Three important notes on position-time graphs:

- The y-axis represents position.
- The x-axis represents time.
- The slope of the graph represents velocity.
- If the position is in , then a positive slope means the velocity is . If the slope is negative then the velocity is .

## Examples: Day 2, Position-Time Graphs

- Peter Parker is on his way to school when he notices the bus is about to leave. He runs to catch it, below is a graph of his movement.

- Determine the average velocity of the object in the graph above for the first four seconds.
- Determine the average velocity of the object in the graph above for the full ten second time interval.

Since the graph is a line, the slope is constant. Therefore, velocity will still be 2 m/s [N].

- Describe Peter’s motion based on the graph.

Peter runs at a constant velocity of 2 m/s North.

- Determine the average velocity of the object in the graph above for the first four seconds.
- Later, Spider-Man launches off the top of a building in downtown Manhattan. The graph of his movement is below.

- At what time is Spider-Man travelling the fastest?

At the beginning of his fall, near 0 s.

- At what time is he travelling the slowest?

At the end of his fall, near 10 s.

- Estimate his velocity at 10 s.

Spider-Man’s velocity at 10 s is just above 0 m/s [down].

- Estimate his velocity at 2 s.

Spider-Man’s velocity at 2 s is approximately 1.5 m/s [down].

- Determine his average velocity between 0 and 10 s.

Determining Spider-Man’s average velocity means drawing a secant of the graph from 0 s to 10 s and then finding the slope of that graph. - Describe his motion.

Spider-Man falls down off the building, quickly at first but slowing to a stop.

- At what time is Spider-Man travelling the fastest?
- Consider the following situation:
- Peter begins by riding his bicycle down the street travelling at 30 m [E] in 4.0 s.
- He notices police cars zooming down the same street in the other direction, so he stops abruptly for 15 seconds to change into his Spidey costume.
- He then races West, travelling 60 m in 6.0 seconds.

- Sketch his motion.

- Determine his overall distance traveled.

Peter travels a total of 90 m.

- Determine his overall displacement.

His displacement is 30 m [W].

- Determine his overall time.

Peter travels for a total of 25 s.

- Determine his average speed.
- Determine his average velocity.

## Practice

Fundamentals of Physics:

- Pg. 15, #1-4

## Related Assignments

- Assignment E
- CBR Lab

- Assignment F
- Pg. 4, 5 (handout)

- Assignment G
- Pg. 8, 9 (handout)

- Assignment H
- Pg. 30, # 12

- Assignment I
- Pg. 33, #28, 29

- Assignment J
- Pg. 35, #43, 44