Quiz 2 Flashcards
1
Q
What is the equation for force? what is the unit?
A
f = m x a (N)
2
Q
What is the equation for inverse dynamics? what is the unit?
A
a = f/m (m/s2)
3
Q
What is the equation for Momentum? what is the unit?
A
p = m x v (kg.m/s)
4
Q
What is the equation for Impulse? what is the unit?
A
J = ∑F x Δt (N.s)
5
Q
What does the impulse momentum theorem state?
A
The impulse-momentum theorem states that the change in momentum of an object equals the impulse applied to it.
∑FΔt = m(vf-vi)
6
Q
Do the resultant forces have x and y components? what is the formula?
A
yes,
Rx = ƩFx = max
Ry = ƩFy = may
7
Q
What is the use of inverse dynamics?
A
used to determine the resultant force acting on an object if the object’s acceleration is known
8
Q
How is motion captured in inverse dynamics?
A
motion is captured through motion capture systems (cinematography, vicon, optitrak)
9
Q
What is the formula for average acceleration?
A
a = vf – vi/ t
10
Q
What two variables is impulse the product of?
A
force and time
11
Q
How can impulse be calculated?
A
Can be calculated as the area under a
force-time curve
12
Q
What is the unit for impulse? is it a vector or scalar quantity?
A
Units = N*s
Vector Quantity
13
Q
What is the definition of momentum?
A
Describes body’s persistence to stay in motion
14
Q
What are the 2 things that linear momentum depends on?
A
Linear Momentum depends on the quantity of:
*Mass
*Velocity
15
Q
What is the unit of momentum? is it a vector or scalar quantity?
A
Units = kg*m/s
Vector Quantity
16
Q
What is the impulse momentum relationship? where is the relationship derived from?
A
The impulse of a force applied to an object causes a change in momentum of the object
Relationship is derived from Newton’s 2nd Law: ∑F = m*a
*Given that: a = Δv/Δt
*Then: ∑F = m * Δv/Δt
Rearranged: ∑FΔt = m * Δv
OR
∑FΔt = m(vf-vi)
17
Q
How do positive and negative net forces affect velocity?
A
(Applying a force to a body for a duration will change the velocity of the body)
*Positive net force = increased velocity
*Negative net force = decreased velocity
18
Q
What is the impulse-momentum equation? Which side is which?
A
∑FΔt = m(vf-vi)
left side = impulse
right side = momentum
19
Q
What are three sports examples of when we want to increase momentum?
A
*Throw events
*Run events
*Jump events
20
Q
What are three sports examples of when we want to decrease momentum?
A
*Jump landing
*Catching a ball
*Pole vault landing
21
Q
What must be done to give an object momentum?
A
To give an object momentum, impulse must be applied
22
Q
How fast can momentum changes occur?
A
Change in momentum can occur:
* Slowly (marathon)
* Quickly (100m sprint)
23
Q
What are 3 ways to achieve more momentum?
A
Achieve more momentum by:
* Increasing force
* Increasing time
* Increase pulses
24
Q
What are 2 ways to maximize momentum change? give an example of each?
A
Maximize momentum change in two ways:
*Small force applied over long time
ex.throwing and pushing activities (ie. windup – baseball pitching)
*Large force applied over short time
ex.ball and implement collisions (ie. golf, tennis)
25
which directions do force plates measure?
Force plates measure force applied in 3 directions (x,y,z)
26
What two energies can rigid bodies possess? What do they total up to?
Rigid bodies can possess two types of energy:
Potential Energy (PE) & Kinetic Energy (KE)
the Potential and Kinetic energies make up the total Mechanical Energy (ME) of a rigid body
That is.... ME = PE + KE
27
What is the definition of gravitational potential energy? what is the formula?
Gravitational Potential Energy is due to the gravitational attraction of the Earth and is dependent upon the height of the center of gravity of the body above a reference.
