Exam 2 Review Questions Flashcards
When a pendulum starts from rest and swings 20 degrees in 2 seconds, the average angular velocity is:
10 Degrees
True or False? When swinging your extended arm around in a circle (in a sagittal plane), your elbow has a greater arclength than your wrist?
False
If a pendulum swings forward 30 degrees and then back 10 degrees, the angular distance and displacement are:
distance: 40 degrees, displacement: 20 degrees
True or false? If a body is rotating with a constant angular velocity, the angular acceleration AND the linear, centripetal acceleration of the body are zero.
False,
Even with no angular acceleration, constant angular motion gives rise to a nonzero centripetal acceleration.
The lowercase, Greek letter omega is the symbol used for angular acceleration.
False
Alpha
True or False? If a body segment is rotating with a constant angular velocity, the angular acceleration of the segment AND the linear, tangential acceleration of a point on the distal end of the segment are zero.
True
True or False? One degree is larger than one radian?
False
a radian is larger than a degree
The linear velocity of a point on a body undergoing angular motion is equal to?
(radius)*(angular velocity) where radius is the distance from the axis of rotation to the point.
An angle calculated between the thigh and a horizontal plane is?
An absolute angle
Angular velocity is measured in what units?
Radians/seconds
What is the angle of the knee joint in the anatomical position?
180degrees
With a constant, non-zero angular velocity, the tangential linear velocity of a rotating point about the axis is:
For a given angular velocity of a golf swing, the linear velocity of the head (distal end) of a long club compared to a short club will be:
The motion of the arm during a properly executed throwing motion is such that:
the proximal segments begin to rotate prior to the distal segments.
Consider a person standing in the anatomical position. The moment of inertia of the body rotating about the longitudinal axis is __________ the moment of inertia about the anteroposterior axis.
What is the biomechanical purpose of the patella?
It increases the moment arm of the knee extensors, thus creating more torque for a given muscle force.
Angular momentum can be expressed mathematically as:
moment of inertia * angular velocity
True or False? Angular momentum of a body is not influenced by the application of linear forces to the body
False
As moment of inertia decreases what happens to angular velocity and angular momentum?
he moment of inertia of a moving body is specific to the:
Axis of Rotation
During a dive, if a diver goes from a full layout position to a tuck position, what will happen to her angular velocity?
Increase
Torque is the angular analog of what?
Force
Units for angular momentum and torque?
Angular Momentum: kg m^2/sec
Torque: Newton (N)
Joint torque is influenced by:
- Muscle Force
- Moment Arm
True or False? The torque experienced by a system is the angular effect of the linear forces applied to it
True
Moment of inertia is the angular analog of what?
If angular momentum is NOT conserved, what measure will allow us to predict changes in angular momentum?
When the knee is flexed from anatomical position, what happens to the moment of inertia about the vertical axis of the hip?
increased
When knee is flexed from anatomical position, what happens to the moment of inertia of the leg about the medio-lateral axis at the hip?
decreased
In a movement where angular momentum is conserved there must be:
No net external torque
A tailwind acting to push a sprinter during a 100 m race would increase the relative velocity of the runner in regard to the air, decreasing the race time for the sprinter.
What is Center of Pressure
The point of application of a dynamic fluid force acting upon a body
True or False?
A tailwind acting to push a sprinter during a 100 m race would increase the relative velocity of the runner in regard to the air, decreasing the race time for the sprinter.
False
True or False?
Consider two objects with the same size, shape, and velocity but different masses flying through the same air at the same time, although the same drag force is applied to both objects the EFFECT of the force on the momentum of each is different.
True
SI unit for Density
Kg/m^3 (kilogram per cubic meter)
What orientation do drag and lift act in relation to one another?
Always perpendicular (90 degrees)
Where does the buoyancy force act upon a body?
Laminar flow
A flow characterized by smooth, parallel layers
Factors that influence drag
-fluid density
-projected area
-coefficient of drag
-Relative velocity
What is viscosity?
The resistance to float
What are the components of dynamic fluid force?
Drag and Lift
What is the SI unit of specific weight?
N/m^3 ( Newtons per cubic meters)
True or False?
The bouyant force exerted on an object is due to the relative motion of that object in the fluid
False
Fluid Related Forces
Drag
Lift
Buoyancy
Overall Fluid Resistance
True or False?
One cubic meter of air is heavier than one cubic meter of water
False
True or False?
The buoyancy of a swimmer is influenced by the total body volume of a swimmer
False: only the submerged volume.
What is Magnus Force
lift force created by spin
What is the Magnus Effect?
deviation in trajectory of a spinning object toward the direction of spin
The dimples of a golf ball allow it to fly further in the air by decreasing the:
Form Drag
For a ball moving through the air, which of the following pairs of velocities represent the highest relative velocity?
ball v = -20 m/s; air v = 20 m/s
The point of application of a bouyancy force acting on an object is at the ________________ of the object.
Center of Volume
The point of application of a dynamic fluid force acting upon a body is at the ____________ of the body.
Center of Pressure
What type of angle is shown?
relative angle
What type of angle is shown?
Absolute angle
r
radius
α
angular acceleration
ω
angular velocity
a (subscript r)
radial acceleration
Σ
the sum of
Which of the following factors influence muscle force production?
Myofilament type
Physiological cross sectional area
Muscle gender
Muscle location
PCSA
Torque depends on which of the following?
Magnitude of Force
Point of force application
moment arm of the force
all of the above
All of the above
Which of the following depicts moment arm?
