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Biomechanics Exam 3 > KINETICS > Flashcards

KINETICS Flashcards

1
Q

Newton’s 1st law

A

-law of intertia
-an object at rest will remain at rest unless acted upon by an external force
-an object in constant motion will remain in constant motion unless acted upon by an outside force
-an objects momentum will remain constant

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2
Q

Newon’s 2nd law

A

-law of acceleration
-acceleration is proportional to force applied + inversely the mass of the body
-F = ma

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3
Q

force

A

the action of one body on another

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4
Q

center of pressure

A

-the theoretical point of application of a force/load transmitted through 2 contact surfaces
-weighted average of the location of all forces acting between 2 surfaces

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5
Q

linear intertia

A

mass

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6
Q

angular interia

A

moment of inertia

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7
Q

pseudoforces

A

-inertial forces such as g-forces, centrifugal force, Coriolis force, etc.
-felt as the result of another force accelerating the mass

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8
Q

intertial force

A

(-ma in [F - ma = 0])
-accounts for the tendency of a body to continue in its current state

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9
Q

net force

A

-to predict the acceleration of a body we cannot look at a single force but rather must account for all applied forces
-the sum of all applied forces is the net force which will determine the acceleration of an object from the equation Fnet - ma = 0

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10
Q

Newton’s 3rd law

A

-law of reaction
-for any action, there’s an equal + opposite reaction
-when 1 body exerts a force on a 2nd body, the 2nd body exerts a reaction force that is equal in magnitude + opposite in direction on the 1st body

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11
Q

if 2 football players collide (1 with a mass of 100kg + the other with a mass of 75kg), who feels a greater force at impact

A

-both players feel the same amount of force due to Newton’s 3rd law
-the difference is that the acceleration is going to be different for the 100kg vs the 75kg individual

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12
Q

if you jump off a cliff…describe forces

A

-you will splat but the earth will be relatively unaffected
-doesn’t mean that the force the earth felt was any different in magnitude than the force that you felt

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13
Q

2 general forms of contact forces between 2 surfaces

A

-normal force
-frictional forces

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14
Q

normal force orientation to surface

A

along axis perpendicular to surface

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15
Q

frictional forces orientation to surface

A

parallel to surface

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16
Q

ground reaction forces GRF

A

the force which the ground applies a body in contact with it

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17
Q

friction

A

force acting at an area of contact between 2 surfaces in the direction OPPOSITE of that of motion or motion tendency

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18
Q

friction ____ motion between contact surfaces

A

opposes

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19
Q

what direction is a sprinter’s GRF out of the blocks

A

anteriorly directed
-counterintuitive because sprinting out of the blocks you are pushing back + down into the ground
-the point is that the ground is pushing on YOU in the forward direction, causing you to move forward (otherwise you would move backward)

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20
Q

static friction

A

-also called maximum friction
-maximum amount of friction that can be generated between 2 static surfaces
-that means these surfaces aren’t moving relative to each other

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21
Q

object not moving = static/kinetic friction

A

static

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22
Q

object moving = static/kinetic friction

A

kinetic

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23
Q

what is the cutting movement

A

static friction
-no kinetic friction

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24
Q

when do you have kinetic friction

A

when you are sliding

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25
Q

kinetic friction

A

-constant magnitude friction generated between 2 surfaces in contact during motion
-these surfaces are moving relative to each other

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26
Q

which force is almost ALWAYS less: kinetic friction or static friction

A

kinetic friction

27
Q

based on what does the coefficient of friction change

A

depending on whether the object is stationary or moving

28
Q

which coefficient of friction will always be less: kinetic or static

A

kinetic

29
Q

how are forces measured in lab

A

force plates

30
Q

6 main outcome variables of force plates in lab

A

Fx: X component of GRF
Fy: Y component of GRF
Fz: Z component of GRF
Mz: free moment about Z-axis
Cx: X location of COP
Cy: Y location of COP

31
Q

strain gauges

A

-measure force applications
-mounted to all 4 corners of a force plate
-you can resolve where the COP is if you have this spatial distribution of what forces are being applied to the force plate

32
Q

free moment

A

-the twisting effect you may apply to a force plate about the z-axis
-force plate measures this twisting effect

33
Q

any time you apply a force that is off axis of its COM, what happens

A

you cause rotational or angular acceleration alongside linear acceleration

34
Q

if you have another force that is equal + opposite + applied at a different point, you can only have what type of acceleration

A

rotational (angular)

-forces cancel out in the x direction because their line of rotation is removed but parallel
-only causes turning effect on that object
-that is what a free moment is

35
Q

vicon

A

type of motion capture software

36
Q

what should vertical GRF look like for quiet standing

A

static (basically motionless)
-around BW
-force plate is like a scale in this case
-fluctuations corresponse to noise in the signal, small postural adjustments you may make while quietly standing

37
Q

what should horizontal GRF look like for quiet standing

A

again, static (small postural adjustments)
-BELOW BW, horizontal GRF = 0
-this is a frictional force, so no potential for relative motion when just standing
-no external applied force other than gravity SO you should not have a frictional force if quietly standing

38
Q

what should vertical GRF look like for gait

A

-in single leg support we have fluctuations of GRF above + below BW
-above BW = upward acceleration of COM
-below BW = downward acceleration of COM

39
Q

what should horizontal GRF look like for gait

A

significantly smaller than vertical GRF because any nonzero force causes acceleration

40
Q

what part of shoe is typically worn down

A

lateral side of heel

41
Q

in the absence of outside force, what is conserved

A

momentum

42
Q

elastic collision

A

-conservation of energy + momentum
-2 balls colide + bounce off each other perfectly elastically

43
Q

inelastic collision

A

-energy + momentum are conserved
-2 balls collide + continue as 1 combined mass

44
Q

real world collisions where objects don’t stick together tend to be elastic/inelastic

A

partly elastic, partily inelastic

45
Q

coefficient of restitution

A

indicative way of denoting how elastic/inelastic a collision is

46
Q

impulse can give us some idea about what

A

likelihood of injury

47
Q

when right leg is braking, is horizontal (anterior-posterior) GRF negative/positive

A

negative- meaning posterior

48
Q

when right leg is in propulsion, is horizontal (anterior-posterior) GRF negative/positive

A

positive- meaning anterior

49
Q

anterior = propulsion = positive horizontal GRF

A
50
Q

posterior = braking = negative horizontal GRF

A
51
Q

consider a continuous gradual increase of an applied horizontal force to this sled. once the applied horizontal force FA on a sled shown overcomes static friction, the dynamic friction will increase linearly as the applied force continues to increase

A

false

52
Q

during quiet standing the horizontal ground reaction force is approximately zero

A

true

53
Q

if 2 hockey players, one with a mass of 80kg and a velocity of 3 m/s and the other with a mass of 90kg and velocity of -2.8 m/s collide elastically (bounce off). what is true of their respective accelerations during the collision?

A

the smaller player will have greater acceleration

54
Q

2 hockey players, one with a mass of 80kg and a velocity of 3 m/s and the other with a mass of 90kg and velocity of -2.8 m/s collide. what is true of the forces felt by the hockey players during the collision?

A

they both feel the same magnitude of force

55
Q

if the magnitude of a person’s ground reaction force is less than their mass*9.81 what is happening?

A

COM has a downward acceleration

56
Q

during countermovement phase (descent into the loaded position) of the countermovement jump, the vertical ground reaction force does which of the following?

-first rises above BW then drops below BW
-first drops below BW then rises above BW
-it drops below bodyweight and stay below body weight until the COM reaches its lowest position
-it rises above bodyweight and stay below body weight until the COM reaches its lowest position

A

first drops below BW then rises above BW

57
Q

true/false: during the launch and landing of a countermovement jump, the maximum vertical ground reaction force measured will always be the same

A

false

58
Q

to make a cutting movement in soccer effectively and efficiently it is best to have ________________ between your foot and the ground

-kinetic friction
-no friction
-static friction

A

static friction

59
Q

true/false: an increase in the mass of a person will increase the maximum static friction between the person’s feet and the ground

A

true

60
Q

the maximum vertical ground reaction force occurs during what phase of the countermovement jump?

A

landing

61
Q

sliding = kinetic/static

A

kinetic

62
Q

cutting = static/kinetic

A

static

63
Q

running is static/kinetic

A

static

Biomechanics Exam 3 (5 decks)

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