CK-12 Physical Science Concepts - For Middle School

http://www.ck12.org Chapter 4. Motion and Forces

velocity=

∆d

∆t

=

25 m−0 m

5 s−0 s

=

25 m

5 s

=5 m/s

At the following URL, review the shape of a position-time graph and its relationship to velocity. Then use the widget
at the bottom of the Web page to generate position-time graphs for an object with specified characteristics.

http://www.physicsclassroom.com/class/1DKin/Lesson-3/The-Meaning-of-Shape-for-a-p-t-Graph

Summary

• Motion can be represented by a position-time graph, which plots position relative to the starting point on the
  y-axis and time on the x-axis.


• The slope of a position-time graph represents velocity. The steeper the slope is, the faster the motion is
  changing.


• Average velocity can be calculated from a position-time graph as the change in position divided by the
  corresponding change in time.

Vocabulary

• average velocity

Explore More

Review how to calculate velocity from a position-time graph at the following URL. Then solve the two problems at
the bottom of the Web page. Be sure to check your answers and read the explanations for the correct solutions.

http://www.physicsclassroom.com/class/1dkin/u1l3c.cfm

Review

1. Describe how to make a position-time graph.


2. What is the slope of a line graph? What does the slope of a position-time graph represent?


3. Can a line on a position-time graph have a negative slope, that is, can it slope downward from left to right?
   Why or why not?


4. In Graph 1 in theFigure4.6, what is the object’s average velocity?