2/3: Mechanics of Motion - Vardaxis

Question 1

1 radian = _____ degrees

Answer 1

57.3

Question 2

law of sine

Answer 2

(a/ sinA) = (b/sinB) = (c/ sinC)

Question 3

law of cosine

Answer 3

a2 = b2 + c2 - 2bc cos A

Question 4

scalar vs. vector

Answer 4

scalar: magnitude only
vector: magnitude and direction

Question 5

force exerted on a body by the ground

Answer 5

ground reaction force

Question 6

resistance between 2 objects in motion or tendency

Answer 6

friction force

Question 7

internal forces

Answer 7

• muscle force
• tendon
• ligament
• intersegmental forces between bones and joint reaction forces

Question 8

define a free body diagram

Answer 8

a sketch of the outlined shape of the body or body segment, which represents it, as being isolated from its surroundings with all forces and torques that the surroundings exert on the body

Question 9

a ______ is a simple machine made with a bar free to move about a fixed point called a ________

Answer 9

lever; fulcrum

Question 10

describe the three lever types

Answer 10

• first-class lever: (see-saw, scissors, pliers)
• second-class lever: force advantage ( stapler, bottle opener, wheelbarrow, nut cracker)
• third-class lever: advantage for speed or distance (fishing rod, tweezers, tongs)

Question 11

define MA mechanical advantage

Answer 11

ratio between length of the effort arm and the length of resistance arm

MA = lever arm force / lever arm weight

Question 12

a condition in which an object is at rest if originally at rest, or has a constant velocity (linear and angular) if originally in motion

Answer 12

• law of inertia
• requires both, a balance of forces to prevent the body from translating with accelerated motion AND a balance of torques or moments to prevent the body from rotating

Question 13

inertia is the resistance a body offers to acceleration. Any attempt to accelerate the body (_______) results in an equal and opposite reaction (_______)

Answer 13

• newton II

- newton III

Question 14

for linear motion, inertia is equivalent to _____.

For rotary motion, inertia depends on ________.

Answer 14

• mass

- mass and shape (moment of inertia)

Question 15

define moment of inertia and compare high v. low

Answer 15

• resistance offered by a body to angular acceleration
• mass close to axis = low moment of inertia (easy to start and stop rotation)
• mass far from axis = high moment of inertia (hard to start and stop rotation)

Question 16

newton’s first law

Answer 16

• law of inertia
• a particle/body originally at rest or moving in a straight line with a constant velocity, will remain in this state provided it is not subjected to an unbalanced force

Question 17

newton’s second law

Answer 17

• law of acceleration
• a particle/body acted upon by an unbalanced net force experiences an acceleration that has the same direction as the force and a magnitude that is directly proportional to the force

Question 18

newton’s third law

Answer 18

• law of action-reaction

- the mutual forces of action and reaction between two particles/bodies are equal, opposite and collinear

Question 19

direct v. inverse dynamics

Answer 19

direct/forward: mechanical analysis of a system that determines movement from forces

• F known –> acceleration –> displacement
• ex: using force plate to record forces

inverse: mechanical analysis of a system that determines forces from movement
- position is known –> acceleration –> F
- ex: using video-based motion analysis

Question 20

net forces generated by bone-on-bone contact

Answer 20

• joint reaction forces

- JRF is a net force

Question 21

what sources contribute to JRF?

Answer 21

• muscle force (due to muscle activity)
• gravity related forces (mass of whole body or body segments)
• forces due to motion (inertia)
• ligamentous? controversial

Question 22

the rotational potential of a force is called …

Answer 22

• torque, joint moment or moment of force

Question 23

what are the muscles doing in gait?

Answer 23

An external GRF force: can cause motion OR can be resisted by muscle OR a combination of the above

inverse dynamics: tell us the net effect of the muscles (plus other soft tissues, ligaments, contact forces, friction and other joint surfaces)

Question 24

Notes from required Xiong paper:

Answer 24

• medial longitudinal arch of foot
• arch index obtained from footprint has correlation with all measured foot-type metrics except for the malleolar valgus index
• high arch group has significantly shorter arch lengths but larger navicular heights and higher midfoot dorsal angles compared with low arch group
• rearfoot had more loading and greater peak pressure and less midfoot load in high arch group
• reliability of all measures was higher than 0.9 expect for the subjectiv eranking
• midfoot dorsal angle is appropriate metric for characterizing foot arch, quick and easy to measure
• midfoot doral angle = 180 - calcaneal inclination angle - calcaneal-first met angle

Question 25

Notes form required Sinclair paper:

Answer 25

• traditional mechanism by which foot orthoses were believed to exert theri clinical benefits is that they serve to reduce rearfoot eversion and align the calcaneus in the vertical direction, thereby reducing the shear stress experienced by the achilles tendon
• no significant differences in GRFs
• peak ATL was significantly reduced in orthotic condition compared to without orthotic intervention
• time to ATL was longer in orthotic condition compared to without orthotic intervention
• ATL loading rate was lower in orthotic condition
• increases in dorsiflexion are associated with lengthening of the moment arm of the achilles tendon, which ultimately reduces the load experienced by the tendon itself