Pulleys/Levers/COG

acronym to remember levers

FLE 123

two or more forces acting on a rigid body about a fulcrum (axis)

lever

axis of rotation in a lever

fulcrum

how we can move heavy loads with small forces

OR

how we can move distal segments quickly

mechanical advantage

mechanical advantage:

how we can move ______________ loads with _____________ forces

OR

how we can move ______________ segments _______________

heavy, small, distal, quickly

3 parts of a lever system

fulcrum, effort, load

what is the external moment created by?

resistive force/gravity

what is the internal moment created by?

effort/muscle force

how to calculate mechanical advantage

internal moment arm/external moment arm (effort arm/load arm)

what are first class levers designed for?

strength (with fulcrum close to resistance/load), speed (with fulcrum close to force/effort)

counterclockwise motion = _________________ torque

positive

clockwise motion = __________________ torque

negative

in relation to body:

load = ________________

effort = ________________

gravity, muscle(s)

what are second class levers designed for?

strength

example of first class lever in body

neck extension

example of second class lever in body

calf raises

what are third class levers designed for?

speed/ROM

example of third class lever in body

bicep curl

in a bicep curl, biceps create a __________________ torque and the weight of the dumbbell creates a ________________ torque

positive (pulling counterclockwise), negative (pulling clockwise)

mechanical advantage: can do ________________ work with ________________ force

more, less

mechanical advantage gained when applying a ________________ using a __________________

force, lever

when the mechanical advantage is greater than 1, is there a mechanical advantage?

yes

when the mechanical advantage is less than 1, is there a mechanical advantage?

no

_________ 1 = mechanical advantage

_________ 1 = no mechanical advantage

greater than, less than

is there a mechanical advantage in a first class lever?

depends on where effort is (MA can be less than, equal to, or greater than 1)

is there a mechanical advantage in a second class lever?

yes

is there a mechanical advantage in a third class lever?

no

how many wheels in a stationary pulley?

one

pulley just to change the line of pull. Forces supporting the rope is equal to the vector addition of the ropes

stationary (pulley)

Pulley moves along the rope

Wheel supports the load

Effort is in the same direction as movement

Reduces the forces needed to move an object

moveable pulley

how many wheels in a moveable pulley?

two

are stationary or moveable pulleys used to lift heavy loads? why?

moveable (pulleys), force split by number of wheels

downside of moveable pulleys

takes a long time to move (the) force

how to find the force you would use to move a load with a pulley with multiple wheels

weight/number of ropes

what acts as a pulley for the quads?

patella

how does the patella act as a pulley for the quads?

increases moment arm (=more mechanical advantage)

if you didn't have a patella, how would you need to compensate?

greater quad strength

true/false: center of mass changes depending on where body is

true

base of support is bigger with ____________ contact points on ground

more

true/false: for our purposes, center of mass = center of gravity

true

point at which entire mass is considered to be concentrated

center of mass

how do canes increase base of support?

add another contact point to ground

ability to return to equilibrium

stability

stability comes at cost of __________________

mobility

3 factors that affect stability

height of COG, size of base of support, weight of object

COG height in females

55% standing height

COG height in males

57% standing height

why is COG height lower in females?

wider pelvis

why is COG height higher in males?

broader shoulders

do you have to exert more force to get up from lying down or sitting? why?

lying down (bigger moment arm)

______________ base of support = more stability

wide(r)

balance point of body

center of gravity

force of gravity on an object = _______________

weight

you are more stable if you are these three things:

lower, wider, heavier

COG over base of support = _________________ equilibrium

static

true/false: gravity produces no torque about COG

true

__________________ of a rigid body is the balance point

COG

true/false: COG always lies within the object

false

if their limbs are ________________ to their body, an ice skater can spin faster

close(r)

in anatomical position, COG is located just anterior to:

sacral vertebra 2

further COG from axis of rotation = _____________ torque generated by gravity around that axis

more

for an object made up of segments, COG is influenced by the _____________ of the segments at the position of their individual _______________

mass, COG's

in a high jump, if the jumper's COM is ________________ the pole, they need to exert less effort to jump higher. why?

below, don't have to clear COM over bar

imaginary vertical line that passes through the center of gravity

line of gravity

if line of gravity passes through _______________________, the object is stable

base of support

projection of COM into base of support

line of gravity

________________ center of gravity = better balance and stability

lower

is laying down or standing up more stable?

laying down

if you are shorter, you have a ________________ line of gravity, which indicates better ________________ and _________________

shorter, balance, stability

an angle that cancels out the torques of the weight and the applied force

tipping angle

is tipping angle higher with feet together or feet apart?

feet apart

________________ tipping angle = more stable

bigger

true/false: line of gravity affects prosthetic training

true

in a wheelchair:

purpose of rear axle angle =

purpose of front wheel size =

base of support, rolling stability

point at which all pressure is considered to be concentrated in an object

center of pressure

what is center of pressure similar to in concept?

center of gravity

pressure = _____________ /______________

force/area

examples of plantar pressures

pronation/supination, diabetic foot

examples of joint contact pressures

osteoarthritis

the scientific study of the measurements and proportions of the human body

anthropometry

for analysis, the body is considered made up of rigid __________________ connected by ________________

segments, joints

anthropometric measures that can be normalized to body weight and height (6)

length, mass, COG, moment of inertia, density, volume

body segment parameters have been obtained through what? problem with this?

cadavers, data is only for males

if you have a weak left gluteus medius, your _____________ hip will drop

right

2 components of postural control

orientation (posture), stability (balance)

area in which person can move/sway within the limits of stability or BOS

cone of stability

_______________ base of support = wider cone and more sway

wider

in kyphosis, line of gravity moves ________________

forward(s)