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Kinesiology > Describing the System [1] > Flashcards

Describing the System [1] Flashcards

1
Q

what is the law of inertia?

A

a body stays in its state of rest OR in motion, unless it is compelled to change that state by forces impressed upon it
- a body in motion stays in motion ect..

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2
Q

What is the law of acceleration?

A

change in motion is directly proportional to the magnitude of the applied force
F = MA

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3
Q

What is acceleration?

A

Observed change in motion
- even deceleration falls under this category

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4
Q

What is the law of action-reaction?

A

To every action there is always an opposed and equal reaction
- these forces occur in pairs
(Think of a race car; gravity pulls down, road pushes up; & engine propels forwards, drag/friction pulls backwards)

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5
Q

What are JRF’s?

A

Joint Reaction Forces: they keep our joints stable while our muscles move
- ex: shoulder abduction; humeral head stays in socket while deltoid muscles move

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6
Q

What is considered a force?

A

Something with the capability to cause a change in motion of a system
- ex: push or pull

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7
Q

What are the different properties of a force?

A
  • magnitude: size of applied force
  • orientation: alignmnet of the vector in relation to cardinal directions
  • direction: the way the force is applied
  • line of action: imaginary line extending indefinitely along the vector through tip and tail
  • point of application: point at which the system receives the applied force
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8
Q

What types of forces are there?

A
  1. Non-contact (field) forces
  2. Contact forces
  3. External and Internal forces
  4. Action and reaction forces
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9
Q

Explain non-contact (field) forces

A

Law of universal gravitation explains the ineraction of objects even when not in contact with each other
- ex: magnets
- field: any object possessing mass creates an invisible field of influence stretching throughout the space

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10
Q

What type of force is the electromagnetic force?

A

Non-contact field force
This force it is between electric charges
- gravitational forces exists between bodies of mass
- our body expeireces both electromagnetic and gravitational forces

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11
Q

What are contact forces?

A

the result of phsyical contact between 2 bodies

ex: hitting a ball with a bat

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12
Q

What are external forces?

A

those that intercat with the system from the outside
- change the motion of the system

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13
Q

What are internal forces?

A

they act within the defined system
- they change the shape of the system

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14
Q

What is an action force?

A

The initially applied force

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15
Q

What is a reaction force?

A

the simultaneous equal counterforce acting in the opposite direction to the action force
- locomotion

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16
Q

How does Newton’s 3rd law relate to action & reaction forces?

A

Essentially the force the body places on the earth, earth places back on the body
- intenal forces on the system are the muscles
- the exertrnal forces are the equal and opposite force applied by the earth; which creates motion

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17
Q

What is ground reaction force?

A

keeps us stable as we walk
- on sand GRF is not quite the same and can’t give us back the force we put on it

18
Q

How does gravity work in relation to weight?

A

Gravity pulls on an objects mass with a ceratin amount of force (it gives us weight in a downward direction)
- Weight: the measure of the force with which gravity pulls upon an objects mass
-

weight changes as we get closer to and darther from the center of the ea

19
Q

What are the 2 types of resultant forces?

A
  • Centripetal force: any force that causes a system to exhibit circular motion (center seeking)
  • Centrifugal force: the force that is equal to and opposite the centripetal force (center fleeing/fugitive)
20
Q

What is friction?

A

A force that resists the sliding of 2 objects in contact
- exists when 2 objects in contact have the potential to slide across each other
- vectors that represent frinction force has a direction that is opposite of the potential sliding direction and parallel to the 2 surafces in contact

friction is resistance to sliding

21
Q

What is static friction?

A

occurs when 2 contacting surfaces are not sliding/moving relative to each other BUT do posses the potential for movement
- to move a box the static friction < applied force
- thus once it moves it goes from static friction to kinectic friction

desk has static friction against the floot

22
Q

What is kinetic friction?

A

friction in which 2 surfaces are already sliding relative to each other
- easier to move a box with kinetic frinction than static friction bc coefficient is lower

23
Q

What is rolling friction?

A

occurs whenever one surface is rolling over another but not sliding
- coefficient of rolling friction is < than static and kinetic which is why this is the easiest to do

24
Q

How does pressure interact with force?

A

Pressure is the magnitude of applied force acting over a certain area
- Pressure = Force/Area

Ex: laying on a bed of nails manipulates pressure to avoid puncture
- weight of a person = applied force (F)
- area over which it is applied = total area of the tips of the nails (A)

25
Q

What is stress?

A

The external force acting to deform a material
- (similar to pressure it is calculated as an external force)

26
Q

What is strain?

A

The resulting magnitude of deformation as a result of the applied stress
- the percentage of change in length is due to an applied stress
- Strain = Change in length/initial length

Its all about HOW it deforms

27
Q

Describe Poisson’s Ratio

A

tendency of a metrial to exhibit transverse strain simultaneously with an axial strain
[Basically it narrows as it lengthens]
- poisson’s ration has values between 0.00 (very elastic) and 0.50 (perfectly incompressible)

28
Q

Describe the stress strain curve and draw and label it

A
  • A= high strength & low ductility not malleable (ex: bone; once it deforms its done)
  • B = medium strength & medium ductility (ex: ligaments and tendons; they can deform and still recover)
  • C = low strength & high ductility (ex: cartilage; it is easy to deform and it handles it easily)
29
Q

What are the stress/strain values

A
  • strength= max stress or strain a material can withstand without permanent deformation
  • ductility: =force p/unit area required to deform a material; represented by steepness of slope
  • toughness: = total energy required to cuase material failure
30
Q

What is the elastic region?

A

the linear portion of the stress/strain curve
- the material will return to its original shape if the tensile stress is removed within this range

31
Q

What is the yield point in the stress/strain curve?

A

the point at which the applied stress can lead to permanent deformation

32
Q

What is the plastic region of the stress/strain curve?

A

non-linear response of the material after the yield point
- some degree of deformation will perist after removal of stress
- occurs after yield point and before ultimate strength (which is deformation without repair)

33
Q

What is tension stress?

A

two forces applied to a system in opposite directions, away from each other

34
Q

What is compression stress?

A

result of 2 forces being applied to the system in opposite directions, towards each other

35
Q

What is Shear Stress?

A

2 parallel forces that tend to simultaneously displace one part of a system in a direction opposite another part of the system

36
Q

What is bending stress?

A

2 off-axis forces are applied such that tension stress is cuased on one side of the system and compression stress occurs on the other side
- combines tension and compression stress

37
Q

What is torsion stress?

A

two forces being applied in such a way that part of the sytem is rotated around its longitudinal axis in a direction opposite roattion of another part of the system

twisting motion

38
Q

What is the coefficicnet of restitution?

A

Materials vary in their ability to reform after deformation
- the coefficient is the paramter observed after reformation that indicates the aility of an object to return to its original shape after deformation
- measured by rebound
- E= sq root of (Height of drop divided by Height of rebound)

ranges from 0.00 (inelastic) - 1.00 (perfectly elastic)

39
Q

What is Viscoelasticity?

A

A material whose deformation is affected by both the rate of loading and the length of time that it is subjected to a constant load (starts to involve fluids)
- think of the spine

40
Q

What is stress relaxation?

A

the corresonding eventual decrease in stress that will occur as fluid is no longer exuded/compressed

this can occur while we sleep

Kinesiology (16 decks)

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