Week 2: Torque and Levers

torque is an ____ force

angular

what are the four components of force?

1. magnitude

2. point of application

3. line of application (line of action)

4. direction

when the lever arm is longer, you get ___ ___ with the same amount of force

more torque

muscle can only shorten or lengthen along the ___

striations

what are the four important parts of torque?

1. axis of rotation

2. magnitude of force applied

3. distance from axis to applied force

4. angle (direction) of force

moment arm (lever arm)

straight line distance to point of application of perpendicular force component

angle of insertion

formed by bone axis and tendon insertion, changes muscle and joint forces

____ causes torque

force

shorter moment arm requires ___ force for same amount of torque

less

the greater the force, the greater the ____ force

tangential

tangential force

does all the rotation

parallel force

does compression and distraction

how does a long moment arm influence torque?

makes it greater

equilibrium

all torques applied are equal

if there is no equilibrium (not static), where does the direction of rotation occur?

in direction of greater torque

effort force

force causing the rotation of the lever

resistance force

force opposing the rotation of the lever

effort arm

moment arm of effort force

resistance arm

moment arm of resistance force

first class lever

2 parallel forces applied on either side of an axis creating rotation of the lever in opposite directions

what is an example of a first class lever in the human body?

flexion and extension of the neck

second class levers

resistance force applied closer to the axis than the effort force

in second class levers, ____ is always greater than ____

effort arm; resistance arm

third class lever

2 parallel forces applied at some distance from the axis; effort force is closer to axis than the resistance force

in third class levers, the _____ force is always greater than _____ ____

resistance; effort arm

what is a common third class lever in the body?

flexing bicep

what is the most common lever in the body?

third class

the closer the load is to your axis, the shorter the ___ ___, reducing torque on your elbow

resistance arm

mechanical advantage

describes efficacy of a lever system

the more efficient the lever system, the ___ force needed to overcome a large resistance

less

if you have a long effort arm, you have more/less efficient mechanical advantage

more

which lever is more efficient, type II or type III?

type II

what is an example of an anatomical pulley in your body?

A1 pulley in the hand, patella, olecranon

what is the function of anatomical pulleys?

increase mechanical advantage so a muscle can produce greater force

stress

force on an object that might cause it to deform

what are some different examples of stress?

tensile stress, compressive stress

strain

change in shape of an object due to stress

what are the three principle stresses?

1. tension

2. compression

3. shearing

what are three types of loads?

1. axial loads

2. bending loads

3. torsional loads

why is shearing important to consider in OT?

maintaining skin integrity

axial loads

stress or force applied along axis of an object

bending loads

stress or force applied in same plane on a different line

torsional loads

stress or force applied around long axis of an object

elasticity

material is able to immediately return to its original size and shape when stress is removed

plasticity

material retains some of its stressed size and shape when stress is removed

viscoelasticity

material does not deform instantaneously when loaded, but does change over time

what is an example of elasticity in the body?

skin

what is an example of plasticity in the body?

stretching your hamstrings every day will cause them to lengthen over time

what is an example of viscoelasticity in the body?

ligaments

Wolff’s Law

bones in the body will adapt to loads under which they are placed over time

Davis’s Law

tissues in the body will be shaped by mechanical stresses placed upon them