DPT 6140 Biomechanics Quiz #3 Kinetics pt.2

Moment

Moment

The ______________ of a force is a measure of its tendency to cause a body to rotate about a specific point or axis. This is different from the tendency for a body to move, or translate, in the direction of the force.

creates angular movement!

Moment

___________= Linear force * moment arm

SI Units: (Newton.meters) or N.m

1. Linear force

oLine of action of the linear force

oPoint of application

oDirection

oAngle of application (inclination)

2. Axis

3. Some kind of distance between the linear force and axis

oDistance is the perpendicular distance between the line of the force and the axis – called moment arm

In order to create a moment we need to have 3 conditions met, what are they?

internal moment

What is a rotational force or torque provided by anatomic structures of the body (forces comes from within the body)?

Linear force, parallel

For internal moments a __________ force is occurring.

The Line of action is usually __________ to the direction of the muscle fibers

attachment, toward

For internal moment...

- Point of application is at the distal ___________ of the muscle (via the tendon) on the moving segment

- Direction moving __________ the stabilizing segment

Angle of Application (Inclination)

What is the angle between the line of action of the muscle (represented by the tendon) and the long axis of the bone onto which the tendon inserts (on the side of the joint axis.)?

In this picture is 100 degrees!

Axis

What is the

1) Instantaneous center of joint rotation (moves as joint moves)
2) Fulcrum around which angular motion occurs
3) Pivot point for angular motion

moment arm
- also called force arm, resistance arm, effort arm

What is the perpendicular distance from linear force to the axis?

moment = force

moment arm = distance from axis to linear force

_________ = force

______________ = distance from axis to linear force

MOMENT ARM

Good visual

YES. It has to be a perpendicular line to the linear force and MUST create a 90 degree angle.

- the picture demonstrates this idea

Can the moment arm line of action extended past the segment?

Segment

Moment arm

The force vector attaches on the ___________

________________ forms a 90° angle with the line of action

Blue circle = axis
Curved red arrow = angular force
Linear red arrow = linear force

General Abduction Shoulder Movement.

Blue circle = ?
Curved red arrow = ?
Linear red arrow = ?

external moment

What is a rotational force or torque provided by forces external to the body (usually ground reactive force, momentum or gravity)?

Gravity and Added resistance / free wt - are at the CoM of the segment being acted upon

NO, Added resistance / manual is at the point of contact!

What external moments have points of application that occur at the CoM?

o Gravity
o Added resistance - weights
o Added resistance - manual

Gravity

This external moment is generally vertical with direction pointing down?

in line of directed force

This picture is an example of manually added resistance, what would the line of action direction be?

Moment arm

Other names:

o Moment arm

o Resistance arm

o Effort arm

What is the line that is perpendicular (at right angle to or is at 90°) to the line of action of external force to joint axis of rotation?

opposite

- (and vice versa - internal is opposite to external)

- Ex: Lateral shoulder raises, the weight (external force is going down) and the deltoid is working to oppose this force (internal force pointing upward)

External moment direction will be ____________ to the internal moment at the same joint.

flex
(Example: Biceps are in front of joint so will flex)

If line of action of muscle is anterior to coronal axis, muscle will _______ the joint

(exception -- knee)

extend
(Example: triceps are posterior to join so will extend)

If line of action is posteriorly (behind) to the frontal axis, muscle will ________

Anterior deltoids = flex
Posterior deltoids = extend

Using this principle the anterior deltoids in front of the joint will _________ and the posterior deltoids behind the joint will __________?

abduct

If line of action of muscle passes superiorly to A/P axis, muscle will ________

adduct

If line of action of muscle passes inferiorly to sagittal or A/P axis (thick line going front/back), muscle will ________

internally or externally rotate

Subscapularis = in front of the longitudinal axis will internally rotate

Teres minor = behind the longitudinal axis will externally rotate

Location of muscle to longitudinal axis determines whether it will _________ or ___________ rotate

Red circle = axis
Red straight line = linear force
Red curved line = angular force

(The external force of the backpack pulls you back and down but the internal forces of the body pull you forward to attempt to keep you upright)

Red circle = ?
Red straight line = ?
Red curved line = ?

Red circle = axis
Red straight line = linear force
Red curved line = angular force

(External forces pulling you down toward the suitcase and internal forces trying to pull you upright)

Red circle = ?
Red straight line = ?
Red curved line = ?

B, the moment arm is greater thus the force is much greater than in picture A

In which picture will there be more force acting on the knee? A or B?

internal moment

When an external moment is acting on a joint, we usually want the body to respond by creating an opposing ________ moment

Posterior to Cervical

Anterior to Thoracic

Anterior to Knee

Anterior to Ankle

For correct posture the line of gravity is....

