The Conditions of Rotary Motion Flashcards by Ellie Mondok

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

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The turning effect of an eccentric force

Torque

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Torque = ___________ x ________

magnitude of the force; length of the moment arm

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The perpendicular distance from the line of force to the axis of rotation

Moment arm

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As the moment arm decreases, the torque ____________

decreases

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As the magnitude of the force decreases, the torque ___________

decreases

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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

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The torque of a segment due to gravity can be changed only by changing the ______ __ ___ ________ ___.

length of the moment arm

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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

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Only the rotary/stabilizing component of the muscle force vector is actually a factor in torque production.

rotary

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The rotary/stabilizing component of the muscle force vector acts along the mechanical axis of the bone through the axis of rotation.

stabilizing

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True or false: the stabilizing component of the muscle force is not eccentric.

True

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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

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Equal parallel eccentric forces applied in the same direction on opposite sides of the center of rotation will initiate _______ motion.

Linear; no

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Equal parallel forces applied in opposite directions on opposite sides of the center of rotation will initiate _______ motion.

rotary

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The effect of equal parallel forces acting in opposite directions

force couple

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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.

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Clockwise torques are positive/negative.

negative

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Lever

A rigid bar that can rotate about a fixed point when a force is applied to overcome a resistance

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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

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When there is no motion, the torque produced by effort and the torque produced by resistance are _______, making the lever system _________.

equal; balanced

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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

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True or false: Nearly every bone is a lever

True

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Portion of lever between fulcrum and force application

Lever arm

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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