midterm 2 Flashcards
angular position (normal, absolute, and relative)
angular position: orientation of a line with another line or plane
absolute: angle of a single body segment with respect to a known vertical or horizontal
relative: angle of one segment relative to another.
specifically the angle between longitudinal axes of two segments
absolute segment angles
calculated using the trigonometric relationship: tangent= opposite over adjacent
to calculate absolute leg angle: proximal segment coordinate values are subtracted from the distal end coordinate values
the ratio of y to x defines the tangent of the angle
relative angles how to calculate?
law of cosine: side of the traingle that dont contain a right angle
axis rotation
rigid body
axis rotation: fixed line about which a rigid body rotates
always perpendicular to its plane
sagital ml
frontal ap
transverse lognitudinal
rigid body: a body that maintains a constant shape when rotated (bones)
right hand rule
clockwise is negative
counterclockwise is positive
angular distance vs displacement
angular distance: sum of all angular changes (scalar)
angular displacement: difference between the final and initial positons (vector)
linear vs angular displacement
when an object or rigid body rotates, it undergoes both linear and angular displacement
linear displacement of a point on a rotating object or rigid body is directly proportional to the distance that point is from the axis of rotation
greater the radius: greater the linear displacement
linear is related to angular but not proportional to it
angular speed vs velocity
angular speed: is the angular distance travelled per unit of time (scalar)
angular velocity: charaterized by the Greek letter omega (w), is a vector quantity that desribes the time rate of chnage of angular position (rad/s or degrees/s or rpm)
angular velocity= angular displacement divdied by time
angular acceleration
angular acceleration= a greek letter alpha
rate of change in angular velocity measured in radians per second squared (rad/s 2) or in degrees per second squared
a= w/t
angular kinematics
angular motion occurs when all parts of the body move through the same angle but do not undergo the same linear displacement
the subset of kinematics that deals with angular motion is angular kinematics, which describes angular motion without regard to the causes of the motion
unit of measurement (degreee, revolution/ # of rotations, radian)
degree: one circle/one complete= 360 degrees
revolution/# of rotations: one circle= one revolution
radian: one circle= 2 pie radians
1 rad= 57.3 degrees
force
vector quantity: magnitude and direction
what does it do? a force involves the interaction of two objects and can produce a change in the state of motion of an object by pushing or pulling it
force= mass x acceleration
unit: newton (N)
1N= Amount of force it takes to accelerate a 1kg body at 1m/s 2
often represented as a ratio of force to body weight (BW)= %BW
newtons three laws of motion
1) law of inertia: a body will remain at rest or continue to move with a constant velocity unless acted upon by an outside force
inertia: used to describe an objects resistance to motion and is directly related to the mass of a object
newtons second law
law of acceleration:
f=ma explains the effect of the net force
net force= mass x acceleration
unit of force is newtons (N)
* a force applied to a body causes acceleration of that body:
of a magnitude proportional to the force
in the direction of the net force ex) tug o war
and inverslet proportional to the bodys mass
Newtons 3rd law: action/reaction
for every action there is an equal and opposite reaction
force always acts in pairs
these paired forces are equal and opposite
jumping off the ground
indvidual exerts force on ground
ground exerts force on the individual
inertia what is it?
how to overcome it?
used to describe an objects resistance to motion and is directly related to the mass of an object
inertia your acceleration will be 0 due to having a constant velocity
overcome inertia, to get something to move, the force needs to be greater than the inertia/mass of object
if this occurs, the object will be accelerated in the direction of the applied force
momentum
momentum (P): the quantitiy of motion of an object
product of the objects mass and linear velocity
the faster an object moves with more mass, the greater the momentum
p=m x v
accleration
a force applied to the body causes an acceleration of the body
of a magnitude proportional to the force
amount force applied= amount acceleration felt on object
in the direction of the net force
and inversely proportional to the bodys mass
rearranging newtons second law (acceleration)
F= ma
f= m x v/t
f= m x v / t
p= m x v
force is equal to to the time rate of change of momentum
conversion of momentum
in the absence of external forces momentum is constant
only external forces will change the motion of a system
example
two people colliding but not bouncing off each other
means both momentums would equal 0 because momentum before would be the same as momentum after
impulse
linear impulse is the product of a force and the time interval over which a force acts
change in linear momentum
I= Ft
I= P2-p1 or m2v2 - m1v1
tangential vs centripetal
tangential: acceleration tangent to the rotation segement
centripetal: acceleration along the segement towards the axis
body weight and mass are different
body mass is scalar
body weight is a vector
main types of force
gravity
ground reaction force
friction
fluid resistance
joint reaction forces
inertial force
muscle force
elastic force
ground reaction force
the weight of a person standing in the anatomical neutral position generates a reactor force by the ground that is equal in magnitude and opposite in direction to the weight
external force acting on the body
propulsive force
breaking force
propulsive force: a fore that is causing a body to speed up
breaking force: a force that is causing a body to slow down
GRF in walking vs running
walking: max vertical GRF = 1-1- 1.2 BW
one peak for 1st half of support, valley during knee flexion at full support, then second peak as push off the ground
running: maximum vertical GRF component= 2-5 BW
shape depends on footfall pattern of runner
friction
a force that acts parallel to the interface of two surfaces that are in contact during motion (impending motion)
direction is opposite of motion
ex: block sliding on a flat surface slide
pulling force needs to be greater than the friction force
friction= coefficient of friction x normal force
kinetic friction
static friction
friction that allows movement= kinetic friction
kinetic friction is less than the static friction and changes according to the speed of object
friction that is large enough to disallow movement= static friction
normal force
is the force perpendicular to the surface
inertial force
one body segment can exert force on another segment , causing movement at that second segment without muscle exertion
typically a more proximal segment exerts an inertial force on a more distal segment
coefficient of friction
unitless number
indicates the relative ease of sliding.