____________ to Cervical Vertebrae

_________ to Thoracic

___________ to Knee

____________ to Ankle

summated

Vectors can be ________________ so force composition allows for the addition of the force vectors representing two or more forces into a single resultant force

(A + B = C) but with vectors

1) Normal or typical motion

2) Poor movement patterns/poor motor control motion

When multiple internal and/or externals forces are acting at the same time composition can determine if the resultant action is: (2)

Co-linear (same line)

Co-linear or NOT co-linear?

NOT co-linear

Co-linear or NOT co-linear?

Linear system

A _________ system can be thought of as a tug of war

Parrallelogram

Opposite sides are parallel but not 90 degree angles

:), the more forces the harder it gets

This picture shows how the creation of a parallelogram can be used to find effect of non-linear forces.

Move vector down and create a polygon

Another way to find non-linear forces effect is to create a polygon (chain).

:)
- Order doesn't matter

Another example of polygon (chain) creation with 3 vectors.

:)

4 common errors when adding vectors are....

1. Magnitude not maintained
2. Direction not maintained
3. Tail-to-tip not followed
4. Resultant not correctly drawn tail-to-tip or to end of completed chain

combined

Why is vector addition important?

- To determine action of ___________ forces

:)

Example of combined forces of rotator cuff.

Is an action that has all combined forces of the deltoid working!

Anterior, posterior, and middle deltoid.

Why is manual muscle test (MMT) full deltoid muscle in shoulder abduction?

Combined forces of upper and lower pec major.

How does pectoralis major adduct?

Down to the left

Which way would the resultant be oriented?

:)

How you would draw the resultant.

The resultant, or combined, effect of these forces is directed toward the trochlear groove of the femur as a joint compression force (CF).

What would the resultant force be in this image?

perpendicular

The two component forces are _______________ to each other with the resultant in between

point of application

All 3 parts (the 2 components and the resultant) have the same point of _______________

parallel, perpendicular

One component will act __________ to lever, the other will act ______________ to the lever

Resultant force

Direction of vectors depends on direction of _________

rectangle

When lines drawn connecting tips of 2 components, a ___________ will result

oParallel component
oTangential component
oRadial component
oFx

Component Parallel to Lever has many different names.

oPerpendicular component
oNormal component
oTransverse component
oFy

Component Perpendicular to Lever has many different names.

tangential

Parallel component to the lever or segment on which it is acting will be the ____________ component with a primary function of compression or distraction

RED LINE

normal

Perpendicular component to the lever or segment on which it is acting will be the _________ component with a primary function of providing rotary movement

GREEN LINE

1) angular
2) compression in A-B, distractive force in D
3) stabilizing

The normal force, (Fy in the drawings) actually contributes to the joint _______ motion

Tangential force (Fx) creating ________ force on the joint in A – B; and a ___________ force in D

Tangential component can act as a _________ force for the joint

opposite
Tangential

Normal force acts on segment to try to produce motion _________ to that of the muscle forces (Fy)

________ may be compressive or distractive (Fx)

DO NOT
they cause compression or distraction

Tangential components do or do not cause rotation?

QLf - internal force (Quads)

FxQLf - parallel component (trying to flex knee)

FyQLf - perpendicular component (trying to extend knee)

GLf - gravity

QLf - ?

FxQLf - ?

FyQLf - ?

GLf - ?

In the picture on the left

- Clinician working harder on left

- Pt. working harder on the left (NEED much more force to resist knee extension is external force is further away, will have a much longer moment arm)

You want to resist or test knee extension. Which of the hand placements in the graphic would make it 'easier' on you?

BOTH, down more to first rotate the wheel and the push it forward.

So, is the PT pushing the wheelchair forward or downward? If both, in which direction is she pushing more?

COS

_______ is related to the adjacent side of the right triangle (typically associated with the Cartesian system x-component, although not always)

SIN

______ is related to the opposite side of the right triangle (typically associated with the Cartesian system y-component, although not always)

TAN

____ is the association between the opposite and adjacent sides

sine = opposite/hypotenuse

cosine = adjacent/hypotenuse

tangent = opposite/adjacent

SOH, CAH, TOA

•cos θ = Fx/QLf (adjacent/hypotenuse)

•sin θ = Fy/QLf (opposite/hypotenuse)

•tan θ = Fy/Fx (opposite/adjacent)

Typically used when the angle is known and one side magnitude is known:

•θ = cos-1( Fx/QLf) [adjacent/hypotenuse]

•θ = sin-1( Fy/ QLf) [opposite/hypotenuse]

•θ = tan-1(Fy/Fx) [opposite/adjacent]

When just finding the angle: