DPT 6140 Biomechanics Quiz #2

forces

forces

Kinetics examines the ________ that allow maintenance of equilibrium or balance, and that cause or influence movement

Kinematics

HOW movement occurs?

Kinetics

WHY movement occurs?

Force
- is a vector

What is action of one body on another?

Linear Force
- units = Newtons or N

Term:

What is?

- “push” or “pull” in a straight line

- Creates linear or translatory action

- Represented by a straight arrow

Rotational/Angular Forces
- Units = N.m or Newton Meters

Term:
What is it?

- Generally known by the terms 'moment' or 'torque'
- represented by a curved arrow
- Still indicates direction
- Still can be added if there is more than one

distance

- Need to push farther from the axis to create an angular force

(Think about pushing at the scapula vs. the spine to turn the body)

If a linear force is applied at a __________ from an axis, then there exists a potential for rotation or angular movement around that axis

1.Linear force

2.Axis

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

By definition, we need to have 3 conditions to create a moment!

What are they?

moment arm

Term:
What is this?

Distance is the perpendicular distance between the line of the force and the axis

RED LINE!

Moment

__________ = Linear force * moment arm
SI Units: (Newton.meters) or N.m

Purple: Linear force

Light blue: Axis

Green lines: Moment arm

What do the Purple arrows represent?

What does the light blue circle represent?

What do the green lines represent?

External forces

What are Force(s) that arises from outside the body, environmental?

Internal forces

What are Force(s) that arises from inside the body

Red = external

light blue = internal

What does the red arrow represent?

What does the light blues arrow represent?

tension

What types of force?

compression

What types of force?

shear force

What types of force?

bending force

What types of force?

torsion

What types of force?

Tension

Term:
Equal and opposite loads extending outward from surface of structure; applied in parallel to long axis of object

Tension
- indicate a force that is perpendicular to a joint surface, is directed away from that joint surface and allows for separation of the joint surfaces

Joint Distraction is an example of what type of force?

Compression / Compressive

Term:
Equal and opposite loads are applied toward the surface of a structure

Joint Compression/Compressive Forces

Term:
Applying perpendicular forces to joint surfaces directed toward the surface in attempt to bring the surfaces together

- it is the opposite of joint distraction

Shearing force

TERM:
is any force (or component of a force) that has an action line parallel to contacting surfaces (or tangential to curved surfaces) that creates or limits movement between surfaces

- Two parallel forces applied in opposite directions - not in line with each other

Shearing force

What is this an example of?

tension and compression

Bending forces includes both: __________ and __________

Torsion

What is this an example of?

combined loading

What is the simultaneous action of two or more types of forces?

synonymous

Angular moment and rotation are _________________.

linear force

If there is angular moment occurring that means that has to be a ___________ force.

Mass

What is the amount of matter of which a body is composed?

CoM, center of mass

What is the point at which a body's mass is concentrated in equilibrium (evenly distributed)?

CoM, Center of Mass

What is the point where acceleration of gravity acts on the body (whole body and segment)?

WILL NOT CHANGE

For single object or rigid body --> CoM will or will not change regardless of orientation?

WILL NOT CHANGE

For segments --> CoM will or will not change location as the mass of a given segment is fixed for an individual?

move

For linked systems --> as the masses of the links move, orientation of masses also changes and the CoM for the entire system will ______?

center of system

When external mass like a heavy backpack is removed, the CoM will move again move towards ____________?

CoM will move to the right and down

Which direction(s) the full body CoM would move?

•Holding a heavy suitcase in the right hand (below waist level) at the side of the body

CoM will move up

Which direction(s) the full body CoM would move?

•Bilateral transfemoral amputation

CoM will move up

Which direction(s) the full body CoM would move?

•Carrying a child on the shoulders (child’s legs around neck/feet on chest)

gravity

A force (typically denoted ‘G’) on a mass pulled by earth’s mass causing object to accelerate toward the earth?

9.81 m/s2

Objects accelerate at g=_____ m/s2 toward earth

Weight
- type of force

________ = mass * g

line of action

The line along which a force acts?

By Convention - it is located at the segment and/or external object’s CoM

For external forces the point of application starts where?

By Convention - it is located at the attachment site for the muscle on the bone that is being acted upon (proximal/distal insertion sites of the muscle)

For internal forces the point of application starts where?

Line of gravity (LoG)

What is imaginary vertical line either from or through CoM to surface?

- Typically represents affect of gravity on the body

Base of support (BoS)

What is defined by contact of system to ground?

