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# biomechanics final*

### chapters 10-14

statics covers situations in which all forces acting on the body are balanced (in equilibrium)
dynamics branch of biomechanics, dealing with bodies subject to unbalance
kinematics branch of mechanics that considers the forces that produce or change motion
scalar quantities single quantities (size or amount
vector quantities double quantities (magnitude and direction)
relative motion- the act or process of changing place or position with respect to some reference object
translatory motion object is translated as a whole from one location to another
rectilinear motion- the straight-line progression of an object as a whole with all its parts moving the same distance in the same direction at a uniform rate of speed
curvilinear motion- refers to all curved translatory movement (moves in curved pathway)
angular/rotary motion- when an object acting as a radius moves about a fixed point.
reciprocating motion denotes repetitive motion
external factors modifying motion- friction, air resistance, water resistance
internal/ anatomical factors modifying motion- friction in joints, tension of antagonists. ligaments and fascia, anomalies of bone and joint structure, atmospheric pressure inside joints, presence of interfering soft tissues
speed equation= distance/ time
velocity equation= displacement/time
mean acceleration= final velocity- initial velocity/ time
a= v/t
v= at
t= v/a
factors that control the range of a projectile: speed of release, angle of projection, and height of release
angular displacement equation= C=2(pi)r
force- that which pushes or pulls through direct mechanical contact or through the force of gravity to alter the motion of an object
what kind of quantity is force? vector!
force possess both... magnitude and direction!
internal forces- muscle forces that act on various structures of the body
external forces- outside the body (weight, gravity, air or water resistance, friction)
magnitude is directly affected by what? muscle fibers
point of aplication point at which force is applied to object
anatomical pulley- patella- the patella increases angle of pull and increases rotary component
law of inertia- body continues in its state of rest of uniform motion unless an unbalanced force acts upon it
law of acceleration- F=mass x acceleration, acceleration is directly proportional to force causing it and inversely proportional to mass of object
impulse- Ft= m(v-u) product of force and time is applied
momentum= mass x velocity
What are linear forces? give an example. forces applied in same direction along the same action line ex) gastrocs and soleus acting at ankle joint, psoas and iliacus acting at hip joint
What are concurrent forces? give an example. forces acting at the same point of application but at different angles. ex) several fball players blocking each other in blocking situation
What are parallel forces? give example. forces are not in the same line but parallel to each other act at different points on body ex) holding a 10 N weight in hand with arm flexed at 90 degrees
conservation of momentum- in any system where forces act on each other, the momentum is constant
What are the 6 forces that modify motion?? 1) gravity 2) reaction forces 3) weight 4) friction 5) elasticity and rebound 6) fluid forces
what is friction? the force that opposes efforts to slide or roll one body over another
friction is proportional to? the force pressing two surfaces together
what is elasticity? the ability of an object to resist distorting influences and to return to its original size and shape when the distorting forces are removed.
coefficient of elasticity- e= the square root of bounce height/ drop height
The size of the rebound angle compared with that of the striking angle depends on the elasticity of the striking object and the friction between the two surfaces
a ball coming in with backspin hitting the floor has a smaller angle of reflection
balls thrown with topspin will rebound from horizontal surfaces lower and with more horizontal velocity than that with which they struck the surface true
balls hitting a horizontal surface with backspin rebound at higher bounce and are slower
a ball with no spin will.. develop some top spin on the rebound
a ball hitting with topspin will... develop greater topspin when rebounding
laminar flow if fluid around an object is smooth and unbroken
drag force result of pressure on the leading edge of the object and the amount of backward pull produced by turbulence on trailing edge
Bernoulli's principle- the pressure in a moving fluid decreases as the speed increases
eccentric force- a force whose direction is not in line with the center of gravity of a freely moving object or the center of rotation of an object with a fixed axis of rotation
torque- the turning effect of an eccentric force, or moment of force
torque equation= torque = force x moment arm (t=f x d)
moment arm- the perpendicular distance between the force vector and the axis
force couple- effect of equal parallel forces acting in opposite directions
principles of torques- resultant torques of a force system must be equal to the sum of the torques of the individual forces of the system about the same point.
What is a lever? a simple machine that operates according to the principle of torques; a rigid bar that can rotate about a fixed point when force applied to overcome resistance
fulcrum- fixed point about which a lever turns when force applied
effort arm (EA)- the perpendicular distance between the fulcrum and line of force of the effort
resistance arm (RA)- the perpendicular distance between the fulcrum and the line of resistance force
first class levers- axis lies between the effort and the resistance
mechanical advantage of first class levers- balance
second class levers- resistance lies between axis and effort; EA always longer than RA
advantage of second class levers- magnifying the effects of effort so takes less force to move resistance
disadvantage of second class levers- ROM sacrificed
third class levers- effort leis between axis and resistance; Ra always longer of the two moment arms
principle of levers- a lever of any class will balance when the product of the effort and the effort arm equals the product of the resistance and the resistance arm.
1st class lever abbreviation EAR
2nd class lever abbreviation ARE
3rd class lever abbreviation AER
anatomical examples of first class lever- head on neck, forearm when being extended by triceps against resistance
anatomical examples of second class lever- calf muscles
non-anatomical examples of second class levers wheel barrow, door handle, nutcracker
anatomical examples of third class lever most muscles, biceps
non-anatomical third class lever- screen door with spring closing
principle of levers equation= E x EA = R x RA
mechanical advantage- ability to magnify force
MA also = EA/RA
moment of inertia equation- I = sum mr^2
angular momentum= moment of inertia x angular velocity (lw)
conservation of angular momentum- total angular momentum of a rotating body will remain constant unless acted upon by external torques
a decrease in moment of inertia produces.. an increase in angular velocity
what is center of gravity? the balance point or the point about which a body would balance without tendency to rotate
location of center of gravity of human being in normal standing position varies with: body build, age, and sex
females approximate COG (center of gravity)= at 55% of standing height
male approx COG= at 57% standing height
convert revolutions per second to radians per second multiply rev/ sec x 360 then divide by 57.3
convert radians per second to degrees per second multiply by 57.3
Created by: sbush0804