KNS 372 Exam 2 Material

angular motion

all parts of a body move through the same angle

angular displacement

change in angular position or orientation of a line segment

difference in the initial and final angular positions of a moving body

vector

degrees, rads, revolutions

radian

the size of the angle subtended at the center of a circle by an arc equal in length to the radius of the circle

“pure number”

how many radians is 360 degrees

2pi radians

angular distance

sum of all angular changes that have occurred

actual angular angles covered from initial to final position

scalar

counterclockwise direction

positive

flexion

clockwise direction

negative

extension

angular velocity

angular displacement divided by change in time

angular acceleration

rate of change in angular velocity

(velocity/time)

two perpendicular linear acceleration components

tangential acceleration

radial acceleration

tangential acceleration

PATH

represents the change in linear speed

is TANGENT to the curved path

linear acceleration that describes the ROC in magnitude of the tangential velocity vector

radial (centripetal) acceleration

CENTER

represents change in direction of an object following a curved path

directed toward the center of curvature (middle of the circle)

angle measurement

an angle is composed of two sides (lines) that intersect at a vertex

uses a goniometer

segment (absolute) angles

measured from an external frame of reference

(measured counterclockwise from the right horizontal in bm)

instant center of rotation

precisely located center of rotation at a joint at a given instant in time

joint (relative) angle

angle formed between two limb segments

measured as a segment moves away from the anatomical position

quadrants

zero

straight fully extended position at a joint is ____ degrees

thigh-trunk

hip angle=

thigh-leg

knee angle=

foot-leg-90

ankle angle=

inertia

resistance to a change in an object’s state of motion

directly proportional to an object’s mass

mass (m)

quantity of matter in an object

kg

force

a push or pull

f=ma

newtons, kg*m/s²

characteristics of force

1. magnitude (in newtons)

2. direction (+-)

3. point of application

free body diagram

sketch that shows a defined system in isolation with all of the force vectors acting on the system

net force

single resultant force derived from the composition of all the acting forces

determines the overall effect of all acting forces on a system or free body

center of gravity

point around which the body’s weight is equally balanced

aka balance point, axis of rotation

weight (wt)

amount of gravitational force acting on the body

equal to mass x gravity

Newtons

pressure (P)

force distributed over a given area

P=F/A

Pascals=N/m²

torque (T)

the rotary effect created by an eccentric force

T=Fd (perpendicular distance)

Newton-meter Nm

Impulse (J)

the product of force and the time over which it is applied

J=Ft

Newton-second (Ns)

compression

pressing or squeezing force directed axially through a body

tension

pulling or stretching force directed axially through a body

shear

force directed parallel to a surface

mechanical stress

• inside the body structure

commonly used to describe force distribution within a body when an external force acts on it

N/m²

bending

asymmetric loading

produces tension on one side and compression on the other

torsion

occurs when a structure is caused to twist about its longitudinal axis, typically when one end of the structure is fixed

combined loading

presence of more than one form of loading

MOST COMMON

deformation

change in shape

effects of loading

1. deformation

2. acceleration

yield point

“elastic limit”

point past which deformation is permanent

ultimate failure point

produces mechanical failure

repetitive loads

repeated application of a subacute load that is usually of relatively low magnitude

can also result from repeated sustenance of forces

“chronic, stress injury”

“microtrauma”

acute loads

application of a single force of sufficient magnitude to cause injury to a biological tissue

“acute macro trauma”

law of inertia (1)

a body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state

law of acceleration (2)

a force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass

law of action and reaction (3)

when one body exerts a force on a second body, the second body exerts a reaction force that is equal in the magnitude and opposite in the direction to the first

ground reaction force (GRF)

every contact of a foot with the floor or ground generates an upward reaction force

(related to performance and injury)

law of gravitation

any two particles of matter attract one another with a force directly proportional to the product of their masses and inversely proportional to the square of the distance separating them 

frictional forces

opposes sliding or motion between objects in contact

maximum static friction (Fm)

maximum amount of friction that can be generated between two static surfaces

dynamic (kinetic) friction (Fk)

friction force present during motion

friction

a force acting at the interface of two surfaces in contact during the motion or impending motion of one surface

coefficient of friction

index of the interaction between 2 surfaces in contact

unitless # indicating the relative ease of sliding

normal (perpendicular) reaction force (R/N)

the force exerted by a surface on an object that is in contact with it, acting perpendicular to the surface

momentum

quantity of motion

M=mv

kg*m/s or N*s

Vector

conservation of momentum

in the absence of external forces, the total momentum of a given system remains constant in a closed system

M1=M2

perfectly elastic collision

“bouncy” collision

• no energy lost

• initial velocities and final velocities are the same 

• sum of momentums are the same

perfectly inelastic collisions

“sticky” collisions

• no rebound or bounce

• travel at the same speed afterwards (stuck together)

coefficient of restitution

ratio of pre- (u) and post-collision (v) velocity

0

coefficient of restitution for a perfectly inelastic collision

1

coefficient of restitution for a perfectly elastic collision

breaking impulse

decelerating (dec. horizontal momentum)

negative impulse, positive momentum (opposite directions)

propulsive impulse

accelerating (inc. horizontal momentum)

positive impulse, positive momentum (same directions)

impulse-momentum relationship

rate of change in momentum produced by the force changes the impulse

Impulse=change in momentum

reduce momentum

impulse and momentum in opposite directions, impulse will…

increase momentum

impulse and momentum in the same direction, impulse will…

work

force causes a change in position

W=Fd

scalar

average force

direction of the force

distance of object

three things needed to know work

power

amount of work performed in a given time

scalar

P=W/t=F*V

best mechanical indicator of the intensity of physical task—analogous to VO2

Watts

energy

the capacity to do work

three forms determined by motion, position, or state

kinetic energy

energy of motion

a moving object has the capacity to do work due to its motion

potential energy

energy associated with an object’s vertical position with respect to some reference height, usually the ground

changes due to position

conservation of mechanical energy

when the gravity is the only acting external force a system’s mechanical energy is conserved

ME=PE+KE

strain (elastic) energy

whenever an object has the ability to return to its original shape after being deformed