Can you tell exactly how far someone is away from you without using a meter stick or tape measure? How would you do this? If someone is running toward you or away from you, how could you find out how far way he or she is at any moment? Discuss these questions with your group and write down some of your ideas to share with the class.

Long distance runners vary their speed when the run a race. How could you determine how fast they were going at different points in the race? Discuss this question with your group and write down some of your ideas to share with the class.

You've had some experience using a sonar ranger represent different kinds of motion one kind of graph that shows changes over time, a distance-time graph. You can use also use a sonar ranger to collect data about people moving.

Remember that a sonar ranger uses a motion detector that sends out high frequency sound waves to a target object and waits for it to come back. The sonar ranger measures the time needed for the wave to leave and return to the detector. The software determines and displays the distance the pulse covered based on the speed of sound.

The following motion graph of a person walking was made with a sonar ranger. Discuss the motions shown with your group. When does the person move forward? How close to the sonar ranger did the student start? Did the student change speeds?

Try it out for yourself with the sonar ranger! Go to the "Investigation" to find out how.