1. Speed and Velocity
11.2

2. Speed A B C Speed: The ratio of the distance an object moves
To the amount of time the object moves
SI Unit of meters per second (m/s)
Average Speed:
Total distance divided by total time
Example
While traveling on vacation, you measure the times and distances traveled. You travel 35 kilometers in 0.4 hours, followed by 53 kilometers in 0.6 hour. What is your average speed?
Instantaneous Speed:
In this trip, did you go 88 km/hr the ENTIRE time?
Your car’s speedometer measures instantaneous speed
88 km/h
35 km in 0.4 hrs
53 km in 0.6 hrs A B C

3. Graphing Motion A distance-time graph is a good way to describe motion
Imagine you measure the distance a car went every other second
Here’s what you record for car A:
For car B:
Can you see this:
What would the STEEPNESS (slope) of these lines mean:
The slope of a line on a distance-time-graph is
SPEED
Car A covers 100 meters every second
100 m/s
Car B covers 100 meters every 2 seconds
100 m / 2s = 50 m/s

4. Graphing Varying Speed
What does it seem this car is doing:
He’s going fast from t = 0 s to t = 3 s
He’s stopped from t = 3 s to t = 7 s
He’s going slow from t = 7 s to t = 10 s
How fast is he going?
Fast = 200 m/s
How slow is he going?
Slow = 50 m/s

5. Velocity Caracas is about 200 km away from here
You could get there in 2 hrs
Speed?
100 km/h
If you go 100 km/h, will you get to Caracas?
You need a direction
What was the difference between
Distance
Displacement
One of them has a direction
Same here:
Speed
Velocity
Velocity = speed + direction

6. Combining Velocities
Sometimes the motion of an object involves more than one velocity
Like a boat in a fast moving river:
If the river carries a current of 5 km/h East
A boat with its motor set for 12 km/h East
How fast does the boat look like it is going from the ground?
Vector addition, X + Y = Z
17 km/h
5 km/h
12 km/h

7. Combining Velocities
Sometimes the motion of an object involves more than one velocity
Like a boat in a fast moving river:
If the river carries a current of 5 km/h East
A boat with its motor set for 12 km/h West
How fast does the boat look like it is going from the ground?
Vector addition, X + Y = Z
7 km/h
5 km/h
12 km/h

8. Combining Velocities
Sometimes the motion of an object involves more than one velocity
Like a boat in a fast moving river:
If the river carries a current of 3 km/h East
A boat with its motor set for 4 km/h North
How fast does the boat look like it is going from the ground?
Vector addition, X + Y = Z
5 km/h
3 km/h
4 km/h