CH. 5 Linear motion of the system

what happens to momentum in collisions?

conservation of momentum -momentum before collision=momentum after collision

rate of motion is NOT always

constant

without external forces, the spatial and temporal characteristics of motion (kinematics) remain

constant

without forces (kinetics), kinematics remain

constant

uniform motion

constant motion

acceleration = 0 at

constant motion OR at rest -equilibrium

projectile motion follows a ___ path

curvilinear

ground reaction force is

decelerating

decelerating means

decrease in momentum

increasing the time over which you allow the earth to change your momentum...

decrease the force on your body

if something is speeding up and going right, direction= ___ acceleration= ___

direction + acceleration +

if something is slowing down and going right: direction= ___ acceleration= ___

direction + acceleration -

if something is going at a constant speed (no change) and going right: direction=___ acceleration = __

direction + acceleration 0

if something is slowing down and going left: direction=___ acceleration=___

direction - acceleration +

if something is speeding up and going left, direction=___ acceleration=___

direction - acceleration -

if something is going at a constant speed (no change) and going left: direction=___ acceleration=___

direction - acceleration 0

drag force

dynamic fluid force acting in opposite direction of motion

work is an

energy transfer

newton's law of gravitation

every body attracts every body =force is product of masses/ square of separation

translation/linear motion (3 qualifications)

every point moves at the -same time -same direction -same distance

if an object is already in motion and traveling a given velocity, there is no change in that velocity unless

external force applied

law of acceleration

f=ma -acceleration directly proportional to force magnitude -acceleration inversely proportional to mass

law of action/reaction forces

for every action there is an equal and opposite reaction -forces exist in pairs

motion does not require a

force

kinematic values are measurements of the system exhibited by the system as a result of

force application Kinetics

kinetic measurement tool: *primary measurement tool in biomechanics

force plate

linear impulse is the product of

force x interval of time of force application

kinetics are

forces

___ is required to generate horizontal (anteroposterior and mediolateral) forces

friction

greater force =

greater change in linear motion

acceleration is directly proportional to force means

greater force= greater acceleration

acceleration is inversely proportional to mass means

greater mass= less acceleration (heavy, can't move quickly)

more force required to stop motion=

greater momentum

force plate measures

ground reaction force

the time over which you apply a force makes a difference...this is called

impulse

accelerating means

increase in momentum

in order to increase the impulse and momentum,

increase time to which you can apply a force

any movement made while airborne is caused by ___ forces

internal

linear impulse (J)

interval during which force is applied

SI unit of work

joules

example of this:

jump down from something you don't lock your knees. bend knees and slow down, increase time in which you allow earth to change your momentum and decrease the force put on your body.

units for momentum

kg m/s

units for momentum:

kg x m/s

the forces involved are the study of

kinetics

newton's second law:

law of acceleration

newton's third law:

law of action/reaction forces

newton's first law:

law of inertia

what is the vector version of linear distance traveled?

linear displacement

center of pressure (COP)

location of the resultant GRF Ax, Ay

because of varying ____, equal and opposite forces can produce unequal reactions

mass

momentum can be gained by increasing (2 things)

mass or velocity

peak rate of motion:

max velocity acheived

weight (w)

measures gravitational force upon mass -mg

free moment (T2) -what type of motion

moment about vertical axis through Center of pressure -twisting motion

average net force x time interval of force application=

momentum (m(Vf-Vi)

greater momentum=

more difficult to stop motion

projectile motion

once in motion, nothing can change path except external forces

when an object is slowing down, the acceleration is in the ___ direction of velocity

opposite

example of linear impulse:

pitcher wind up

center of pressure is the average

point on force plate where pressure is equally distributed around

Newton's first law (law of inertia) can also be written as

principle of conservation of linear momentum

peak velocity is not that important, in many activities it is more important how

quickly you can change your velocity (accelerate)

average acceleration:

rate of change in velocity/entire interval

instantaneous acceleration:

rate of change of velocity at one instant in time

instantaneous velocity

rate of motion at one given instant in time

newton's first law helps us understand:

relationship between kinematics and kinetics

equation for speed (s)

s= l/DT -speed= linear distance traveled/change in time

when an object is speeding up, the acceleration is in the ___ direction of velocity

