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
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