PE = m.g.y
PE is the potential energy of the rigid body
m is the mass of the body
g is the gravitational force (9.81 m/s2)
y is the height of the object above the reference (time)
28
What is the second type of potential energy? where is it found? how does it occur?
A second type of potential energy exists: Elastic Potential Energy
It is present in non-rigid, or deformable bodies (springs, ligaments, bones and muscles).
Non-rigid bodies are capable of storing, then releasing mechanical energy depending on their physical properties and the amount of deformation they experience.
*The more a spring is stretched or depressed, the more mechanical energy it stores.
29
What causes elastic potential energy? give two examples
*Due to stored energy in an object
–Ex: Muscles, tendons, ligaments
*energy storage depends on their composition i.e. collagen to elastin fibres
–Ex. Diving Board
*Depress the board = stored energy
*Recoil of board = returns energy
30
What is the definition of kinetic energy? what are the two types?
Kinetic energy is the energy of the object in motion (½ mv2 )
Kinetic energy includes both a translational form and a rotational form due to the motion of a body.
31
What is the difference between translational and rotational kinetic energy? Which are we more concerned with?
the amount of mechanical energy that the body has due to its translational (linear / curvilinear) motion
Vs.
the amount of mechanical energy that the body has due to its rotational motion
We are most concerned with translational kinetic energy because usually in humans, the greatest amount of mechanical energy is in the form of translational kinetic energy
32
What are the formulas for translational and rotational kinetic energy?
KE translational:
½ mv2 = ½ mvx2 + ½ mvy2
KE rotational:
½ Icgω2
33
What is total mechanical energy? what is it measured in?
Total mechanical energy (ME) is the sum of the body’s potential and kinetic energies.
Measured in Joules (J)
34
What is the formula for total mechanical energy?
ME = PE + KEtranslational + KErotational
Or
ME = mgy + ½ mvx2 + ½ mvy2 + ½ Icgω2
35
What type of energy does a vaulter have at different stages of the skill?
1. Prep Phase: running down the track = (blank)
2. Plant Phase: plant the pole and rise on the pole to the peak height = (blank)
3. Top of jump = (blank)
4. Fall: falling back down to the mat = (blank)
1. KE
2. KE converted to PE
3. PE to KE to PE
4. PE to KE
36
What does the work-energy theorem state?
The work-energy theorem states that the total mechanical work done on a rigid body is the change in mechanical energy in the
body.
37
What is the formula for the work-energy theorem?
W = ∆E = change in mechanical energy = Ef-Ei
38
What must happen for work to be applied to the body?
For a force to do work on a body there must be some displacement of the body in the direction of the force.
The work done by a constant force (F), which displaces a body through (d) metres is defined as: Newton x meter
39
What is the equation for work? in both parallel and non-parallel conditions
Wforce = Fd (when F is parallel to d)
or
Wforce = Fdcosϴ (when F is not parallel to d)
40
Work is the area done under the (blank/blank) curve
force/displacement
41
What are 2 key differences between positive and negative work?
Positive work
1. force doing work on the body (pushing a crate along the floor)
2.done by a force acting in the SAME direction as the object is displaced.
Ex. Push a box, lift weight, pull-up
Negative work
1.body doing work on the force (negative or extension phase of a biceps curl when the motion is in the downward direction but the muscle is exerting an upwards force)
2.done by a force acting in the OPPOSITE direction as the object is displaced.
Ex. Catch ball, lower weight
42
How is work calculated when force and displacement are vectors? is it a vector or scalar product?
When the force and displacement are vectors, the work done is calculated using a dot product (scalar product)
43
What is the equation of work using the dot product?
The work of a force is equal to the dot product of the force and the displacement of the body it acts upon
Wforce = F·d/ Fxdx + Fydy
44
Do isometric exercises involve doing work?
Note that the force does no mechanical work unless the object it acts upon moves (isometric muscle contractions do no work)
*Isometric contraction
–Muscle contracts
–No change in d
–No Work
45
Does the bench press involve doing mechanical work?
