Linear Kinematics

Describing Objects in Motion

Define Motion:

»Motion is...

Define Motion:

»Motion is a change in position over a period of time.

Space and Time

Types of Motion

Linear Motion (translation)» all points on the body move

– the same distance– in the same direction– at the same time

» Rectilinear Translation: straight line– figure skater gliding across the ice

» Curvilinear Motion: curved line– free-fall in sky-diving

Types of Motion

Linear Motion (translation) Angular Motion (rotation)

» all points on the body move – through the same angle

» Whole body rotation– giant swing, pirouette

» Segment rotation– flexion, abduction, yada yada yada ….

Types of Motion

Linear Motion (translation) Angular Motion (rotation) General Motion

» combines angular and linear motion» most common type of human movement

– pedaling a bike– walking– drawing a straight line

Linear KinematicsDescription of Linear Motion

»how far? »What direction? »How fast? »Speeding up, slowing down?

Position Identifying location in space

» at the start of movement?» At the end of movement?» At a specific time in the midst of movement?

Use a fixed reference point» 1 dimension

– starting line, finish line

» 2 dimension– Bloomington-Normal: north, east, south, west– (goal line, sideline), (0,0), Cartesian coordinate system

Recall: Vector & Scalar Quantities

Scalar: Fully defined by magnitude» mass

Vector: Definition requires magnitude and direction» force

Distance and Displacement

Measuring change in position» component of motion

Football player: » receives kickoff at 5 yard line, 15 yards from

the left sideline» runs it back, deking defenders over a twisted

48 yard path, to 35 yard line, 5 yards from the left sideline

Distance and Displacement

Distance» length of path traveled: 48 yards

Displacement»straight line distance in a specified

direction»y direction: yfinal - yinitial

»x direction: xfinal - xinitial

Distance and Displacement

Resultant Displacement»length of path traveled in a straight line

from initial position to final position–y direction: yfinal - yinitial

–x direction: xfinal - xinitial

Components ofresultant displacement

R2 = (x)2 + (y)2

Distance and Displacement

Resultant Displacement»length of path traveled in a straight line

from initial position to final position–y direction: yfinal - yinitial

–x direction: xfinal - xinitial

Components ofresultant displacement

R2 = (x)2 + (y)2

= arctan (opposite / adjacent)

Speed and Velocity Measuring rate of change in position

»how fast the body is moving speed

»scalar quantity–how fast

Speed =time

distance

Speed and Velocity Measuring rate of change in position

»how fast the body is moving speed

»scalar quantity–how fast

Speed =time

distance meters

seconds

Examples

Who is the faster runner:» Michael Johnson

– 100m in10.09s– 200m in 19.32s (world record)– 300m in 31.56 s– 400m in 43.39s (world record)

» Donovan Bailey (Maurice Greene)– 50m in 5.56 s (world record)

» http://www.runnersweb.com/running/fastestm.html

QuizWhat 1970’s rockband is named

after a gymteacher?

Instantaneous Speed

We have calculated average speed»distance by time to cover that distance

Maximum speed in a race? »Make the time interval very small

» 0.01 second or shorter

Speed and Velocity Measuring rate of change in position

»how fast the body is moving speed velocity

»vector quantity– how fast in a specified direction

velocity =time

displacement m

s

ExampleSwimmer

»100 m race in 50 m pool»24s and 25s splits

Calculate velocities & speeds» first length, second length» total race (lap)

Example

Football player: » receives kickoff at 5 yard line, 15 yards from the

left sideline» runs it back, deking defenders over a twisted 48

yard path, to 35 yard line, 5 yards from the left sideline

time is 6 seconds Calculate velocities & speeds

» forward, side to side, resultant

Use speed to calculate time

Running at 3 m/s How long to cover 2 m?

Projectile Motion

Click here to go to a siteshowing

the predictabilityof projectile motion

(applied kinematic equations)

Or here for a site on the high jump.

Use these concepts, make yourself $$$$

QuizIf a body is traveling in the + direction and it undergoes a – acceleration, the body will ____________________.

If a body is traveling in the – direction and it undergoes a + acceleration, the body will ___________________.

Speed up or slow down

Acceleration Quantifying change of motion

» speeding up or slowing down» rate of change of velocity

Acceleration = velocity

time

vf - vi

tf - ti

=

Soft landing from 60 cm

80% 1RM BP, Narrow vs Wide Grip