Think Fast!

Objective

In this experiment, you will measure the reaction time of a person by catching a metric ruler.

Introduction

Has anyone ever said, "Think fast!" and then thrown something at you? How quickly or slowly you react is called your reaction time. Your reaction time will be measured by how long it takes for your eyes to tell your brain that the ruler is falling and then for your brain to tell your fingers to catch it (Zoom, 2006). The ruler falling is called a stimulus and this type of reaction is called a simple reaction. The simple reaction time is the time it takes to react to a simple stimuli - or small change in the environment (Wikipedia contributors, 2006).

In this experiment, you will measure your reaction time by catching a metric ruler with your fingers. After you catch the ruler, you will convert your measurement in centimeters into a reaction time measured in seconds. To do this, you will need to use the following reaction time table (from Brody, 1987, 147):

Drop Distance		Reaction Time	Drop Distance		Reaction Time	Drop Distance		Reaction Time	Drop Distance		Reaction Time
(inches)	(cm)	(ms)	(inches)	(cm)	(ms)	(inches)	(cm)	(ms)	(inches)	(cm)	(ms)
1.0	2.5	72.0	7.0	17.8	190.5	13.0	33.0	259.6	19.0	48.3	313.8
2.0	5.1	101.8	8.0	20.3	203.6	14.0	35.6	269.4	20.0	50.8	322.0
3.0	7.6	124.7	9.0	22.9	216.0	15.0	38.1	278.8	21.0	53.3	329.9
4.0	10.2	144.0	10.0	25.4	227.7	16.0	40.6	288.0	22.0	55.9	337.7
5.0	12.7	161.0	11.0	27.9	238.8	17.0	43.2	296.9	23.0	58.4	345.3
6.0	15.2	176.4	12.0	30.5	249.4	18.0	45.7	305.5	24.0	61.0	352.7

To measure your reaction time, ask a friend for help. They will drop the ruler for you and you will catch it. To get better data, you should take three different measurements, each called a trial. You will combine the data from the trials together by taking an average. Then you can measure the reaction time of your friend. You will record each other's reaction times and compare them when you finish. Then you can ask other people to volunteer, too!

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• reaction time
• stimulus
• centimeters
• seconds
• trial
• average

Questions

• What is my reaction time?
• How do the reaction times of different people compare?
• How do I measure the average reaction time?

Bibliography

• The original idea for this project was sent to Zoom Science by Kelsey of Incline Village, NV:
  Zoom, 2006. "Reaction Time," Zoom Science, PBS Kids. [accessed August 4, 2006]
  http://pbskids.org/zoom/activities/sci/reactiontime.html
• Get plenty of background info on reaction times and stimuli:
  Wikipedia contributors, 2006. "Reaction time," Wikipedia, The Free Encyclopedia. [accessed August 4, 2006]
  http://en.wikipedia.org/w/index.php?title=Reaction_time&oldid=64445209
• Adair, R. K., 2002. The Physics of Baseball: Third Edition, Revised, Updated and Expanded. New York, NY: HarperCollins Publishers.
• Here is an online version of the reaction time test developed by Jim Allen:
  Allen, J., 2002. "The Online Reaction Time Test," GetYourWebsiteHere.com [accessed August 4, 2006]
  http://getyourwebsitehere.com/jswb/rttest01.html
• Brody, H., 1987. Tennis Science for Tennis Players. Philadelphia, PA: The University of Pennsylvania Press.

Materials and Equipment

• metric ruler with centimeter marks
• table and chair
• paper and pen for charting results
• a different colored sticker or pen for each person

Experimental Procedure

1. Sit in a chair with your arm resting on a table so that your wrist hangs off the edge. Your friend should hold the ruler so that it dangles above your hand. Make sure the "zero" end of the ruler is hanging between your thumb and finger.
2. When your friend lets go of the ruler, try to catch it between your thumb and finger as quickly as you can.
3. Mark the ruler where you caught it with a colored piece of tape or a sticker. This will be your first measurement, or trial #1. Write down the measurement in a data table:

   Name	Trial #1		Trial #2		Trial #3		Average Reaction Time (s)
   	ruler (cm)	time (s)	ruler (cm)	time (s)	ruler (cm)	time (s)
   Me
   Bobby
   Susie
   Mom
   Dad

4. Compare the marking on the ruler where your fingers caught it to the reaction time chart above. Write down your reaction time in the data table.
5. Repeat steps 1–4 two more times, for trial #2 and trial #3. Did your reaction times vary a lot or were they pretty much the same from trial to trial?
6. Calculate the average reaction time. Add together your three times and divide the answer by 3. Write the average reaction time in your data table.
7. Repeat steps 1–6 for your friend, and any other volunteer you would like to test.
8. Draw a bar graph to present your data. Along the left side of the graph (Y-axis) write the times from the reaction time chart. Across the bottom of the graph (X-axis) write the names of yourself and your volunteers separate columns. Draw a bar for each person up to the number that matches their average reaction time in seconds.
9. Who has the best reaction time?

Variations

• Do your reaction times improve with practice? Try doing more trials to see if our reaction time gets faster. You can see this by making a line graph of your reaction times versus trial number. Put the reaction time on the left side (Y-axis) and the trial number on the bottom (X-axis). Then place a dot above each trial for the matching reaction time. When you are done, connect the dots to make a line. Does your line slope up or down? If it slopes down, you got better! But if it slopes down, you got worse! :(
• Are older kids faster than younger kids? Try grouping volunteers by age group on your graph. Do you see any differences between groups? How about comparing you and your friends to your parents? Even try your grandparents!
• Are boys faster than girls? Group your volunteers by gender on your graph. Are there any differences? Try to get the same number of boys and girls for your comparison. Also try to get volunteers of the same age to make a fair comparison.
• Is your right hand faster than your left?
• Does your reaction time improve with both hands if you only practice with one hand?
• Many sports skills require quick reaction times: think of hitting a 95-mph fastball, returning a 100-mph tennis serve, or blocking a slapshot at the net in hockey.Try relating your reaction time to real situations in your favorite sport. For example, calculate where the baseball is on its way to the plate when the batter has to make his decision to swing. In addition to reaction time, it takes between 150–190 ms from initiating the swing to making contact with the ball. You'll also need to know the distance from the pitcher to home plate, and the speed of a pitched ball. (Adair, 2002, Chapter 3)
• For a related Science Buddies project, see: Does a Cell Phone Conversation Affect Reaction Time?

Credits

This project idea was adapted from a project by Kelsey of Incline Village, NV submitted to Zoom Science at PBS Kids:
Zoom, 2006. "Reaction Time," Zoom Science, PBS Kids. [accessed August 4, 2006]
http://pbskids.org/zoom/activities/sci/reactiontime.html

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