1. Constant, average and Instantaneous Velocity
Position-Time and Velocity-Time
Graphs

2. Motion Uniform motion Non-uniform motion
Velocity (rate of change of position) remain constant
Non-uniform motion
Velocity is changing (in magnitude, direction or both

3. Average Velocity
When calculating average velocity only the final and initial velocity are considered. One is not sure what has occurred in between these data points

4. Constant Velocity
When calculating the constant velocity of an object all changes during the time interval are considered.
The data points are organized into a table and a position-time graph is plotted

5. Average Velocity vrs. Constant Velocity
Open text to page 49 and compare figure 2.13 and 2.14
Pre-lab – page 50 (to do on Thursday)
Web site exercise – PT graphs

6. Position-Time Graphs Position on y axis Time on x axis
Slope = velocity (steeper the line, higher the velocity
Change of direction (moving towards zero)
Velocity = zero (horizontal line)

7. Instantaneous Velocity
The velocity at a specific point in time. It is the slope of a tangent to the curve of a PT graph
Model problem (page 55)
Do questions 4 and 5 page 57
Do questions 1-3, 5 and 6 page 60

8. Acceleration
A vector quantity that describes the rate of change in velocity
The quotient of change in velocity and the time interval over which the change takes place
a = Δv/t
v – velocity (m/s)
t – time (s)
a – acceleration (m/s/s or m/s2)

9. Example: Truck v = 20 m/s [E] a= 1.5 m/s2 [E] Start finish
V= 20 m/s [E] m/s [E] 23 m/s [E]
T= 0s s s

10. An object can accelerate without either speeding up or slowing down…
The direction of the acceleration vector is the direction of the change in velocity and not the direction of the velocity itself
See figures on page 62
Increase velocity (pos. acceleration)
Decrease velocity (neg. acceleration)
An object can accelerate without either speeding up or slowing down…

11. If the magnitude of the velocity does not change but the direction does, the object is accelerating

12. Uniform vrs. Non-Uniform Acceleration
Velocity
v=Δd/t
slope on a PT graph
with curving graph use a tangent to find instantaneous velocity
can be constant or non-uniform
Acceleration
a = Δv/t
slope on a VT graph
with curving graph use a tangent to find instantaneous velocity
can be constant or non-uniform

13. Notice that we use the terms constant, average and instantaneous acceleration
Check out fig on page 64