boimechanics 2

torque

the turning effect produced by a force

other names for torque

moment of force or just moment

what does torque cause

changes in angular motion

where do muscle create torque

about joints

lines of action of a force

centric, eccentric, and force couple

centric force

• cause changes in translation only

• force line of action is directed through the center of gravity

eccentric force

• causes changes in translation and rotation

• force line of action is not directed through center of gravity

force couple

2 eccentric noncolinear forces, that are equal and opposite in direction

• cause changes in rotation only

moment arm

perpendicular distance between the line of action of a force and a specified axis of rotation

• shorts line between the force line of action and the axis

• represent by r

what does a moment are quantify

how eccentric a force is

what does it means if you have a longer moment arm

increases the turning effect of a force

what does a shorter moment arm do

decreases the turning effect (torque)

toque formula

T= f *r

units for toque

Nm

units for moment arm

m

what do you need to describe a torque

• specified axis of rotation

• magnitude of torque

• and sense/direction of toque

what are the directions of toque

• clockwise: negative

• counterclockwise: positive

what do we use of anatomical descriptions

the directions of torque

what happens to force as moment arm increases

force decreases

what do humans use to increase torque

tools

muscular torque

• muscle produces a pulling force

• every muscle crosses a joint

where do muscle have a moment arm

about the joint axis

where does muscle force create torque

at a joint

what does a change to a joint angle do to a muscle moment arm

changes it

what do exercise weights create

resistance torques at joints

what does muscle torque oppose

resistance troque

static equilibrium

• external forces sum to 0

• external torques sum to 0

how do you find net torque

sum up all torques

center of gravity

point in a body or system where the entire mass may be assumed to be concentrate

• changes when parts of an object change position

• not a fixed point

point of balance

what direction does the force of gravity point

downward through the cg

what does center of gravity sum up to

0

what does cg on human body depend on

on the position of each limb

when a body is projectile, what does cg follow

fixed parabolic path

what do body segments rotate around

the fixed path of cg

stability

the capacity if a body to return to equilibrium when displaced

• not easily moved or thrown

factors that affect stability

• height of center of gravity

• size of the base of support

• weight of the object

what is something that will be more stable

lower, wider, heavier

does a moment arm of a muscle change during its range of motion during activities

yes

do moment arms of a muscle change during motion or contraction?

yes

angular kinematics

the description of angular motion

angular motion

all points move in a circular path about the same axis

descriptors of angular motion

• how far

• what direction

• how fast

• speeding up, slowing down?

what is an angle

intersection of two lines, two planes, or a line and a plane

what does an angle measure

the orientation of the lines and/or planes, represented by greek theta

how many degrees in circle

360

how many degrees in a 1 rad

57.3

when do we use radians

when relating angular and linear motion

what is a revolution

complete 360 rotation

angular positon

the orientation of a line with another line or plane

absolute angular postion

one line or plan is fixed and immovable relative to the earth

orientation of a body part to the horizontal or vertical

relative angular position

both lines or planes are capable of moving

joint angle: angle between two body segments

angular displacement

Change in absolute angular position experienced by a rotating

line

Angle between the final and initial angular positions

– Angular displacement = △⍬ =⍬f −⍬i

range of motion

anatomical displacement

axis of rotation

real or imaginary line around which rotation occurs

what is the axis or rotation aligned with

a plane

what is the axis of rotation always perpendicular to

plane of motion

what happens when a segment rotates

a point farther from the axis of rotation travels a greater linear distance than a point closer to the axis

angular velocity

rate of change of angular position/ how fast the body is rotating

equation for angular velocity

w= angular displacement/ time

instantaneous angular velocity

rate of rotation at an instant in time

what type of scale is velocity

vector so has magnitude and direction

tangential linear velocity

how fast and in what direction the point is moving at an instant in time

angular acceleration

rate of change of angular velocity, when something is speeding up or slowing down

what direction is angular acceleration when speeding up or starting

in the direction of angular motion

what direction is angular acceleration when slowing down or stopping

in the direction opposite of angular motion

what does it mean when sign of velocity and accerlation are the same

body is rotating faster/ speeding up

what does it mean when sign of velocity and acceleration are opposite

body rotting slower (slowing down)

what happens to vt when w increases

it increases

tangential acceleration

component of linear acceleration tangential to the circular path

centripetal acceleration

component of linear acceleration to the center (radius/axis of rotation) of the circular path

linear acceleration

occurs when an object slows down, speeds up, or changes direction

if ⍵ is constant, ar is

directly protional to the radius

if vt constant, ar

is inversly porptional to the radius

anatomical planes

sagittal, frontal, and transverse

sagittal plane

runs anterior to posterior and superior to inferior, divides body into left and right f

frontal plane (coronal plane)

runs side to side and superior to inferior, divides the body into anterior and posterior

transverse (horizontal) plane

runs side to side and inferior to posterior , divides body into superior and inferior

anatomical axes

anteroposterior, transverse, logintudinla

anteroposterior axis

cartwheeling, Imaginary line running from anterior to posterior (sagittal axis)

• Perpendicular to a frontal plane t

traverse axis

somersaulting

– Imaginary line running from left to right (frontal axis)

• Perpendicular to a sagittal plane

longitudinal axis

twisting

– Imaginary line running superior to inferior (vertical axis)

• Perpendicular to a transverse axis

how does a segment move

within a plane and around and axis