# Shared Flashcard Set

Biomechanics
Quiz 3
53
Physiology
11/28/2011

## Additional Physiology Flashcards

Term
 What is inertia, how do we quantify in linear motion?
Definition
 property of a body to resist a change in it's state of motion. We measure it in mass.
Term
 How do we quantify an objects resistance to a change in angular motion?
Definition
 Moment of inertia; unlike its linear counterpart, mass, the moment of inertia depends on mass AS WELL AS the distribution of mass w/ respect to an axis of rotation.
Term
 What is the formula for moment of inertia? (I), units? is moment of inertia fixed or changeable?
Definition
 I = (sum)m*r^2, units: kg*m^2it is changeable because it can be around different axes
Term
 what is angular momentum formula?
Definition
 H = I * wor = moment of Inertia * angular velocityunits: kg m^2 s-1
Term
 give examples of how (I) or moment of inertia can change in sports:
Definition
 gymnast: tuck head almost into head to reduce moment of inertia so that can accelerate and finish somersaultrunner: LOW moment of inertia when foot near buttocks, high moment of inertia when leg straightened, relative to the lower extremity relative to a transverse axis through the hip joint
Term
 During flight, what are the forces and moments acting on the diver? H?
Definition
 gravity only external force, H remains constant. Conserved during flight b/c BW vector, acting through total body center of gravity, creates no torque. This principle allows divers to mainipulate their moemnts of inertia and angular velocities.
Term
 what determines the quantity of angular momentum before a flight?
Definition
 the torque applied over time at the point of takeoff
Term
 what is the angular analog for newton's first law?second law?
Definition
 first law? conservation of momentum, so "H" stays constantsecond law? F=ma, so (sum of external)T= I*alpha
Term
 when will an external torque produce angular acceleration?
Definition
 when it is proportional and in the same direction of the torque and inversely proportion to the moment of inertia of the body
Term
 what is the formula for angular impulse-momentum and what is it derived from?
Definition
 Derived from Newton's 2nd law and it is T=(change)angular momentum / (change)in time
Term
 Why are forces exerted by muscles and loads during movement of interest?What kinds of forces do muscles produce?
Definition
 Potential of an activity to cause injury, determining task demands, loads on jointsMuscles produce eccentric forces across joints so we use joint torques
Term
 What do we need to calculate inverse dynamics? to calculate joint reaction forces and muscle moments?
Definition
 Full kinematics (filming walking), external forces, accurate anthropometric measures
Term
 In inverse dynamics, we are looking at a dynamic analysis. We then use what formula?
Definition
 (sum)Tz= I*alpha z(in static we use Fx=m*ax)
Term
 If alpha z = 0 the motion is purely _____
Definition
 linear
Term
 If ax=0 and ay=0, the motion is purely
Definition
 rotational
Term
 If all of these accelerations are -, ...
Definition
 a static case exists
Term
 Two important points about inverse dynamics:
Definition
 1. we are NOT calculating force in muscle, we are calculating a moment2. moment is NET JOINT MOMENT
Term
 Discuss the example of a bicep curl
Definition
 bicep brachii most force, triceps active to stabilize. this is example of co-contractionalso must consider passive structures like skin, other tendons
Term
 why don't we calculate force of muscles?
Definition
 because there are way too many forces and not enough equations
Term
 How do we obtain kinetic data in inverse dyanmics?
Definition
 Forces acting on system: gravity, GRF, external forces, need to be measured
Term
 What are the 3 types of body segment parameters?
Definition
 Regression equations from cadavers (problem: no blood), mathematical models (geometric solids), imaging and scanning (gamma mass; problem: exposed to radiation, MRI, DEXA)
Term
 What are assumptions when developing a link segment model? (5)
Definition
 1. segment mass is fixed2. locaiton of CM fixed during movement3. joints are frictionless hinge (or ball and socket joints)4. I is fixed at CM and is constant during movement5. length of each segment is fixed
Term
 What is the proces by reactino forces and muscle moments are calculated is called ____________
Definition
Term
 If cocontraction is taking place at a joint, what does the analysis yield?
Definition