same

linear distance traveled is a

scalar

internal forces change the

shape of the system

Ax

shifts forward or back

Ay

shifts side to side

kinematics are

spatial and temporal descriptions of movement

inelastic collision

stick together -share a common final velocity

plumbob:

string with weight

if linear velocity does not change then

system does not accelerate -acceleration=0

momentum (M)

system's quantity of motion

if you stand on one foot, center of pressure is within

that one foot (below it)

for mechanical energy,

the object has to move in order for work to be done

speed (s)

the scalar rate of motion

kinetics

the study of forces that inhibit, cause, facilitate, or modify motion

displacement will NEVER be greater than

total distance traveled

linear distance traveled (l)

total length of the path traveled by the system

unless a force acts upon the system,

total momentum remains constant

linear motion is also called

translation

if acceleration is greater than 0, positive

v final > v initial (positive change in velocity)

velocity (v) equation:

v=d/Dt -velocity=displacement/change in time

linear displacement is a

vector

momentum is a ____

vector

What is the vector rate of motion?

velocity

friction is not required to generate ___ force

vertical (z)

which component of GRF has largest magnitude>

vertical (z) -gravity, body weight

Change in velocity calculated by

vf-vi

how does force plate work:

when you step on it, it causes structural changes in metal, the electrical current generated is analogous to force

shod running

with shoes -heel strike (shin splints)

abebe bikila

won olympic marathon in rome on cobblestone barefoot

if you attach a plum bob to center of gravity and let it come to rest,

would track where COG is above the force plate

width of plate

x (front to back)--anteroposterior

length of plate:

y (side to side)--mediolateral

vertical

z (body weight)

work can be

+ or -

for projectile motion, acceleration in y direction is

-9.8m/s2

units of impulse:

N s

does the person in the race who has the highest peak/instantaneous velocity necessarily win the race?

NO

so we have to calculate:

-average rate of motion: -average speed -average velocity

two other things to look at in force plate besides GRF:

-center of pressure -free moment

collision equations depend on: (5)

-degree of stick -elasticity -friction -air resistance -gravity

Linear kinematics (4)

-displacement -velocity -direction -acceleration

2 types of collisions

-elastic -inelastic

law of inertia

-every body at rest remains at rest or in uniform motion in a straight line unless a force acts upon it

barefoot running: difference

-land on forefoot -no heel strike (no initial peak of Vertical GRF)

linear kinetics (4)

-momentum -work -power -energy

force transducers have 2 things

-piezoelectric sensors -strain gauge

translation 2 types:

-rectilinear -curvilinear

force plate directions: (3 components of GRF)

-vertical (Z) -anteroposterior (X) front to back -mediolateral (Y) side to side

force plate data has 6 quantities of interest:

-z GRF -x GRF -y GRF -center of pressure Ax -center of pressure Ay -free moment (twist)

at equilibrium, the sum of all forces =

0

at rest, acceleration=

0

at rest, velocity=

0

constant motion (no change in velocity), acceleration =

0

without linear displacement, velocity is equal to

0 -no change in position

for projectile motion, acceleration in x direction is

0 -because velocity is constant

force plate has a ____ coordinate system

3D

center of pressure is mapping where the

Center of gravity is on the force plate (monitors balance)

average speed/velocity:

calculated over a significant time interval

change in motion...

DOES require a force

linear displacement (d or Dp)

change in linear position of the system in a straight line

law of gravitation formula:

F=Gm1xm2/r2 -r2=separation

instantaneous acceleration equation:

F=ma

work=

Fd force x distance

average acceleration equation:

Fnet=mDv/Dt

linear impulse equation

J=FnetDt

linear impulse (J) is not the same as

Joules (SI unit for work)

equation for momentum (M)

M=mv -mass x velocity

linear acceleration (a)

change in rate of motion (vector rate of motion) -change in velocity

if acceleration is less than 0, negative

V final < V initial (negative change in velocity)

kinematics:

a measurement of the motion exhibited by the system as a result of force application

equation for acceleration (a)

a=Dv/Dt -acceleration= change in velocity/change in time

the observed change in motion is called

acceleration

equilibrium

at rest or constant velocity

at equilibrium:

at rest, acceleration=0 constant motion, acceleration=0

what tells who won the race

average velocity

center of pressure assesses

balance

if you stand on both feet center of pressure is

between the two

elastic collisions

bounce off

since linear displacement is a vector, it can be

broken down in x and y components