Lesson 5Can You Tell The Difference?

Beth Elmore

Wizards Science

Mill Creek Middle

2011-2012

Key Terms

Control

Hypothesis

Reproducible

Sample Size

Sensitivity

Variable

Key TermControl

A standard for checking or verifying the results of an experiment. In a parallel experiment a single variable is changed. The results are compared to the control in order to see if the variable had any effect.

HypothesisA possible explanation for observations, facts, or events, that may be tested, verified, or answered by further investigation.

ReproducibleCapable of being recreated and repeated.

Sample SizeThe number of observations in a sample.

SensitivityThe degree of response of an organism or body part.

VariableThe only factor in a scientific experiment that is different from the control group.

Lesson 5 Can You Feel the Difference?

Useful scientific experiments are often designed to test only a single factor, or variable. You may remember that Dr. Goldberger had screens put on the windows during his experiment on prisoners. He also had bed sheets and clothes washed regularly. One strength of Dr. Goldberger’s experiment was his effort to reduce all the other variables—such as the presence of insects or variations in cleanliness—that could affect his results. His goal was to make diet the only factor that was being changed. In this case, diet was the variable being tested.

Scientists are interested in how people respond to the environment. People use their senses—touch, sight, hearing, smell, and taste—to get information about their surroundings. This information travels through nerves to the human brain. In this activity you will investigate your sense of touch.

Can you identify all of the variables that might affect your results? What can you do to try to keep all of these variables the same? How can you control those variables to measure the smallest distance apart at which you can feel two points?

Challenge - What is the smallest distance apart at which you can still feel two points? How do you compare with other people in your class?

Materials

For each pair of students1 2-point sensor

6 plastic toothpicks

1 Student Sheet 5.1, “Touch-test Data”

1 Student Sheet 5.2, “Sensitivity to Two Points: Class Results”

Student Sheet 1.1 “Anticipation Guide: Ideas about Experimental

Design,” from Activity 1

SafetyBe careful when doing the touch tests. Press gently when testing, making sure to only slightly depress the skin surface.

Procedure: Part A

1. Slide 2 plastic toothpicks into the 2-point sensor on the side marked “1.5 cm.”

2. With your eyes open, investigate your sense of touch by touching the skin of your fingers, palm of your hand, and forearm with the point of just one toothpick.

Procedure: Part A

3. With your eyes open, touch your fingers, palm, and forearm with the points of both toothpicks. Notice what the points look like as they touch your skin and compare that to how it feels.

4. Record your observations in your science notebook while your partner investigates his or her own sense of touch.

Procedure: Part A

5. Have your partner close his or her eyes while you touch the skin on his or her fingers with either one or two toothpick points. Touch just hard enough to see that the points are barely pushing down on the skin. Randomly alternate between one and two points. Can your partner tell the difference?

6. Create a larger version of the table shown on the next page. In the table, record your observations about your partner’s ability to tell the difference between one and two points on his or her fingers.

Table 1: Touch-test Data

Person being tested Fingers Palm Forearm

Name:

Name:

7. Repeat Steps 5 and 6 on yourpartner’s palm and forearm.

8. Switch places and repeatSteps 5–7.

9. Discuss with your partner what you observe when you are lightly touching your partner’s skin with the one or two-point sensor. What does the skin look like when you lightly touch it with the sensor? How far is the skin depressed?

10. Discuss with your partner the variables that were easy to control and the variables that were harder to control. List these in your science notebook. Discuss how you will control the more difficult variables in Part B of the activity.

Part B11. What is the smallest distance—0.7 cm, 1.5 cm, or 2.0 cm—at which you think you can still feel two points on the palm of your hand? In your science notebook, record your hypothesis. Explain why you made this prediction.

12. Identify your dominant hand. (This is usually the hand you write with.) Throughout the experiment, you will test your dominant hand.

13. Begin completing Student Sheet 5.1, “Touch-test Data.” Write your name, and circle which of your hands is dominant. You will begin by testing the palm of your hand, so circle “palm” as the part tested.

14. Since you will test your partner (and vice versa), switch student sheets so you can record the data on his or her sheet.

15. Slide two toothpicks into each side of the 2-point sensor as shown on the left. You should end up with toothpicks on three sides, with the toothpick points 0.7 cm apart, 1.5 cm apart, and 2.0 cm apart.

16. Practice using the 2-point sensor so that you can safely and easily test using any of the three sides.

Part B17. As the experimenter, you will use the 2-point sensor to test your partner. Record your partner’s responses on Table 1, “Touch-test Data,” on Student Sheet 5.1. It is important that you fill in each box in each row before starting the next row. For example, when you do Trial 1, you will fill in each box in the first row:

a. Turn the 2-point sensor to the 0.7 cm side and touch your partner’s palm with just one point.

b. Turn the sensor to the 1.5 cm side and touch your partner’s palm with just one point.

c. Turn the sensor to 2.0 cm and touch your partner’s palm with two points.

Part B18. Before starting the touch tests, ask your partner to close his or her eyes. The partner being tested should not try to “guess the right answer.” The goal is to report what you really feel—one point or two.

19. Use Table 1, “Touch-test Data,” to test your partner. You can start with any row you want, but be sure you complete all the rows. Don’t tell your partner which row you are using. Remember to touch just hard enough to see that the points are barely pushing down on the skin. After each touch test, have your partner report whether he or she feels one or two points, and record the response.

20. After you complete all the touch tests in Table 1, have your partner test you by repeating Steps 17-19.

21. Give your partner back his or her original Student Sheet.

22. Complete the rest of Student Sheet 5.1.

22. If you have time, repeat this experiment to test the sensitivity of your fingertips and your forearm.

End of Lesson