 the net effect of agonist and antagonistic muslces, and any friction effects also all factored in as as the effective "msucle" moment
Term
 At each hinge joint what do we observe in the FBD's? (Newton's 3rd Law)
Definition
 we see an equal and opposite force acting at each hinge joint.
Term
 what are two areas of investigation for gait?
Definition
 resultant moment of force, and muscle mechanical power, are good diagnostic information
Term
 what is muscle power?
Definition
 net joint moment * joint angular velocity(+)power = concentric muscle action (i.e. flexors)(-)power: eccentric muscle action, net moment force occurs in opposite directrion as segment
Term
 Explain the moments throughout gait at the ankle when walking:
Definition
 Initially eccentric dorsiflexion at loading.Followed by net eccentric plantarflexion.Then concentric plantarflexion to push into swing phase.Then small dorsiflexion moment during initiation of swing to keep toe up.
Term
 what is mechanical work equal to?
Definition
 product of magnitude of force applied * distance object moves
Term
 what is the longer equation for work? and units?
Definition
 W= F * cos(theta) * displacement
Term
 does work reflect intensity? what is the rate at which work is being done?
Definition
 no work does not reflect intensity.power is an indicator of intensity, or rate at which work is being done
Term
 what is the formula for power? units!?
Definition
 P = W / twatts (1hp = 746 w)
Term
 Our ability to sustain a given speed depends on what?
Definition
 duration of activity
Term
 although humans are not a "powerful" machine what can we do?
Definition
 versatility in how power is applied
Term
 components of human power production, power is a combo of what?
Definition
 strength (ability to produce force) and velocity of movement= F*v
Term
 what did Lanza et. al, 2003 find? Or hypothesize?
Definition
 under isovelocity conditions, older adults slower to reach target velocity, and down shift in torque and power velocity at ankle dorsiflexor and knee extensor muscles
Term
 does the product of F and v have same units as product of T and w? can you prove this?
Definition
 P = W*t = (F*d)/t = F *vwatts, N-m/s
Term
 How can we calculate power at the elbow during a bicep curl? (aka muscle power)
Definition
 Net elbow moment, and angular velocity of the elbow joint
Term
 what does the area under a power-time curve equal?
Definition
 work done
Term
 what does positive msucle power indicate?
Definition
 concentric motion
Term
 what does negative muscle power indicate?
Definition
 eccentric action of the muscle
Term
 describe power and moment in a bicep curl:
Definition
 initial positive muscle power, positive muscle moment, concentric contraction. Then negative muscle power, still flexing but now extensors dominate
Term
 What is the study of fluid mechanics?
Definition
 study of forces that develop when an object moves through a fluid
Term
 two fluids of interest?
Definition
 water and air
Term
 two fluid forces of particular interest? and what are their definitions?
Definition
 drag: or air resistnace, opposes motion of objectlift: net force perpendicular to direction of relative motion of the fluid past the object, so perpendicular to the drag force
Term
 two types of drag: which has a greater effect?
Definition
 surface drag (friction): F to Vdepends on smoothness of surfaceform drag (pressure): F to v^2depends on cross-sectional area
Term
 in form drag (pressure), if you are going twice the speed as you were before, how much greater is the Force?
Definition
 4x greater than initially
Term
 when is surface drag referred to in sport, and form drag?
Definition
 swimming shaving, and swimming buoyancy or bicyclist, respectively
Term
 when does lift force occur?
Definition
 when object is spinning, or object not perfectly symmetrical
Term
 according to bernoulli's principle:
Definition
 pressure is inversely proportional to the velocity of air flow
Term
 how does lift force come about in an airplane wing?
Definition
 A and B air molecules move across wing at same time interval, but different distances. Thus top of wing air moves faster, resulting in lower pressure, resulting in lift force
Term
 how does the magnus effect work?
Definition
 baseball players mastered just enough spin so that they can decide which side of the ball has more or less pressure, thus the direction of the curve
Term
 what are the angular analogs of force, mass and acceleration respectively?
Definition
 torque, moment of inertia, and angular acceleration
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