Measuring Your Reaction Time

Activity #2

Measuring Your Reaction Time

CA Standard: Students know the relationship between the universal law of gravitation and the effect of gravity on an object at the surface of Earth.

Purpose: To measure the reaction times of each student member in a group using two different activities and applying the free-fall acceleration formula to solve for the time.

Materials: 1 meter stick or ruler; 1 dollar bill or any denomination bill

Introduction: Yourreaction time affects your performance in many everyday activities – from driving a car to playing sports to catching something that you drop. Reaction time is the amount of time between an event and your response to it.

Procedure:

Part A: Measuring Reaction Time with a Meter stick

1. One person in the group will hold a meter stick vertically between the thumb and index finger of the other person’s open hand. The meter stick should be held so that the zero mark is between your fingers and the 1 cm mark is above it.

2. The person catching the meter stick should not be touching the meter stick and their catching hand should not be moving in any way.

3. Without warning, release the meter stick so that it falls between the thumb and finger of the person catching the meter stick.

4. The person catching should catch the meter stick as quickly as possible.

5. Record the distance the meter stick has fallen through the catcher’s fingers.

6. Perform at least 4 trials for each person in the group. Remember to convert centimeters to meters (1 m = 100 cm). So, divide your measurements by 100 to get meters (m).

7. Switch roles and record data for the other member’s reaction time.

Use the free fall equation -

to solve for your reaction time, . The variable is obviously zero because you are releasing the meter stick from rest. So, the equation can be solved for time, yielding an answer of where is the distance the meter stick fell through your grasp and Use this equation to find time.

Part B: Measuring Reaction Time with a Dollar Bill

Hold a dollar bill so that the midpoint hangs between a friend’s fingers. Challenge your friend to catch it by snapping his or her fingers shut when you release it. Did your friend catch the bill? Switch roles.

Data and Results:

Part A: Measuring Reaction Time with a Meter stick

Student: (You) = ______

Student: (Your Partner) = ______

Part B: Measuring Reaction Time with a Dollar Bill

Student: (You) = Student: (Your Partner) =

Analysis Questions:

1. What was your average reaction time? Did you catch the ruler faster with your left hand or right hand? Why might this be so?

2. What kinds of factors affect your reaction time? Compare the two activities (Part A and B).

3. Name any possible errors you might have introduced or made during the experiment.

4. Whose reaction time was faster, you or your partners? Try to explain why.

5. Are your reaction times consistent (are they all pretty close to each other) or are there some that do not agree with the others? Explain what could account for these discrepancies or errors in your data.

6. Alcohol can slow your reaction time by as much as thirty percent. Drugs can slow your reaction time by as much as fifty percent. Tests show talking on a cell-phone while driving can slow your reaction time by as much as twenty percent. Multiply the percent (ex. 0.30, 0.50, and 0.20) by your reaction time and then add the number you get from this multiplication to your reaction time. These are your reaction times on alcohol, drugs, and on a cell phone. Do these results surprise you? How might these slowed reaction times affect your performance of daily activities?

Conclusion: