LAB: Reaction Time

 
   
Scenario: Let's say you are driving a car down a residential street. A cute puppy suddenly runs out from between two parked cars, right in front of your car. You are paying attention: you see the puppy immediately. In order to stop the car, however, your brain has to decide to act, send signals via your nervous system to the correct muscles, and those muscles have to move your foot to the brake pedal and press it downwards. The time it takes for all this to happen is your reaction time. In this lab, you will calculate your reaction time from simple data you collect.

Here is what you need:       

  • a meterstick or yardstick
  • a calculator
  • a helper (a sibling or parent, or fellow student)

Here is what you will do: Have your helper hold the meterstick from the end, hanging vertically. The zero end of the stick should be hanging at the bottom. Place your thumb and forefinger to either side of the stick, at the zero mark. The helper should drop the stick without warning, and you grab the stick without moving your hand vertically. Where your fingers are gripping the stick is the distance the stick fell during the time it took you to react. Record the distance in a table given below. Repeat this a total of five times. Calculate the average of your five distances. Convert the average distance to meters. Solve for t first, then plug in your average distance to calculate your average reaction time. Be careful with the units.

Turn in: in your write-up, include

  • A brief description of what you are doing. A few sentences will be sufficient.
  • Who was your helper?
  • Your data in a neat table, labeled and with units indicated.
  • Your average distance, and any unit conversions you needed to perform using the factor-label method.
  • The algebra needed to solve for time.
  • Your calculated average reaction time.
  • Solutions to the followup questions, below.
  

Followup Questions. Be sure to show your work.

1. If you are driving at a constant 60 miles per hour, how many feet will your car travel in one second?

2. How far will your car, traveling at 60 mph, move during your reaction time?

3. Measure the length of your family car. How many car lengths is your answer to Question 2?

4. Consider the scenario given at the top of the page. If the puppy was one foot further away than your answer to Question 2 when you saw it, will the puppy get smooshed or not? Explain.