How can I describe and illustrate motion?

If someone is running toward you or away from you, how could you find out how far away he or she is at any moment without using a meter stick or tape measure? Discuss this question with your group and write down some of your ideas.

The following motion graph of a person walking was made with a motion sensor. The person was facing away from the motion sensor. Study and discuss the motions shown in the graph with your group and then answer the questions below.

How close to the motion sensor does the student start? When does the person move forward?

• motion sensor
• meter stick or tape measure
• masking tape
• stool or table (approximately waist high)

To set up a walking track, follow the steps listed below:

• Find an open space around 1 meter wide and 5 meters long (possibly in a hallway).
• Using masking tape, mark off the straight-line distance with half-meter divisions, starting at the motion sensor.
• Place the motion sensor on a stool or table that is waist high. Align the motion sensor with the tape.

Bats fly back and forth in a cave at night to find their food. While flying at night, a bat emits squeaks that reflect off the walls of caves and flying insects. These squeaks return to the bat’s nervous system and are used as clues to determine the location and shape of the objects. The bat can tell where the next meal is and when to avoid other objects.

A motion sensor (also called an ultrasonic detector) uses technology for a similar purpose. A motion sensor uses a motion detector that sends out high frequency sound waves to a target object and waits for the sound wave to come back. The motion sensor measures the time needed for the wave to leave and return to the detector. What is so unique about a motion sensor is that software can determine and display the distance a wave covered based on the speed of sound in a graph.

Observe the following graph made by a motion sensor.

• How can you tell from the graph that the motion is repeated?
• How long does it take to repeat the motion? Write your answer below, in seconds.
• Think about the motion of a Slinky when you release one end and allow it to drop to the ground. The loose end of the Slinky drops and then bounces back. In fact, the Slinky will continue to move up and down in a repeated pattern for some time. Describe another object’s motion that might produce a wave-like repeated pattern of motion.

1. Using the prediction graph below, draw a distance-time graph that shows someone walking forward and backwards over a 4-meter track in a 30-second period of time. Label your graph to show forward (f) motion and backward (b) motion.

2. Does your prediction show a change in speed? Explain the motion in words.

3. With your back to the motion sensor, reproduce your Prediction drawing of a distance-time graph by walking forward and backwards over a 4-meter track in a 30-second period of time.

4. Using the Prediction graph above, draw a distance-time graph that shows someone walking quickly forwards for the first half of the track and then slowly for the second half. The elapsed time of the total motion should be 30 seconds. Label your graph to show when you walk quickly (q) and when you walk slowly (s).

5. With your back to the motion sensor, reproduce your Prediction drawing of a distance-time graph by walking quickly forwards for the first half of the track and then slowly for the second half.

1. How did the actual motion compare to your predictions in Collect Data 1? Explain any differences.
2. How did the actual motion compare to your predictions in Collect Data 2? Explain any differences.
3. What did you learn about motion in relationship to the movement of your body?

How does the graph display the change in position over time? How does this change in position over time relate to your speed?

• Work with your group to create a motion graph of your own using the motion sensor. You could include a change in direction, a different starting position, and different speeds. Write down the method that you used to make the graph.

• Have another group try to reproduce your graph from the written description on the same graph. Compare the graphs between the two groups.