No!
Total Work = sum of all work completed
*Wtotal = Wlower + Wraise
*Wtotal = -700J + 700J
*Wtotal = 0
It does involve physiological work though because calories are burned
46
What is the difference between concentric and eccentric muscle actions with regards to positive or negative work?
*Concentric contraction
–Muscle shortens (elbow flexion)
–F and d in same direction
–Positive Work
*Eccentric contraction
–Muscle lengthens (elbow extension)
–Muscle F and d in opposite directions
–Negative Work
47
Can moments of a force do work? what is the unit? how is it measured?
Moments of a force can also do work
Measured in Joules (J) or KJ
Typically measured by ergometers (rowing, bike, etc.)
48
What is the formula for work done by a moment of force?
Work done by a moment of force is the product of the magnitude of the moment of force times the angular displacement of the body:
W = Mϴ (J)
49
What is the definition of power?
What is it measured in?
Power is the rate of doing work – how quickly or slowly?
Power considers not only the amount of movement a force or moment of force produces (work done), but also the time taken to do the work.
It is measured in watts
50
What is the formula for average power?
P = W/t = ∆E/t (Watts)
51
What is the formula for instantaneous power?
P = ∆E/∆ t (Watts)
52
What is the formula for power of a force when f is parallel to v?
Pforce = F·v (Watts)
Pforce = Fxvx + Fyvy (Watts)
*dot product*
53
What is the formula for power of a force when f is non-parallel to v?
Pforce = Fvcosϴ (Watts)
54
What is the formula for power of a moment of force?
Pmoment = Mω (Watts)
Defined as the product of the moment times the angular velocity of the body
55
What is the law of conservation of mechanical energy?
*The sum of energies contained in a system remain constant if no external force is applied
–Frictionless or Projectile situations
∆E = 0
Efinal – Einitial = 0
Efinal = Einitial
Epotentialf + Ekineticf = Epotentiali + Ekinetici
56
What does mechanical efficiency depend on? what is the formula for efficiency?
The efficiency of work depends on the capacity of muscle to transform substrates into muscular tension.
efficiency:
work output/work input
OR
biomechanical cost/physiological cost
57
What is the definition of kinematics?
Kinematics is the study of motion in isolation from the forces that cause the motion.
58
What are the 3 movement criteria in linear kinematics?
i. displacement
ii. velocity
iii. acceleration
59
What is the first kinematic variable?
1. Position (where to and how far?)
* the position of an object is simply its location in space
* changes in position can be described by distance or displacement
60
What is the second kinematic variable?
2. Velocity (how fast?)
* the velocity of an object is how fast it is changing its position
(Displacement/time)
61
What is the third kinematic variable?
3. Acceleration (changes in velocity?)
*the acceleration of an object is how fast the velocity is changing
(Velocity/time)
62
What are the 3 types of motion patterns in kinematics?
Translational, Rotational or Both
63
What is the definition of each?
Translational: all points in a body follow
parallel path. Can be either rectilinear or
curvilinear
Rotational: Particles within the body have
rotated with respect to their original frame of
reference
Both: Motion that happens in a single plane
and is some combination of rotation and
translation (most human movements)
64
What are the main variables of concern in linear kinematics?
Distance vs Displacement
Speed vs Velocity
Acceleration
65
What is the difference between distance and displacement?
DISTANCE:
Scalar
Measure of entire path length
Path dependent
DISPLACEMENT:
Vector
Measure of straight-line distance in a specific
direction
Path independent
66
What is the definition of velocity? is it a vector or scalar product?
Velocity: the rate of change of displacement over time.
Velocity is a vector quantity because it always has an associated direction.
67
How do you calculate average velocity?
v = ∆s /∆ t [m/s]
OR
v = sf - si /∆ t [m/s]
Where sf and si are the final and initial displacements in meters of the object and ∆t is the time elapsed in seconds.
