KIN 216 - Linear Kinematics

what is biomechanics?

the effect of forces on living systems

OR

the study of forces and their effects on living systems

what did borelli do?

contributed to scientific investigation by testing hypothesis against observation.

• studied the mechanics of animal locomotion

what did etienne-jules marey do?

interested in capturing animal movements; animal mechanism

• developed cameras that could record several phases of movement (flying pelican 1882)

  • allowed movement to be studied

who coined the term “biomechanics”?

Nikolai Bernstein

• the first ergonomist: study of the workplace

  • wanted to make the workplace safer

• examined movement during manual labour to optimise productivity (1922)

what did nikolai bernsteins research show?

that most movements are composed of smaller movements

• these little movements effect eachother

what types of equipment did they have in the 20th century to measure and record forces and motions?

cameras and pressure-sensitive equipment

what was one of the first texts, released in 1955, to emphasise mechanics/technique?

the Scientific Principals of Coaching

biomechanics is…

the study of structure and function of biological systems

define sport and exercise biomechanics:

the study of forces and their effects on humans in exercise and sport

• focus: goal-directed tasks

what is quantitative reasoning?

using numbers to try and solve a problem

what is biomechanics about

reason, model, solve problems

why biomechanics is helpful?

• PERFORMANCE IMPROVEMENT: to improve performance by improving technique, changing the equipment used, and making modifications in training

• REDUCTION AND REHABILITATION OF INJURY: to prevent or recover from injury by finding techniques to reduce injury, and designing equipment to reduce injury

what is kinematics?

describing motion over space and time

static

in a constant state of motion

• can be motionless or constant speed

• a = 0

dynamic

a change in velocity

• acceleration is present

basic units of measurement

MSK

• meters: length

• seconds: time

• kgs: mass

linear kinematics is the movement between

points

biotribology examines;

how living systems interact with objects during motion

orthodics help to:

even out the contact forces between the foot and the ground to reduce pain and discomfort

shoes with firm midsoles…

reduce the degree of lateral movement

What does it mean to move?

a change in position

how do we quantify movement?

• where we are in space (our position)

• how long the movement took (time)

linear motion

• translation

• change in position

• body moves unified, in the same direction, at the same distance

what are the two different types of linear motion?

1. rectilinear motion

2. curvilinear motion

rectilinear motion

movement along a straight line: jumping from low to high bar (pretend no swing), elevator, 50m dash

curvilinear motion

movement along a curved line: motion of a snake

linear kinematics is concerned with the description of:

linear motion

• describing where you are in space (where u began, where you finish)

• how fast it takes you to get from point a to point b

• were u in a static (constant velocity) or dynamic state

position is defined as

location in space

• could be described in 3 different dimensions

  • up/down

  • left/right

  • forward/back

to identify position, we need to identify:

a starting point for movement

what is the most common spatial system of refrence?

the Cartesian coordinate system

• measured in x and y (horizontal and vertical)

the upper right box is which quadrant?

quadrant I

the upper left box is which quadrant?

quadrant II

scalars are concerned with?

size only.

(magnitude)

ex. distance, speed, pace

vectors are concerned with what?

magnitude and direction

ex. displacement, velocity and acceleration

the length of the arrow indicates what of the vector

the size/magnitude

the total length of travel =

distance

the change in position =

displacement

speed and velocity both measure how fast or slow a system moved BUT speed measures __________ and velocity measures ___________

speed measures change in distance (this is a scalar quantity)

velocity measures change in displacement (vector quant

pace is:

how many minutes it takes someone to run a km

it is the inverse of speed

gives runners something to brag about, everyone can run 5k but everyone does it at a different time

change in time / change in distance

for aceleration to be present, what must also be present?

• a force must be present; forces are what produce a change in velocity

dynamic motion is characterised by a change in…

velocity

acceleration is

the change in velocity / change in time

if the final velocity is greater than the initial velocity, then a is

positive

if the final velocity is smaller than the initial velocity, then a is 

negative

if the final velocity is equal to the initial velocity, then a is _________ and the system is in a ________ state

0

static

velocity is constant

pediatricians use linear kinematics for 

assessments

coaches use linear kinematics for 

teaching movements

therapists use linear kinematics for 

therapy

movement is described over

a period of time

(t2 - t1)

characteristics of average time period

occuring over a designated interval of time?

• typically a longer time period

• simplified, overall behaviour

characteristics of instantaneous time period?

occuring during a finite interval of time

• typically during a smaller time period

• describing motion at critical time intervals

differentiation

obtaining information using another value

• the process of going from displacement to velocity to acceleration

• how much a quantity is changing at a given point. allows you to calculate the slope of the proceeding quantity

• CALCULATING THE SLOPE

the slope =

rise / run

y2 - y1 / x2 - x1

the slope of a displacement vs. time graph at any given point is equal to… ?

the velocity at that given point

the slope of a velocity vs. time graph at any given point is equal to… ?

the acceleration at that given point

integration

obtaining information using another value

• the process of going from acceleration to velocity to displacement

• to bring together / incorporate parts into a whole

• CALCULATING THE AREA UNDER THE SLOPE

the area under the slope of a velocity vs. time graph is equal to… ?

the displacement

the area under the acceleration vs time graph is equal to… ?

the change in velocity

would a bullet fired horizontally from a gun, or another bullet dropped from the same height, hit the ground first?

• they would hit the ground at the same time because horizontal and vertical components are independent of each other therefor analyzed separately

what is a projectile?

a body projected into the air or dropped from a height

• the moment it is in the air, there are no other forces acting upon it other than gravity or air resistance

projectiles are ONLY under the influence of… ?

air resistance and gravity

• if air resistance is too small to measure, the only force acting upon it is gravity

what is the acceleration due to gravity?

-9.81 m/s2

or

9.81 m/s2 downward

if the force of gravity is constant, this means that… ?

the acceleration of the system will not change (uniform acceleration)

vertical and horizontal components are analysed seperately because?

1. the two components are independant of each other 

• gravity only influences vertical motion (up/down)

• air resistance only influences horizontal motion

2. once a body is projected into the air, velocity is constantly

trajectory

the path travelled when describing projectile motion

initial velocity on projectile motion:

IS NOT equal to 0, in a projectile motion there will always be that initial velocity because it was being launched into air

apex

the highest point in the travelled path of a projectile motion

in a projectile motion, acceleration is… ?

constant

range

the maximum horizontal displacement travelled

if the take off and landing heights are the same, what does that mean for the total (horizontal) time in terms of the vertical time up?

the verticle time up is equal to the verticle time down, therefore the verticle time up is half the total (horizontal) time.

if you have the time it takes to get to horizontal you can times that by 2 to get total time

what three factors effect projectile motion

• projection speed (vi)

• projection angle (theta)

• relative projection height

what is terminal velocity

as an object is free falling the force of gravity is always acting upon it, meaning that projectiles continue to accelerate while in free fall

as the speed of the system increases, an upward air resistance is created,

the drag force, acts opposing to gravity as a type of friction,

eventually, the drag force will equal the gravitational pull on the system

AT THE POINT the object ceases to accelerate and continues to fall but at a constant speed.

this is called terminal velocity

what effects terminal velocity?

the projected area

what are the laws of constant acceleration

• the force of gravity os constant so the acceleration of the system will not change (uniform acceleration)

• horizontal and vertical components of a projectile are independent of each other

v2 = v1 + at

v2² = v1² + 2ad

d = v1t + (1/2)at²

in a projectile, what determined the motion?

the initial conditions