Ground Reaction Force (GRF)

What force is generated by contact with the ground in turn results with the ground reacting or 'pushing back'?

angular force

___________ force is also called a moment or torque

linear forces

'translatory' or 'translation' are also used to describe _________ forces

stability

TERM:

1) Can refer to the ability to maintain or return to a steady state in presence of perturbations

AND

2) Degree to which one can stand still or move without falling (full body)

1) LoG within base of support

2) The closer to the center of the base of support that the LoG falls, the more stable

3) Larger the base of support, more stable

4) The lower the CoM is to the base of support, more stable

Conditions for Mechanical Stability:

1) LoG falls _________ base of support

2) The ________ to the center of the base of support that the LoG falls, the more stable

3) ________ the base of support, more stable

4) The _______ the CoM is to the base of support, more stable

Balance

TERM:

1) Can refer to the capability of a system to move without falling – control is lost and the “fall” is to the ground or supporting surface

AND

2) The integration of systems whose ultimate goal is to maintain static or dynamic stability

Balance, Stability

___________ is your ability to control your body without movement against gravity.

___________ is your ability to control your body during movement.

decreases

Standing with single leg is harder because your base of support _______________ and every time your center of mass moves outside base of support, your balance will be challenged.

1) LoG falls outside of the base of support

2) Controlled mobility --> alternates with LoG falling within and out of the BOS

With mobility...

1) LoG falls _________ of the base of support

2) Controlled mobility --> alternates with LoG falling within and out of the ______

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!

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 ___________ of the muscle (via the tendon) on the moving segment

- Direction is __________ 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.)?

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 ARM

Good visual

vector

Line of action

Moment arm

The force __________ attaches on the segment

_____________________ can be extended past the segment

________________ forms a 90° angle with the line of action

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:
oMoment arm
oResistance arm
oEffort 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?

flex

If line of action of muscle passes anterior to coronal axis, muscle will _______ the joint (exception -- knee)

extend

If line of action passes posteriorly to the frontal axis, muscle 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 ________

internal moment

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

e. A and B
Best response as both A and B are correct

Which of the following may a line of action represent?

a. Line along which an internal force may act
b. Line along which an external force may act
c. The perpendicular distance that is the internal moment arm
d. The perpendicular distance that is the external moment arm
e. A and B
f. C and D
g. A, B, C and D

d. all the above

To create an angular force/moment/torque, which of the following do you need to have?

a. An axis of rotation
b. A linear force
c. Distance between the linear force and axis
d. all the above

True

Internal forces and moments are usually in response to (or counters) an external stimuli or force or moment.

(T or F)

False, A tensile force is being applied at the ankle joint where the right hand is exerting an upward force and the left hand is exerting a downward force. Hence it is a joint distraction force.

In the figure shown below, if the right hand is pulling up and the left hand is pulling down, the red arrow is indicating joint compression force at the ankle joint.
(T or F)

B, because moment arm is perpendicular distance from an axis to the line of action of force.

In the figure below, which of the following situations has the longest moment arm for the knee?
A, B, or C?

:)

Good picture to demonstrate answer to previous question.

True, The Center of Mass of a group of segments can be manipulated or changed by orienting the segments in different positions.

The center of mass of a segment is fixed but the center of mass of a system consisting of several segments can be manipulated based on the orientation of the individual segments.
(T or F)

False, Base of support is larger in double support phase as both the feet are on the ground.

Walking with increased double support phase (both feet on ground) and decreased single support phase (only one foot on ground in stance phase and other foot in swing phase) is an indicator of more cautious gait because the base of support in double support phase is smaller than the base of support in single support phase.
(T or F)

False.

Center of mass and center of pressure refer to different points. Center of mass is where the whole mass of the body can be assumed to be concentrated. Center of pressure is the point of application of the ground reaction force. Center of mass is a point in 3-dimensional space (x,y,z). Center of pressure is often referred to in 2-dimensional space (x,y).

The terms Center of mass and Center of pressure refer to the same point in space.
(T or F)

c. The CoM is closer to the ground while sitting in the couch thereby increasing stability but making hard for the mobility to occur

It will be harder for your patient to get up from a couch while sitting all the way to the back compared to getting up from a regular chair because:

a. The CoM is higher up from the ground while sitting on the couch thereby decreasing both stability and mobility to occur
b. The CoM position has nothing to do with this
c. The CoM is closer to the ground while sitting in the couch thereby increasing stability but making hard for the mobility to occur

True

Point of application of gravity force on a segment/body is always from the center of mass of that segment/body and does not change with the orientation of the segment/body.
(T or F)

False, Ground reaction force is 3-dimensional and is the reaction force in response to both gravity and muscle actions

Ground reaction force is only representative of the reaction force from the ground only in the vertical direction in response to gravitational force which is always in vertical direction.
(T of F)