The Conditions of Rotary Motion Flashcards
A force whose direction is not in line with either the center of gravity of a freely moving object or the center of rotation of an object with a fixed axis of rotation.
Eccentric force
The turning effect of an eccentric force
Torque
Torque = ___________ x ________
magnitude of the force; length of the moment arm
The perpendicular distance from the line of force to the axis of rotation
Moment arm
As the moment arm decreases, the torque ____________
decreases
As the magnitude of the force decreases, the torque ___________
decreases
True or False: In the human body, the weight of a segment can be altered simultaneously.
False, the weight of a body segment CANNOT be altered simultaneously
The torque of a segment due to gravity can be changed only by changing the ______ __ ___ ________ ___.
length of the moment arm
Muscle forces that exert torque are dependent on which two things?
Point of insertion of the muscle
Changes in length, tension, and angle of pull
Only the rotary/stabilizing component of the muscle force vector is actually a factor in torque production.
rotary
The rotary/stabilizing component of the muscle force vector acts along the mechanical axis of the bone through the axis of rotation.
stabilizing
True or false: the stabilizing component of the muscle force is not eccentric.
True
Once a muscle force is resolved into a rotary and stabilizing component, the moment arm is the distance between the ____________ and the ________________
axis of rotation
point of application of the rotary component of the muscle force
Equal parallel eccentric forces applied in the same direction on opposite sides of the center of rotation will initiate _______ motion.
Linear; no
Equal parallel forces applied in opposite directions on opposite sides of the center of rotation will initiate _______ motion.
rotary
The effect of equal parallel forces acting in opposite directions
force couple
The Principle of the Summation of Torques
The resultant torque of a force system must be equal to the sum of the torques of the individual forces of the system about the same point.
Clockwise torques are positive/negative.
negative
Lever
A rigid bar that can rotate about a fixed point when a force is applied to overcome a resistance
What are the two functions of a lever?
1.) Overcome a resistance larger than the magnitude of the effort applied
2.) Increase the speed and range of motion through which a resistance can be moved
When there is no motion, the torque produced by effort and the torque produced by resistance are _______, making the lever system _________.
equal; balanced
What are the three main purposes of external levers?
1.) Small force overcomes large resistance
2.) Large range of motion overcomes small resistance
3.) Balance force and load
True or false: Nearly every bone is a lever
True
Portion of lever between fulcrum and force application
Lever arm
The effort arm is the perpendicular distance between the fulcrum and the ________ __ _______ __ ______.
line of force of effort
The resistance arm is the perpendicular distance between the fulcrum and the _______ __ __________ _____
line of resistance force
In a ______-______ lever, the axis lies between the effort and the resistance.
first-class
In a first-class lever, if EA = RA, then the lever is used to ____________.
Balance two or more forces
In a first-class lever, if EA > RA, then the lever favors ______________
force production
In a first-class lever, if RA > EA, then the lever favors _____________
speed and range of motion
Example of an anatomical first-class lever
Head tipping forward and backward
In a ________-_______ lever, the main function is force production at the cost of range of motion.
second-class
In a second-class lever, the EA is greater/less than the RA.
Greater
Example of an anatomical second-class lever..
Forearm in slow downward extension
In a _______-______ lever, the main function is speed and range of motion at the cost of needing a greater effort to overcome resistance
third-class
In a third-class lever, the EA is greater/less than the RA
Less
Example of an anatomical third-class lever
Forearm flexed by biceps and brachialis; arm abducted by deltoid muscle
Four functions of a simple machine:
1.) Balance two or more forces
2.) Favor force production
3.) Favor speed and range of motion
4.) Change the direction of the applied force
A lever of any class will balance when __________.
E x EA = R x RA
When a lever has an EA longer than its RA, it favors ____________.
force
When a lever has an RA longer than its EA, it favors _____________.
Speed and range of motion
True or false: In angular movements, speed and range are interdependent.
True
The EAs in the skeletal lever systems of the human body are determined by the _____________________ and the ___________________.
point of muscle attachment
muscle angle of pull
Anatomical levers tend to favor ______________ at the expense of _______.
speed and range of motion
effort
Short levers enhance ____________ ________ while sacrificing _____ ______ and ________ __ _______
angular velocity
linear speed, range of motion
Strength needed to maintain angular velocity increases/decreases as the lever lengthens
increases
The ability to magnify force
Mechanical Advantage
The mechanical advantage of a lever is the ratio of _______________ overcome to ________ applied.
resistance; effort
9 questions that should be answered for every lever:
1.) Where are the fulcrum, effort application, and resistance application?
2.) At what angle is the effort applied to the lever?
3.) At what angle is the resistance applied to the lever?
4.) What is the EA of the lever?
5.) What is the RA of the lever?
6.) What are the relative lengths of the EAs and RAs?
7.) What kind of movement does this lever favor?
8.) What is the mechanical advantage?
9.) What class of lever is this?
A body continues in a state of rest or uniform rotation about its axis unless acted upon by an __________ _____.
external force
The acceleration of a rotating body is directly/indirectly proportional to the torque causing it, is in the same/different direction as the torque, and is inversely proportional to the moment of inertia of the body
directly
same
When a torque is applied by one body to another, the second body will exert an ______ and __________ torque on the first.
equal, opposite
As the distance between the axis and the mass increase, inertia increases/decreases
increases
The moment of inertia depends on _________ and ________.
quantity of the rotating mass
mass’s distribution around the axis of rotation
What is the moment of inertia?
The size of angular inertia
Moment of inertia equation
I = Σmr²
If the mass of an object is concentrated close to the axis of rotation, the object is easier/harder to turn because the radius for each particle is more/less
easier
less
True or false: Body position has no effect on mass distribution, and therefore no effect on inertia
False
Which has greater inertia? A tuck or a pike?
A pike
What is the angular equivalent of linear force?
Torque
What is the angular equivalent of mass?
Moment of inertia
What is the angular equivalent of linear acceleration?
Angular acceleration
Torque equation
T = Iα
Angular momentum equation
Angular momentum = Iω
Law of Conservation of Angular Momentum
The total angular momentum of a rotating body will remain constant unless acted upon by external torques.
When an ice skater spins, bringing her arms closer to the axis of rotation, the moment of inertia increases/decreases about that axis.
decreases
True or false: A force that causes a change in angular momentum must have an equal and opposite force creating an equal and opposite momentum change
True (Newton’s Third Law)
The angular velocity of two moving parts is inversely proportional to their _________ __ ______ about the axis of motion.
Moments of inertia
True or False: For every angular action in a plane, the reactions must be in the same or parallel planes.
True
Centripetal Force
A constant center-seeking force that acts to move an object tangent (at right angles) to the direction in which it is moving at any instant, thus causing it to move in a circular path
Centrifugal Force
Outward-pulling force working on a body moving around a center, arising from the body’s inertia
Centrifugal force is equal in magnitude to _____________.
centripetal force
Equation for centripetal force:
F꜀ = mv²/r
When a runner turns a tight corner, as centripetal force increases, the amount of lean will have to increase/decrease.
increase
