lec 20-22 Flashcards
1
Q
What are the factors responsible for non-linear relationships between muscular movements and joint movements?
A
- Bones/muscles
- bones and muscles are made of different tissues, where different tissues have different properties - Numerous muscles acting on one point
- the contribution of each muscle varies based on joint position
2
Q
what are some of the factors as to why we have irregularly accelerating movements of muscle and joint?
A
- different tissues
- varied muscle contribution
3
Q
how does the law of inertia differ between linear and angular movement
A
both state that every body persists in constant movement unless acted upon by another force. The difference is the description of the movement, as well as WHAT force changes this. In linear movement, the movement is in a straight line, and the force can be basically anything. In angular movement, the movement is rotation, and the force is torque
4
Q
With angular movement and the law of inertia, we need to know what two things?
A
mass AND axis of rotation
5
Q
define moment of inertia
A
moment of inertia: the resistance of any physical object to any change in angular state of motion
6
Q
What is the equation for moment of inertia?
A
I = mk^2
I = (mass) x (radius of gyration^2)
7
Q
what are the units of inertia
A
kgm^2
8
Q
define radius of gyration
A
radius of gyration: the linear distance between the axis of rotation to a point where the body mass is concentrated
9
Q
The moment of inertia is specific to what measure?
A
the axis of rotation
10
Q
the angular equivalent of mass is what?
A
axis of rotation
11
Q
what is the linear equivalent to axis of rotation
A
mass
12
Q
what is the principle moment of inertia
A
principle moment of inertia: the amount of inertia relative to a principle axes
13
Q
How big is inertia in the sagittal plane
A
moderate
14
Q
how big is inertia in the transverse plane
A
low
15
Q
is it harder to move in pitch, yaw, or roll?
A
roll, because it requires more torque
16
Q
is it easier to move in roll, pitch or yaw
A
yaw - there is the least amount of resistance, and the least amount of torque required
17
Q
to move, we must overcome what?
A
inertia
18
Q
what is rotational inertia affected by?
A
the distribution of mass
19
Q
moment of inertia is the angular counter part to what?
A
mass
20
Q
How is the axis of rotation different from the radius of gyration?
A
the axis of rotation is the line between the pivot point and interest point. the radius of gyration looks at the main concentration of masses
21
Q
How are mass and moment of inertia different?
A
mass is fixed, moment of inertia is not. also mass = linear and moment of inertia = angular
22
Q
What do we manipulate to alter the moment of inertia?
A
radius of gyration
23
Q
when we run, what do we do to minimize our torque?
A
we bring in our arms and legs so that less energy is required to rotate the body
24
Q
How do we change inertia?
A
Change the distribution of mass - where you grab changes the axis of rotation!
25
what does holding the heaviest part close to you do to the radius of gyration
Shrinks the radius of gyration, thus decreasing torque required
26
what does holding the heaviest portion of something away from you do to radius of gyration?
it increases the radius of gyration, thus increasing torque required
27
why is it easier to hold the heaviest portion of something close to you?
because you are shrinking the radius of gyration, meaning that there is less torque required to balance the force
28
What does it mean for the movement of an object if it has angular momentum?
it means that it is moving (rotationally)
29
if something is not moving, does it have angular momentum
no
30
what is the equation of angular momentum
H = I x w
H = mk^2w
H = moment of inertia x angular velocity
31
what are the units for angular momentum
kgm^2/s
32
in the absence of external torque, what happens to the systems movement
it remains constant
33
if a system remains in constant angular motion, what does that mean for torque
torque has to be zero
34
describe the conservation of angular momentum
the angular momentum in one instance should be the same as another instance.
35
when angular momentum is conserved, there is a tradeoff between what?
moment of inertia and angular velocity
36
what happens to the radius of gyration if you spin with your arms out, then tuck them towards you?
your radius of gyration decreases, so does the torque, and angular velocity increases
37
What action components allow a centre of mass to remain in the air in the same position?
1. compensatory movement - causes rotation
2. counter rotation - keeps the body stationary
3. initial movement
38
moment of inertia is affected by what components of the body
body and segment orientation
39
body and segment orientation affects what?
moment of inertia
40
What does it mean by local and remote term of the moment of inertia?
local = I_sw_s // examines the individual segment movement
remote = mr^2w_g // examines the entire system movement
41
how do we calculate the total angular momentum of a movement?
H_total = H_legs + H_arms + H_trunk/head
42
which has larger angular momentum, legs, arms, or head/trunk?
head and trunk! the velocity of the limbs therefore are required to stabilize the body's position
43
describe how the law of momentum is different for linear and angular movement
linear = the rate of change of momentum is proportional to the force causing it and its direction
angular = the rate of change of momentum is proportional to the torque causing it and the direction of the torque
44
what are the units for angular impulse
Nms
45
what is the formula for angular impulse
Tt = H_2-H_1
torque x time = change in angular momentum
46
with the law of acceleration, how is linear and angular movement different
linear = applied force causes acceleration in the direction it acts, inversely proportional to the body's mass
angular = applied torque causes angular acceleration in the direction of the torque, proportional, inverse to the moment of inertia
47
define equilibrium
equilibrium: a physical state, in which opposing forces equal out
48
define balance
balance: an even distribution of weight enabling someone or something to remain upright and steady
49
Of equilibrium, balance and stability, which is static, and which is dynamic
balance is static, stability is dynamic
50
define stability
stability: the capacity of an object to return to equilibrium or to its original position after it has been displaced
51
Describe how the center of gravity is a balance point
the centre of gravity is the point where all mass is equally distributed in all directions, thus it is the point where momentum is distributed equally in all directions. this means that there is net zero momentum
52
what has to be true of a system's forces for there to be equilibrium?
