BBiomechanics midterm II Flashcards
what is mechanical work?
product of force and displacement in the direction of that force
means by which energy is transferred from one object to another
why is average force uses for U (mechanical work)
because usually the force applied is not constant
what are the three types of muscle contraction how does this reflect in work?
isometiric (static) = 0 work
concentric. = shortening = postiive work
Eccentric = lengthenign = negative work
What is mechanical energy
the capacity to do work
what is kinetic vs potential energy?
objects capacity to do work due to motion of the object
vs due to position of object
is energy always positive?
yes
do changes in mass or velocity have large effects on KE
velocity (it is squared)
Is Kinetic energy conserved?
No as during impact some KE is converted to other forms like sound and heat
what are the 2 types of potential energy
- gravitataion PE
- Strain energy
What is gravitational PE?
PE due to objects position relatie to earth
What is the case for g in pe?
IT is always positive
what is strain energy?
PE due to the deformation of an objet like bending pole in pole vault, stretched muscle or tendon
what s k in strain energy? what is delta x?
stiffness constant. deformation or change in length
What is the work-energy relationship?
the work done by external forces (other than gravity) acting on an object causes a change in the energy of the object
U= delta E which is Delta KE + Delta PE (we wont incldue strain energy)
How do we maximize kinetic energy (in sports spec)?
large force applied over long distance
What an example of a technique used when doing work to decrease energy?
Flexing lower limb joins to minimize impact - increaing displacement.
How do we do work to decrease energy?
we use techniques and materials to perform negative work on an object to absorb some kinetic energy by increasing displacement of an object to minimize impact force
What is the conservation of mechanical energy?
in the absence of external forces (other than gravity) no work is done and total mechanical energy is constant or conserved
KEi + PEI = (KEf + PEf)
Ei = Ef
In projectiles what happens to KE and PE:
1) before an object is dropped?
2) as it falls?
3) The instant before object strikes ground?
before dropped KE = 0
as it falls PE decreases because height deceasee but KE increases cause it acc due to gravity
Instant before the object strikes the ground it has no PE because h=0
How are PE and KE related in projectiles while falling?
The decrease in PE is equal to the increase in KE
what is power?
The rate of doing work
definition of linear power
product of average force and average velocity
P = U
Δt P = Fd
Δt P = F d
Δt P = Fv
as the velocity of a contraction increases, the maximal force the muscle can generate …
decreases
What decrease w age?
isometric muscle strength
power is affected by an age related change in either ____ or ___
strength or velocity
What is peak effort reffered to as?
Maximal voluntary contraction
How is angualr velocity measured?
isotonically - fixed load moved thru a range of motion as fast as possible
How is maximal muscle power achieved? Usuallt at ___ of maximal velocity.
not at fastest velocity or largest force but rather a compromise between the 2. 1/3
as duration of an activity increases, the power output which can be sustained _____
decreases exponentialy
What are the 4 elements of a lever? How many classes are there?
lever, fulcrum, force, load. 3
What is the axis of rotation called on a lever?
fulcrum
where is the fulcrum in a class one lever - where is force and load
classs 2?
class 3?
- fulcrum in the middle
Force down on one side and load down on the other ( ex= seesaw/skull-atlas joint) - Fulcrum on one side
Load down in middle
force up on edge (ex = stanidn on toes gastroc or wheelbarrow) - fulcrum on one side
load down on end
force up in the middle
(ex = elbow joint or tongs or tweezers)
what is torque defined as?
the turning effect produced by a force
what are 3 types of ecternal forces, explain them?
- centric force = external force thru centre of gravity - no angualr motion only linear (f=ma)
- Eccentric force = not directed thru the centre of gravity
liner and angular motion - Force couple - none colienrar forces equal in size but opp indirection - angular only - no change in linear motion
What is the moment (forec or leaver) arm (r) ?
perpendicular distance between the line of action of force an a parallel line passing thru axis of rotaion
What is torque equal to?
the product of the size of force and the moment arm
T = what for centric forces?
0
How do we increase torque in humans?
large moment arms
to fully categorize a torque what must one describe?
size of torque, axis which turn effect is created, direction of turning
is clockwise positive or negative?
negative
what rule determines direction of torque?
right hand thumb rule
what is responsible for movement of our limbs about our joints?
torque
where is line of action (pull) for a muscle force generally?
along the line between tendons
Does the moment arm of a muscle change?
yes with joint angle - maximal is at 90 degrees
What is the vertical component called muscular torque?
rotary component
when msucle force pulls at an angle what produces torque?
only the compenent of force perpendicular to the bone (lever) - rotary component
What acts to stablize or dilocate the joint?
