Term
| What is inertia, how do we quantify in linear motion? |
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Definition
| property of a body to resist a change in it's state of motion. We measure it in mass. |
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Term
| How do we quantify an objects resistance to a change in angular motion? |
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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. |
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Term
| What is the formula for moment of inertia? (I), units? is moment of inertia fixed or changeable? |
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Definition
I = (sum)m*r^2,
units: kg*m^2
it is changeable because it can be around different axes |
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Term
| what is angular momentum formula? |
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Definition
H = I * w
or = moment of Inertia * angular velocity
units: kg m^2 s-1 |
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Term
| give examples of how (I) or moment of inertia can change in sports: |
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Definition
gymnast: tuck head almost into head to reduce moment of inertia so that can accelerate and finish somersault
runner: 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 |
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Term
| During flight, what are the forces and moments acting on the diver? H? |
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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. |
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Term
| what determines the quantity of angular momentum before a flight? |
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Definition
| the torque applied over time at the point of takeoff |
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Term
what is the angular analog for newton's first law?
second law? |
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Definition
first law? conservation of momentum, so "H" stays constant
second law? F=ma, so (sum of external)T= I*alpha |
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Term
| when will an external torque produce angular acceleration? |
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Definition
| when it is proportional and in the same direction of the torque and inversely proportion to the moment of inertia of the body |
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Term
| what is the formula for angular impulse-momentum and what is it derived from? |
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Definition
| Derived from Newton's 2nd law and it is T=(change)angular momentum / (change)in time |
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Term
Why are forces exerted by muscles and loads during movement of interest?
What kinds of forces do muscles produce? |
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Definition
Potential of an activity to cause injury, determining task demands, loads on joints
Muscles produce eccentric forces across joints so we use joint torques |
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Term
| What do we need to calculate inverse dynamics? to calculate joint reaction forces and muscle moments? |
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Definition
| Full kinematics (filming walking), external forces, accurate anthropometric measures |
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Term
| In inverse dynamics, we are looking at a dynamic analysis. We then use what formula? |
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Definition
(sum)Tz= I*alpha z
(in static we use Fx=m*ax) |
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Term
| If alpha z = 0 the motion is purely _____ |
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Definition
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Term
| If ax=0 and ay=0, the motion is purely |
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Definition
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Term
| If all of these accelerations are -, ... |
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Definition
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Term
| Two important points about inverse dynamics: |
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Definition
1. we are NOT calculating force in muscle, we are calculating a moment
2. moment is NET JOINT MOMENT |
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Term
| Discuss the example of a bicep curl |
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Definition
bicep brachii most force, triceps active to stabilize. this is example of co-contraction
also must consider passive structures like skin, other tendons |
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Term
| why don't we calculate force of muscles? |
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Definition
| because there are way too many forces and not enough equations |
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Term
| How do we obtain kinetic data in inverse dyanmics? |
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Definition
| Forces acting on system: gravity, GRF, external forces, need to be measured |
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Term
| What are the 3 types of body segment parameters? |
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Definition
| Regression equations from cadavers (problem: no blood), mathematical models (geometric solids), imaging and scanning (gamma mass; problem: exposed to radiation, MRI, DEXA) |
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Term
| What are assumptions when developing a link segment model? (5) |
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Definition
1. segment mass is fixed
2. locaiton of CM fixed during movement
3. joints are frictionless hinge (or ball and socket joints)
4. I is fixed at CM and is constant during movement
5. length of each segment is fixed |
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Term
| What is the proces by reactino forces and muscle moments are calculated is called ____________ |
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Definition
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Term
| If cocontraction is taking place at a joint, what does the analysis yield? |
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Definition
| the net effect of agonist and antagonistic muslces, and any friction effects also all factored in as as the effective "msucle" moment |
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Term
| At each hinge joint what do we observe in the FBD's? (Newton's 3rd Law) |
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Definition
| we see an equal and opposite force acting at each hinge joint. |
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Term
| what are two areas of investigation for gait? |
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Definition
| resultant moment of force, and muscle mechanical power, are good diagnostic information |
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Term
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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 |
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Term
| Explain the moments throughout gait at the ankle when walking: |
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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. |
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Term
| what is mechanical work equal to? |
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Definition
| product of magnitude of force applied * distance object moves |
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Term
| what is the longer equation for work? and units? |
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Definition
| W= F * cos(theta) * displacement |
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Term
| does work reflect intensity? what is the rate at which work is being done? |
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Definition
no work does not reflect intensity.
power is an indicator of intensity, or rate at which work is being done |
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Term
| what is the formula for power? units!? |
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Definition
P = W / t
watts (1hp = 746 w) |
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Term
| Our ability to sustain a given speed depends on what? |
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Definition
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Term
| although humans are not a "powerful" machine what can we do? |
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Definition
| versatility in how power is applied |
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Term
| components of human power production, power is a combo of what? |
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Definition
strength (ability to produce force) and velocity of movement
= F*v |
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Term
| what did Lanza et. al, 2003 find? Or hypothesize? |
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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 |
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Term
| does the product of F and v have same units as product of T and w? can you prove this? |
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Definition
P = W*t = (F*d)/t = F *v
watts, N-m/s |
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Term
| How can we calculate power at the elbow during a bicep curl? (aka muscle power) |
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Definition
| Net elbow moment, and angular velocity of the elbow joint |
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Term
| what does the area under a power-time curve equal? |
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Definition
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Term
| what does positive msucle power indicate? |
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Definition
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Term
| what does negative muscle power indicate? |
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Definition
| eccentric action of the muscle |
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Term
| describe power and moment in a bicep curl: |
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Definition
| initial positive muscle power, positive muscle moment, concentric contraction. Then negative muscle power, still flexing but now extensors dominate |
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Term
| What is the study of fluid mechanics? |
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Definition
| study of forces that develop when an object moves through a fluid |
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Term
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Definition
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Term
| two fluid forces of particular interest? and what are their definitions? |
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Definition
drag: or air resistnace, opposes motion of object
lift: net force perpendicular to direction of relative motion of the fluid past the object, so perpendicular to the drag force |
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Term
| two types of drag: which has a greater effect? |
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Definition
surface drag (friction): F to V
depends on smoothness of surface
form drag (pressure): F to v^2
depends on cross-sectional area |
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Term
| in form drag (pressure), if you are going twice the speed as you were before, how much greater is the Force? |
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Definition
| 4x greater than initially |
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Term
| when is surface drag referred to in sport, and form drag? |
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Definition
| swimming shaving, and swimming buoyancy or bicyclist, respectively |
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Term
| when does lift force occur? |
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Definition
| when object is spinning, or object not perfectly symmetrical |
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Term
| according to bernoulli's principle: |
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Definition
| pressure is inversely proportional to the velocity of air flow |
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Term
| how does lift force come about in an airplane wing? |
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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 |
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Term
| how does the magnus effect work? |
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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 |
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Term
| what are the angular analogs of force, mass and acceleration respectively? |
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Definition
| torque, moment of inertia, and angular acceleration |
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