all of the forces have to sum to zero
53
define static equilibrium
static equilibrium: a motionless state, with no net influence acting on the system
54
define dynamic equilibrium
dynamic equilibrium: a moving state, where the system is accelerating but in control over any external influence
55
What are the formulas for dynamic equilibrium
horizontal forces = sum of F_x - ma_x
vertical forces = sum of F_y - ma_y
rotary effects = sum of T - I_alpha
56
what is stability affected by
the position of the center of gravity
57
what happens to stability as base of support increases
stability increases
58
what happens to stability if the base of support decreases
stability decreases
59
define base of support
base of support: the area beneath a system that includes every contact point on the supporting surface
60
How does stability change as the center of gravity moves to the anterior/posterior edge
stability decreases
61
what happens to stability as the center of gravity moves towards a more lateral edge of the base of support
stability decreases
62
how does the location of the centre of gravity change the ease of pushing someone over?
if the centre of gravity is higher, its easier to topple someone over
63
how does stability change as the centre of gravity moves upwards
stability decreases
64
what happens to stability if the centre of gravity lowers
stability increases
65
why is it that a higher centre of gravity decreases stability
because more torque is created in motion about the support surface
66
as mass increases, what happens to contact force, friction and stability
all of them increase
67
is friction present in the influence of stability
yes!
68
how does a pole help with balancing
it helps modulate the centre of gravity. by adding mass, it adds inertia, and increases the distribution to make you more stable. a long pole increases rotational inertia, and a curve pole lowers the centre of gravity, all to increase stability
69
define the law of inertia in linear motion terms
law of inertia (linear): the law that states every body persists in uniform straight movement (or rest), unless acted upon by another force
70
define the law of inertia in terms of angular motion
law of inertia (angular): the law that states every body persists in uniform rotation (or rest) unless acted upon by torque
71
define moment of inertia
moment of inertia: AKA rotational inertia, the resistance of any physical object to any change in its angular state of motion
72
what is mass x radius of gyration^2 equal to?
moment of inertia
73
What measures have the units of kgm^2
moment of inertia
74
how are the moment of inertia and the axis of rotation connected?
the moment of inertia is specific to a chosen axis of rotation
75
what does the principle moment of inertia examine?
the amount of inertia, relative a specific direction (to one of the principle axes of the body). it looks at how difficult it is to move the body in a particular direction
76
what rotational movements occur in each plane?
yaw pitch and roll?
77
is the moment of inertia a fixed concept
NO
78
with angular momentum, what is the tradeoff?
moment of inertia and angular velocity
79
if angular momentum stays the same, but moment of inertia increases, what happens to angular velocity
decreases
80
in angular momentum, if moment of inertia decreases what happens to angular velocity
increases
81
can we alter our orientation in space
yes! Although momentum is conserved, we can shift our axis of rotation
82
what is an example of compensatory movement
in volleyball, a compensatory movement would be kicking the legs forward to cause backwards rotation of the body
83
what is an example of counter rotation in a volleyball swing
kicking the legs back i think, for forwards rotation
84
to stabilize the body, what do we do to compensate for the larger moment of inertia of the head and trunk?
we have to increase our velocity of our arms and legs
85
What does I stand for
moment of inertia
86
define the law of momentum in linear motion terms
law of momentum (linear motion): the rate of change of momentum of a body is proportional to the force causing it and the change that takes place in the direction in which the force acts
87
define the law of momentum in angular motion terms
law of momentum (angular motion): the rate of change of angular momentum of a body is proportional to the torque causing it and the change that takes place in the direction in which the torque acts
88
what is angular impulse equal to
torque x time
89
What has to happen for there be an angular impulse
there must be a change in angular momentum
90
what is the law of acceleration in linear terms
a force applied to a body causes acceleration proportional to the force, direction of the force, and inversely proportional to mass
91
what is the law of acceleration in terms of angular motion
a torque applied to a body causes angular acceleration proportional to torque, the direction of torque, and inversely proportional to the moment of inertia
92
define the law of reaction in linear motion terms
if a body impinges on another and changes its motion, the body will undergo an equal change
93
define the law of reaction in angular motion
if a body impinges on another, and the torque changes it motion, the body will also undergo an equal change.
94
the centre of gravity is the point through which _________
the force of gravity acts
95
what happens to the centre of gravity when an individual leans to the side
the centre of gravity shifts to the side with concentrated weight
96
the vertical position of the centre of gravity is influenced by what?
the distribution of forces
97
how are the formulas for static and dynamic equilbrium different
essentially the same, but dynamic equilibrium subtracts the force by weight
98
define base of support
base of support: the area bound by the outermost regions of contact between a body and the support surface
99
how do humans control their stability?
we change our stance and body position. Staggered stance -> decreased mobility, increased stability
100