68
What is instantaneous velocity? how do you calculate it?
Specifies how fast and in what direction one is moving at one particular point in time
Achieved by reducing the change in time drastically (ex. 1000fps)
* i.e.: time between pictures is 0.001 seconds
V=ds/dt
69
What is the difference between average velocity and instantaneous velocity?
average velocity:
the change in displacement over a finite duration
instantaneous velocity:
slope that is tangent to the displacement-time curve at a particular instance
70
What is the difference between speed and velocity?
SPEED
*Scalar quantity
*Rate of motion
*Average or instantaneous
*s = d / Δt
–Where: s = speed
d = distance
Δt = time taken
*Units are m/s
VELOCITY
*Vector quantity
*Rate of motion with a specific
direction
*Average or instantaneous
* v = Δd/ Δt = ( df - di ) / ( tf - ti )
–Where: v = velocity
Δd = displacement
Δt = time taken
*Units are m/s [direction]
71
Does average speed or average velocity typically have a higher magnitude?
How does this differ with direction?
Average speed typically has a higher magnitude than average velocity
*Straight line & rectilinear motion has speed and velocity identical
e.g.: 100m dash
*Motion changing direction – speed and velocity not the same magnitude
e.g.: 100 m swim – swimmer changes direction and average velocity = 0 because displacement = 0
72
Is average speed or average velocity usually more important in a race?
*In a race average speed is often more important than average velocity
*When start and finish = same then average velocity = 0m/s
73
what is the definition of acceleration?
What is the definition of differentiation?
When a body changes its velocity it is said to undergo acceleration
*Rate at which the velocity is changing (differentiation)
74
What is an important consideration when measuring acceleration?
How can you tell if speed changes?
Important to set-up coordinate system and record the movement because you can’t “see” acceleration
If the signs of displacement and acceleration are the same
*speed INCREASES
If the signs of displacement and acceleration are different
*speed DECREASES
75
What is the formula for acceleration? What is it measured in?
a = Vf - Vi / Tf - Ti
Measured in m/s2
76
Is each of these positive or negative acceleration?
Speeding up in positive direction (++) = (blank)
Slowing down in positive direction (-+) = (blank)
Speeding up in a negative direction (+-) = (blank)
Slowing down in a negative direction (--) = (blank)
1. positive acceleration
2. negative acceleration
3. negative acceleration
4. positive acceleration
77
When does constant linear velocity occur? How will the object move? What can we determine from it? What is the formula?
Occurs when the resultant force acting on an object is 0
Object will continue moving at constant velocity along the same straight line
If we know the object’s velocity and line of motion, we can determine the position of the object at any point in time
We can determine the final displacement of an object (sf) by knowing the object’s initial displacement (si) and the amount of time elapsed (t)
Sf = Si + vi ∆t
78
When does constant linear acceleration occur? is the acceleration known? what can we determine from it?
Occurs whenever the resultant force acting on the object is a constant. Examples: gravity, friction.
The rate of acceleration is known
If we know the initial position and initial velocity of the object, we can predict the position and velocity of the object at any instant in time.
79
What are the four constant acceleration equations?
1. Vf =
2. Sf =
3. Vf2 =
4. Sf =
1. Vf = Vi + a∆t
2. Sf = Si + vi∆t + ½a∆t2
3. Vf2 = Vi2 + 2a∆d
4. Sf = Si + ½(Vi + Vf) ∆t
80
List the angular equivalent of all these linear kinetics terms
external forces = (blank)
Mass = (blank)
Displacement = (blank)
Velocity = (blank)
Acceleration = (blank)
External moment of force
Moment of inertia
Angular displacement
Angular velocity
Angular acceleration
81
What are 2 examples where we encounter constant linear velocity?
Jogging, as in a marathon
Horizontal velocity of a projectile
82
What are 2 examples where we encounter constant linear acceleration?
friction
gravity
