Position -time graph
1. Plot data as a position-time graph for single and multiple objects and analyze the position-time graphs.
2. Solve problems involving single and multi-particles as well as problems involving instantaneous position
When analyzing complex motion, it often is useful to represent the motion in a variety of ways. A motion diagram contains information about an object's position at various times. Tables and graphs can also show this same information.
Even though there is no data point exactly when the runner was 12.0 m beyond her starting point or where she was at t = 4.5 s, you can use the graph to estimate the time or her position.
A straight Line means Constant speed
Position (m) ® time (s)
0 ® 0
2 ® 4
4 ® 8
5 ® 10
3 ® 6
A constant speed is represented by a line in the position-time graph.
1. If the line is horizontal, the object is at rest.
2. If the line is going upwards, the object is moving at constant speed in the positive direction
3. If the line is going downwards, the object is moving at a constant speed in the negative direction
Describe the motions of person 1, person 2, and person 3 above.
person 1 is at rest
person 2 constant velocity negative direction
person 3 constant velocity positive direction
The steeper the line the faster is the object
Who is the fastest? Why
Albert, because the line is the steepest
Who is the Slowest? Why
Michael, because the line is least steep.
The position at a particular instant. Instantaneous position is usually simply called position.
Example: What is the instanteneous position of the object at 1s, 2.5s?
Multiple Objects on a Position-Time Graph
The graph to the right describes the motion of two runners moving along a straight path. The lines representing their motion are labeled A and B.
Answer the following questions
Who is faster Runner A or B? Explain why.
B is faster because the live is steeper
When and where does runner B pass runner A?
at t=45s and x=190m
How far apart were runners A and B at t = 20.0 s?
XB=60m XA=80m A was 20m in front of B