AP PHYSICS 1
Name ___________________
Lab: Reaction Time – Responding to Road Hazards
Purpose:
1. Measure reaction time
2. Investigate how distractions affect reaction time
3. To calculate reaction time
What do you see?
Take a look Picture at the right
Many deaths that occur on the highway result from the
inability of a driver to respond in time to hazard on the road.
Prelab: What do you think?
What factors affect the time you need to react to an emergency
situation while driving?
Procedure:
You can never react instantaneously to any situation. The fastest reaction that you have is
to pain. For instance, the involuntary reaction to heat is very fast, but not instantaneous because it
requires time for the signal to be sent to the brain, for the brain to process the information (i.e.
HOT!), for the signal to be relayed back to the appendage, and for the reaction to occur. Conscious
choices for movements take even longer.
We will measure your average reaction time taking advantage of gravity. Hold
your index finger and thumb about one inch apart. Have a member of your lab group
hold a meter stick vertically with the end just between your fingertips. The lab
partner will release the meter stick randomly and you need to pinch your
index/middle and thumb together to catch the stick.
 Record the distance that the stick has dropped by measuring the
distance from the bottom of the stick to where the fingers are.
 Repeat this exercise at least 3 times and average the distances together for each group
member.
Use your knowledge of falling bodies to calculate the time that the meter stick was falling (your
reaction time). Use the fact that the acceleration due to gravity is known to be 9.8 m/s 2 in your
calculation. Be sure to show all these calculations in your lab report.
Trial
1
2
3
position
released
(cm)
position
caught
(cm)
displacement
(m)
reaction
time
[sec]
Average
reaction
time
AP PHYSICS 1
Name ___________________
1. You are able to find your reaction time by dropping a ruler and use right equation.
Record your answer on your data table. Show your work and what equation you used on
separate piece of paper.
2. Based on your average reaction time, how far would you travel (in meters) in a car that
was moving at a constant 40 mph (1 mph equals 0.45 m/sec) while you reacted to a
sudden change in a traffic situation? Show your work!
Your average reaction time was The distance the car would travel Reaction time with Distractions:
1. Before your partner dropped ruler, you already knew what you were supposed to do upon
receiving that signal. Suppose you had to make a decision after the ruler drop. Repeat the
ruler-catching experiment while being distracted by a decision you have to make. Use the
following rule to do this experiment.
Rule: the student dropping the ruler now says either “RED” at the moment the ruler is
dropped, which means you should catch the ruler, or “GREEN” which means you should
let the ruler drop.
2. Suppose you are talking on a cellphone or changing a CD while driving. How do these
distractions affect your reaction time? To find out, repeat the ruler drop with one hand
(using the “red” and “green” cues), while at the same time you do one of the following
a. Pretend to change a CD with your other hand
b. Simulate dialing a phone number by entering the phone number on your calculator.
3. You will calculate average of five reaction times. Make another Data Table with
distraction on separate piece of paper!
4. Write your conclusion after comparing your average reaction time with the distraction to
your average reaction time without the distraction. (a paragraph)
5. Make a list of 10 activities that could distract you from driving safety.