C
When the forearm is in a state of static equilibrium (i.e., no movement):
All torques must sum to zero
All torques must sum to a positive number
All torques must sum to a negative number
I have no clue what you are asking
All torques must sum to zero
The center of gravity of the body is:
a fixed, never-to-move, point in the body
a point around which body weight is equally distributed
a point which is NOT influenced by the motion of arms and legs
A point about which body weight is evenly distributed
Consider the elbow flexor, biceps brachii. What elbow joint angle results in the largest moment arm for this muscle?
30 degrees
60 degrees
90 degrees
135 degrees
90 degrees
If there are three eccentric forces and two centric forces acting about the elbow how many torques are acting about the elbow?
3
What is a radian?
the ratio between the circumference of a unit circle and the length of its radius (1)
Relative Angle
Joint angle, angle of two segments
Absolute angle
Angle between a segment and a reference plain (i.e. shank wrt horizontal plane)
Joint angle is represented by which greek letter?
theta
Hypersupination
arch strike excessive load on fibula
Hyperpronation
Collapsing arch (instep strike) excessive load on tibia
Unit for angular displacement
radians
degrees to radians
(deg) * pi / 180
tangential velocity units
radians/s
how does radius effect velocity?
longer radius greater velocity
Correct anatomical throwing sequence
proximo distal
pelvis trunk upper arm forearm hand
Angular Acceleration Units
rad/s squared
Tangential Aceleration definition
linear acceleration of a point of interest
Centripital Acceleration Synonym
Radial acceleration
Radial Acceleration definition
rate of chagne in direction of a body in angular motion
For a given r, higher Vt is related to higher what?
radial acceleration
What do rotational and curvilinear motions result in?
radial acceleration
Centrifugal Forces
force that acts outward on a body moving around a center, arising from the body’s inertia.
Centripital Force
a force that acts on a body moving in a circular path and is directed toward the center around which the body is moving.
Consider a yoyo being spun in the air which component demonstrates centripital force?
the string pulling the yoyo in
Considera yoyo being spun in the air which component demonstrates centrifugal force
the yoyo at the end, if released would fly outward
Linear and Angular analogs
d
v
a
theta
little omega
little alpha
If the angular acceleration of the forearm is zero, then:
1 angular velocity is zero
2 angular velocity is constant
3 both 1 & 2 could be correct
4 neither 1 nor 2 are correct
3
True or false: Joint angles are relative angles
True
Rearfoot angle is calculated from two segment angles, which are measured in the ______ plane.
Frontal Plane
RF angle
Rearfoot Angle
Units of tangential acceleration
m/s squred
When running around a curve on the track, in which lane is it more difficult to maintain your direction, with the same linear velocity (i.e., you have a higher centripetal acceleration)?
1 Outside
2 Inside
3 Centripetal acceleration is same for all lanes
Inside
What are the units of centripetal acceleration?
m/s squared
If there are three eccentric forces and two centric forces acting about the elbow how many torques are acting about the elbow?
3
Moment of intertia depends on which elements?
Mass and Distribution of mass
What are the units of radial acceleration?
m/s squared
What does resistance to angular motion depend on?
Distribution of mass
Mass
Radius of gyration symbol
k
What is radius of gyration
represents the object’s mass distribution with respect to a give axis of rotation.
Newtons 1st law of angular momentum
a rotating body will maintain a state of constant angular motion unless acted on by an external torque
Newtons second law
T= I alpha
a net external torque exerted on a body is directly proportional to the rate of change in angular momentum (angular motion)
Newtons third law of angular motion
for every torque exerted on one body there is an equal and opposite torque exerted by a second body on the first
The moment arm associated with a torque is:
a distance which is perpendicular to the force
If you hold a cat upside down and drop it, the cat’s TOTAL angular momentum during flight will be:
Zero the entire flight
If the angular acceleration of the forearm is zero, then:
angular velocity is zero
angular velocity is constant
Fluid Definition
A substance that flows when subjected to a sliding force
Four Properties of a Fluid
Pressure
Density
Specific Weight
Viscosity
Pressure
Force / area n/m squared
Density
littel rho
mass / volume kg/m cubed
specific weight
little gamma
weight / volume n/m cubed
Viscosity
resistance to flow (internal friction)
Two types of flow
laminar
turbulent
laminar flow
fluid molecules lowing parallel to one another, smooth, ordered
turbulent flow
fluid molecules mix in a random manner, chaotic, onordered
Fluid forces
Immersion : buoyancy
Dynamic: Drag and Lift
Drag and Lift make up?
total fluid resistance
buoyancy
upward force
fluid reaction force
archimedes principle
buoyant force is equal to the weight of the fluid displaced by the body (Fb= Vd(gamma)
Formula for determining if an object will float?
Fb= BW
Density of air
1.2 kg/m cubed
buoyancy of air
1N (.2lbs)
when will a body experience a buoyant force?
When it is immersed in fluid
When will a dynamic fluid force occur?
when relative motion occurs between the body and the fluid
Drag
opposes motion
lift
acts perpendicular to flow
relative velocity
vfluid - vbody
types of drag
surface drag
form drag
surface drag
force acting on the surface of a body (skin friction)
How is surface drag reduced?
reducing roughness or surface area
form drag
force created by pressure difference between front and back sides of a body
how is form drag reduced?
streamlining, dimples on golf ball
terminal velocity
acceleration equals zero
lift
force acting perpendicular to fluid flow
magnus effect
deviation in trajectory of a spinning object toward the direction of spin lift force created by spin
Overall Air Resistance
Resultant vector of lift and drag
OAR squared = lift squared + drag squared
What is the buoyancy force a reaction to?
weight of the fluid displaced
