis, motive force and resistive force

Acronym: A-R-M

29
Q

1st Class Lever

A

Axis between the motive force and resistive force (MAR)
e.g. = see-saw

Examples in body
Agonist/Antagonist action
Elbow extension
Plantar flexion*

30
Q

2nd Class Lever

A 
Resistance in middle (ARM)
Torque advantage usually exists for motive force
Not as versatile as 1st class lever
e.g - Push-up
What is the A, R, and M?
31
Q

3rd Class Lever

A

Motive force in middle (AMR)
Most joint complexes act as 3rd class levers
Muscle is motive force
Advantage in ROM and speed of movement but disadvantage in force
Most joint complexes are of this type

32
Q

Mechanical Advantage/Disadvantage

A

Ratio of the lever arm of the motive force to the lever arm of the resistive force for a given lever

MA = lever arm motive/ lever arm resistive

33
Q

Mechanical Disadvantage

A 
MA < 1
Mechanical disadvantage
-Motive force = Muscle force
Muscle force greater than resistive force
All 3rd class levers and some 1st class

Fmuscle&raquo_space; Fresistance
To hold a 44.5 N (10 lb) barbell you would need a muscle force of ?
1272 N
Muscles at a mechanical disadvantage
Muscle’s line of action very close to joint axis
Small lever arm

34
Q

Mechanical Advantage

A

MA > 1
Mechanical advantage
Muscle force less than resistive force
All 2nd class levers and some 1st class

A motive force can balance a larger resistance when the motive force lever arm is longer than the resistance force lever arm

Muscles do however have an advantage in movement covered
-Point further from axis must move through a greater range of motion

A motive force can move a resistance through a larger range of motion when the motive force lever arm is shorter than the resistance force lever arm

KNES 361 Exam 2 (2 decks)

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