greater coefficient= harder to slide (carpet)
less coefficient= easy to slide (water, ice)
friction in athletic contects
skaters like fresh ice low coefficient because easier to slide
golfers wear gloves to increaase coefficient of friction and get a better grip on the club
fluid resistance
air resistance
water resisitance
both greatly affected by two components:
ex: density of air greatly affected by humidity, temperature, pressure
viscosity: (a measure of the fluids resistance to flow)
water is more viscous than air
drag force: always act to oppose the motion
lift force: always afcts perpendicular to the drag force
produced by a break in the symmetry of airflow
seams on a ball
joint reaction forces
segments are often analyzed separtely
ex) while standing still, at the knee joint you can examine:
the upward force of the lower leg on the thigh
the downward force of the thigh on the lower leg
net force across the knee joint: joint reaction forces
muscle force
muscle can generate only a pulling force
ex: the biceps brachii can pull on its insertion on the forearm to felx the elbow
ex: the triceps brachii can pull on itds insertion ont he forearm to extend the elbow
static equilbrium
no acceleration
system is at rest or at constant velocity
example tug a war
elastic force
force applief to a material can result in a change in length in that material
F= k s
k=stiffness
s= change in length
ex: diving board
work: effect of force applied over a distance
work: the product of the magnitude of the force applied to an object and the distance the object moves in the direction of applied force
unit joule (j) or newton-meter (Nm)
w= f x d or w= f x cos x s
directional work
the object is moved in the same direction of force
negative work: the object is moved in the opposite direction of the force
cocentric= + work
eccentric= - work
power
the amount of wokr done per unit of time (the rate of mechanical work)
units is watts (w) or 1 j/s
P= w/t
greater power is quicker
power can also be seen as force x velocity if you rearrange
simultaneous kinetic chain linking
sequential kinetic chain linking
simultaneous; activation of multiple muscle groups and segments at the same time
ex) power clean
sequential: activation of muscle groups and segments at different times throuhgout the movement
ex) baseball throw
energy
capacity to do work
various types of energy: light, heat, nuclear, elctrical and mechanical
two main types of mechanical energy:
kinetic: refers to the energy resulting from motion
potential: refers to the capactiy to do work because of position or form.
an object may contain stored energy, for example, simply becasue of its heigh or its deformation
kinetic energy
KE= 1/2 mv squared
Ke is the ability of a moving object to do work resulting from its motion
0 velocity= no KE
change in velocity= great increase in KE
potetntial energy
energy due to an objects position (capacity to do work)
PE= Wh (weight x height)
PE= mgh (mass x gravity x height)
total energy= KE + PE
COM location
human body is not a rigid object so the location depends on position of extremtities
importance of COM
stability: resistance to linear and or/ angular acceleration \
balance: ability to control equilibrium. in order to balance, the athletes COM must be located within the support base.
principles of stability
how to improve stability
increase body mass
increase friction between the body and contact surface
increase size of support base in the direction of the line of action of the external force
horizontally position COM near the edge of support base on the side of oncoming external force (no external force than COM in middle of support base)
vertically positioning COM as low as possible (linebacker)
pressure
force per unit area
1 N per m squared equal to 1 pascal
units pascal (Pa) and kilopascal (KPa)
P= f/a
