1. Velocity and speed

2. 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

3. 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?

4. 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

5. Average vs. Instantaneous speed
Average speed is the distance traveled divided by the time to travel.
Instantaneous speed is the average speed for infinitely small distances and times.

6. 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.

7. Speed Graph

8. 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.

9. Velocity Vave = ∆x = xf - xi
Average velocity is displacement divided by the time interval
Vave = ∆x = xf - xi
∆t = tf - ti
Remember:
Displacement and Velocity can be positive or negative
Time can NEVER be negative
change in
position
units of
(m/s, km/hr)
change
in time

10. 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?

11. Example
If a car travels 25.0 km east in 15 minutes, what is the average velocity of the car?

12. Velocity can be interpreted graphically.

13. Velocity can be postive, negative, or zero (at rest)

14. Instantaneous velocity may not be the same as average velocity
Instantaneous velocity is the velocity of some instant ( or specific point on its path)