Transcript Velocity and Acceleration

Velocity and speed
Objectives
 Compare and Contrast speed and velocity
 Use correct SI units to express speed and velocity
 Describe and analyze motion in one dimension
using equations for speed, instantaneous velocity,
and average velocity.
 Generate and interpret graphs and charts
describing motion using speed and velocity
Motion
 An object is in motion when there is a change in
position when compared to another object

It’s a rate of change in position over a period of time
Pause video for a moment and think about this
question…..Do all objects move at the same rate?
How do we represent this?
Speed
 A scalar quantity of the rate of change in position.
 Magnitude with units but no direction
 Units for distance are m, cm, km (etc)
 Units for time are s, min, hr
 Most common units for speed are m/s and km/hr
Average vs. Instantaneous speed
 Average speed is the distance traveled divided by
the time to travel.
Total Distance Covered
Average Speed 
Travel Time
 Instantaneous speed is the average speed for
infinitely small distances and times.
DistanceCovered
Instanteneous Speed 
In Minim alTim e Am ount(~ 0)
5. Graphing speed: Configuration
 Slow walker: Walk slow and steady.
 Fast walker: Walk briskly but steady.
 Fast starter: (Starts fast and than slows down):
Run in a full sprint at the beginning. Be fast around
15m and then slow it down during the last 15m
(second half of the trip).
 Fast finisher: (Starts slow and than speeds up):
Begin with a walk, jog somewhere around 15 m
and run in a full sprint by 25m.
Speed Graph
Graphing Speed: Data Set 1
35
Constant
slow motion
30
Distance [m]
25
Constant
Fast Motion
20
15
Slowing
Down
10
5
Speeding up
0
0
5
10
15
Time [s]
20
25
Velocity is not the same as speed
 Speed – has no direction (scalar)
 Velocity – has both speed and direction (vector)
Pause for a moment and think about the differences between the
two and how their graphs may look different.
Velocity
 Average velocity is displacement divided by the
time interval
change in
position
Vave = ∆x = xf - xi
∆t = tf - ti
units of
(m/s, km/hr)
change
in time
Remember:
Displacement
and Velocity
can be
positive or
negative
Time can
NEVER be
negative
Example
 During a race on level ground, Andra runs with an
average velocity of 6.02 m/s to the east. What
distance does Andra cover in 137 s?
Example
 If a car travels 25.0 km east in 15 minutes, what is
the average velocity of the car?
 Velocity can be interpreted graphically.
 Velocity can be postive, negative, or zero (at rest)
 Instantaneous velocity may not be the same as
average velocity
 Instantaneous velocity is the velocity of some instant
( or specific point on its path)