Horizontal force or the force parallel to the bone
what is the rotary component, stabilizing component and dislocating component ?
rotary = vertical, dislocating = contract/right (on graph)
Stablizing = horixontal pointing left on grapj
if net force = 0 can there be linear motion? angular motion?
no to linear but yes to angular
For an object to be in static eqm what must sum to 0?
external forces and external torque
What is centre of gravity defined as?
point in body around which its mass or weight is balanced and through which the force of gravity acts
what happens to the torques at the CG?
torques cerated bye each element sum to 0
where is CG of the human body ? left to right and front to bacK? tope to bottome?
l to r: midline of body
Back to front- thru shoulder and hips jsut forward of ankle joined
Top to bottom - 55% of standing height for females and 57% of standing height for males
Why do children fall over/
they have a higher centre of gravity because of their alrge heads and short legs
what happens to CG when u abduct ur right arm?
CG moves right
What is stability?
the capacity of anobejct to return to equillibrium or orignal position after being displaced
what is an objects stability affected by?
height of CG (lower is better)
size of base of support (larger is better)
Weight (heavier is better)
What does it mean by stability being directional
an object can be more or less table depending on the direciton of the toppling force
How are stability and PE relatied?
CG height is raised as object is toppled
increase in cg heaht leads to an increase in PE
Whys is the object with lower CG more stable?
The lwoer the original CG heigh, the greater the increase in height of CG as object is toppled, therefore the increase in PE is geater and more work must be done
What is the most stable psotion for a person or object to be in?
One that minimizes PE - CG below rather than above the points of support
If CG is BELOW base of support what happens to object?
It will return to its original position after displacement (stable equilibrium)
How is stable equillibrium achieved
- object returns to its original position if CG is below base of support
what is angular kinematics
the description of angular motion
what is angular position? absolute vs relative?
orientation of a line relative to another line or plane
Absolute has a fixed reference line/plane
Relative has a moveable one
What are radians related to?
movement around a circle
With linear motion around a circle, radians ____ when you multiply by the radius
dissapear so its just m/s not r x m/s
How many degrees in one radian?
57.3 degrees
how do u get degrees to radians
multiply by pi over 180
radians to degrees connversion?
x 180/pi
what is angular diplacement? what is the symbol?
the change in absolute angular position of a rotating line
angle formed between the final and initial position of a rotating line
Unlike linear motion with angular displacement we consider _____ and ____ the same
distance travelled and diaplcement
Linear distance (not displacement) travelled by a point on aline is porportional to what?
distance from axis of rotation (radius) and angular displacement in RADIANS
What is l? formula?
arc length/linear distance
l = delta angle (angular disp)times readius
linear DISPLACEMENT is porpotional to what?
distance from axis of rot (radius) but NOT angular displacement
what is chord length?
Linear displacement (d), a chord is a line joining any 2 points on a curve
What is a mechanical disadvantage for torque production
Muscles attach close to joints which is small moment arm and there for small torque
What is a mechanical advantage for linear displacement?
small movement near join produces large linear displacement at distal end of limb - hockey - putter
what is w lookin thing?
angular velocity
what is angular velocity? what letter does it look like?
rate of change of angular displacement - w - veecnto - rad/s or degrees/sec or rpm
how long it takes someth
What is AVERAGE angular velocity important for?
What is INSTANTANEOUS?
how long it takes msth to rotate form A to B - sumersaults, twists
Instantaneous - important if we want to know how fast smth is rotating at given time - relevatn to sport wher a bat/stick/club strikes and object like baseball
which are the same for all points on a line out of angular velocity and angular displacement?
BOTH
Linear distance (arc length ) increases w //
radius/distance from axis of rotation
What is instantaneous linear velocity equation? what does VT, w and r mean?
VT is instantanous tangential lienar velocity
w is isntantanus angualr velocity
r is radius length
what is a tangent?
a line which touches a circle at only on point and is perpendicular to the radius
What is a mechanical advantage for linear velocity?
small movement at joint produced 8 times linear displacement at wrist - linear velocity also 8 times greater
what is angular accelration?
rate of change of angular velocity? - vector rad/s^2 or deg..
what three things cause angualr acceleration?
spin fster, spin slower, axis of spin changes
What are the two types of instantaneous linear
acceleration associated with angular motion?
Tangential acceleration (at a tangent to circular path)
f
2. Centripetal acceleration (toward the axis of rotation)
What is a and r in tanegenital acceleration (aT)
α is the instantaneous angular acceleration (rad/s2)where:
r is the radius length
To maintain an object ona. circular path what is needed?
centripetal/radial acceleration
what would happen to an object without centipital accelaration
onject would travel in striaght line at a tangent circle
what is Vt r and w in ar (centirpeatl acc) formula
Vt is isntantaneous linear velocity r is radius w is agnular velocity
