Materials Included In Kit

Additional Materials Required

Safety Precautions

There are no special safety precautions for this activity. Follow all normal laboratory safety rules.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All materials are reusable. The activity can be reasonably completed in one 50-minute class period.

• Results will vary a great deal depending upon the individuals and the consistency used in executing the tests. It is critical that the 4-cm distance between the thumb and forefinger be maintained throughout the tests. There is a tendency to crowd the fingers together and anticipate the drop. Students should not be able to catch the card in less than 0.15 seconds. Research shows that catching it in less than 0.15 seconds is nearly impossible and is approaching the lower limit of reaction time for this task. If students are getting times less than 0.15 seconds, they are probably anticipating the drop or starting before the drop.
• A logical extension of this activity is to repeat all of the experimental conditions using other body combinations to catch the falling strip. The strip can be dropped against a wall as the extension of arm muscles is used to catch the strip between the hand and the wall. Experiment with other finger combinations. What happens if two hands are tried? Left hand versus right hand?
• Discuss real life situations where reaction times of various types can be critical and even life threatening. Reflex reactions, like feeling a hot stove, might be discussed and contrasted with coordination reaction times.
• Design experiments to determine if practice can improve reaction time.
• Individual groups’ data can be pooled and class averages can be determined. The trends revealed in such pooled data might provide more confidence in trends relative to the tasks involved in this experiment.

Introduction

How fast can you react? How long does it take from the time you sense danger until you slam on the brakes? How much variation exists among individuals and their reaction times? When does it really matter?

Concepts

• Reaction time

• Acceleration due to gravity

Background

Strength, speed, agility and reaction time are a few of the physical qualities that can play key roles in our everyday lives. Driving a car, for example, utilizes certain elements of all of these physical traits. Doing household chores, such as yard work, similarly requires elements of all of these physical attributes. Athletes are keenly aware of the fact that a little more strength, speed, agility or a faster reaction time might determine the color of the ribbon or medal awarded at the end of the competition. Reaction time is evident when a runner jumps at the sound of the starter’s gun, a boxer blocks an incoming punch or a race driver slams on the brakes to avoid a crash. Reaction time, however, should not be confused with thinking and keen anticipation. Intercepting a pass in football or smashing a tennis ball on the fly may involve more anticipation than actual quick reaction time. Certainly practice and exercise can improve speed, strength and agility. Can practice improve reaction time?

Reaction time is the amount of time it takes for a person to recognize and then respond to some signal or stimulus. The total reaction time includes the time of the reception of the signal by a body receptor, the subsequent transmission of the signal to the brain for interpretation, the transmission of a response signal from the brain to the key body parts, and the ultimate response of the body parts to the interpreted signal. Though the response may be separated some distance from the origination source, the actual time between the stimulus and the response can be extremely fast. Individuals vary in the speed at which various steps of the reaction time can occur. Coordination, physical conditioning, health and other current body conditions can play a major role in determining the total length of the reaction time to a specific stimulus.

There are many different types of reaction times. An individual with a fast reaction time for one activity may not have a fast reaction time for other activities requiring different kinds of reactions. In this laboratory activity one type of reaction time will be measured. Some individuals will have a faster reaction time than others. If other reaction time activities are conducted, different individuals will likely emerge with faster reaction times.

In this activity, the reaction time required to grab a falling object between the thumb and index finger will be measured. Since the object will fall due to gravity, the formula for acceleration due to the force of gravity can be used to calculate the precise time it has fallen and therefore, the precise reaction time.

The time it takes for an object to fall a certain distance can be found by the following equation:

where

t is the reaction time (in seconds)
d is the distance the object falls (in cm)
a is the acceleration due to gravity (980 cm/s²)

A Reaction Timer Strip is needed for this activity. Obtain your Reaction Timer Strip and notice that the 4-cm line on the Reaction Timer Strip has been marked 0.09 sec. The other distances have also been calculated and incorporated into the Reaction Timer Strip.

Materials

Safety Precautions

This laboratory activity is considered non-hazardous. Please follow all standard laboratory safety precautions.

Procedure

1. Work with a partner and take turns being the “subject” and the “experimenter.”
2. The subject should sit down with an arm resting on a table so that the hand extends beyond the edge of the table. The thumb and the forefinger should be parallel to the floor and 4 cm apart. Use the measuring side of the Reaction Timer Strip to measure the finger separation distance. The experimenter should monitor the separation distance throughout the experiment to make sure the approximate 4-cm distance is maintained for all trials. If the distance between the fingers varies too much, the results will be affected.
3. The experimenter should stand and hold the Reaction Timer Strip vertically between the thumb and forefinger of the subject so that the zero line is between the thumb and forefinger of the subject.
4. Without warning the experimenter should release the Reaction Timer Strip dropping it between the subject’s finger and thumb. The subject should catch the Reaction Timer Strip as quickly as possible using only the thumb and forefinger. The experimenter should not allow the subject to anticipate the drop! The strip should be examined to determine the spot on the strip between the subject’s fingers. Determine the time closest to the spot in the middle of the fingers. Record this time in seconds on the Reaction Time Worksheet as trial 1 on the “sight only” chart.
5. Repeat the “sight only” test four more times and record the result of each trial on the worksheet.
6. Switch the roles of the experimenter and subject and complete five trials on the new subject.
7. Calculate the average reaction time for each subject for “sight only.”
8. Repeat the entire procedure, only this time have the subject’s eyes closed when the Reaction Timer Strip is dropped. The experimenter should snap a finger, tap a pencil, or somehow signal in an audible fashion when the strip is released. Enter all the data on the worksheet in the “sound only” data chart.
9. Repeat the entire procedure once more for each subject. This time use “sight and sound.” The subject’s eyes should be open and the experimenter should use the same sound signal used in step 7.
10. Calculate the average reaction times for all three conditions and answer the questions on the worksheet.

Student Worksheet PDF

10338_Student1.pdf