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kin 216 > Lecture 8-10 > Flashcards

Lecture 8-10 Flashcards

1
Q

Is it possible to power a sailboat by placing a fan inside the boat?

A

no. because it violates Newton’s law of action and reaction, since it is one system, not two.

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2
Q

What is the law of inertia?

A

Law of inertia: states that every body remains in a state of constant velocity unless acted upon by an external force

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3
Q

Define inertia

A

inertia: a tendency to remain unchanged

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4
Q

what is inertia proportional to

A

Mass

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5
Q

Define momentum

A

momentum: quantity of motion, or the strength/force that something has when it is moving

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6
Q

what is the equation for momentum

A

M = mv = mass x velocity

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7
Q

what are the units for momentum

A

kgm/s

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8
Q

what is the law of conservation of momentum

A

law of conservation of momentum: the momentum in one instance should be the same as the momentum in another.

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9
Q

What is the law of momentum?

A

law of momentum: change in momentum is a result of force. Before and after contact between systems, the mv will remain the same

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10
Q

what is impulse?

A

impulse: a change in momentum

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11
Q

what is the equation for impulse

A

impulse = Ft = force x time

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12
Q

what are the units for impulse

A

Ns

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13
Q

A change in ____ produces a change in momentum

A

impulse

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14
Q

what is newton’s law of momentum mistaken for?

A

the law of acceleration. it means that force causes acceleration proportional to force, but inversely to mass

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15
Q

What are newton’s three laws?

A
  1. law of inertia
  2. law of momentum
  3. law of action and reaction
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16
Q

what is the law of action and reaction

A

law of action and reaction: states that for every force applied to a body by a second, the second applies and equal and opposite force on the first.

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17
Q

why is running on loose sand more fatiguing than running on a rubberized track?

A

As displacement increases, impact forces decrease, and so does reaction force. on a rubberized track, we receive the same ground reaction force right back. in sand, we lose our force with each step as the sand absorbs energy

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18
Q

what is mechanical work?

A

mechanical work: the amount of energy transferred to a system via force

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19
Q

what is the formula for mechanical work

A

work = Fd = force x displacement

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20
Q

what are the units for work

A

J = joules

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21
Q

If you do a bench press, where you lift up and down and have the same amount of work for each, how much work was done across the cycle?

A

none. if the work is equal, but different directions, there is net zero

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22
Q

how do we measure work

A

by measuring the weight of the object moved

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23
Q

can you have work without movement

A

no movement = no work

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24
Q

how much work is done in an isometric contraction

A

none. there is no movement, no displacement so no work

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25
what is internal work
internal work: moving the body
26
what is external work
external work: moving another system
27
is power a vector or scalar
scalar
28
what is power
power: the time rate of doing work, how quickly or slowly work is done
29
what is the formula for power
power = W / t = work / time = [force x displacement] / time = force x velocity
30
what are the units of power
Watts = W
31
what is ergometry
ergometry: a science that measures work and power
32
how would we measure power using a treadmill
force = weight of runner distance = measured distance on treadmill time = duration of run
33
how would we measure power on a bicycle ergometer
force = resistance against motion of tire distance = circumference x rpm x t time = duration of performance
34
what is energy
energy: the ability to do work
35
what kinds of energy are there
1. kinetic energy 2. potential energy
36
what is kinetic energy
kinetic energy: the capacity to do work taking motion into account
37
what kind of movement is kinetic energy
translational or rotational
38
what kind of energy involves translation or rotation
kinetic
39
what is the formula for KE?
KE = 1/2mv^2
40
what are the units for KE
joules = J
41
what is potential energy
potential energy: energy posessed by a system due to its relative position
42
what is the formula for PE
PE = ma_g h
43
what are the units for PE
Joules = J
44
when gravity is the only acting force, how does the body's mechanical energy change?
it doesnt. it remains constant
45
what is the formula for mechanical energy (C)
C = PE + Ke = ma_g h + 1/2mv^2
46
What is work in concetric shortening of muscles
positive
47
what is work in eccentric contraction
negative work
48
what is a dot scalar
dot scalar: a measure of how closely vectors align. if two vectors are going in the same direction, it is positive. negative if they are going opposite ways
49
what sign will a dot scalar have in front of it if two vectors are going in the same direction
positive
50
what sign will a dot scalar have in front of it if two vectors are going in the opposite direction
negative
51
power requires a trade off between what?
velocity and force
52
is power a vector or scalar
scalar. when we use gravity, we do NOT use the negative form of it.
53
in what calculation would we ignore the negative sign for gravity
power, since it is a scalar
54
what kind of ground reaction force can injure athletes: high or low
high
55
at the peak of vertical movement, what is KE?
zero
56
at the base of vertical movement, where height is 0, what is PE
zero
57
is it easier to push or pull a desk?
you are able to generate the same amount of force in both, but the force of friction will have different effects. ground reaction force of pushing = wt + Fy ground reaction force of pulling d = wt - Fy
58
what happens when we put a fan in a sailboat?
it turns into one system, and any work done by the fan is internal!
59
is energy scalar or vector
scalar
60
is work scalar or vector
scalar - EVEN THOUGH it can be negative, which only means that force and displacement are in opposite directions
61
is impulse scalar or vector
vector
62
is momentum scalar or vector
vector
63
what does it mean if work is negative? in what instance might it be negative?
it means that the two vectors, force and displacement, are opposite, so the dot scalar is negative. this would happen in eccentric contraction
64
what does it mean if work is positive? in what instance might it be positive?
it means that the two vectors, force and displacement, are aligned, so the dot scalar is positive. this would happen in concentric contraction
65
to do work, we require a change in _____
energy
66
Which of newton's laws relate to conservation of momentum
the first law, the law of inertia
67
Which of newton's laws do Impulse = change in M, M=mv and F=ma deal with?
second law, of momentum
68
what are the units of inertia
kg
69
What formulas are involved in Newton's first law
F= ma
70
how are newton's first and second law different
the first law relates to conservation of momentum, while the second law looks at the change in momentum
71
what is intertia proportionate to
mass
72
how many laws does newton have
three
73
What is the formula for ground reaction forces of pushing a desk?
wt + Fy
74
What is the ground reaction force of pulling the desk?
wt - Fy
75
What is wt?
weight
76
what is the formula for friction
Ff = friction coefficient x force = friction coefficient x mass x acceleration
77
what are the units for friction
newton

kin 216 (6 decks)

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