Physics - Lab 2 - Reaction Time

Stevens High School Physics Laboratory Manual
The purpose of this lab is to determine the reaction times of your peers using kinematics.
Human reaction times vary greatly among individuals for many reasons. Fundamentally, your
reaction will be dependent on the time light takes to reach your eyes, the time it takes the nervous impulse to
reach your brain, the time your brain takes to process the visual stimulus and send a signal to your muscles, and
the time it takes for your muscles to contract. In this laboratory, you will measure how quickly you and your
classmates can catch a falling object.


Ruler (at least 30 cm long)
Paper and a writing implement
Note: Individual ‘A’ is the person whose reaction time is being tested. Individual ‘B’ is the person doing the testing.
1.
2.
3.
4.
5.
Have A face B with their thumb and forefinger open 1.0” as shown in Figure 1 below.
B should hold the ruler so that the bottom is even with the mid-point of the thumb and finger of A.
WITHOUT counting down (e.g., 1…2…3), B should drop the ruler and A should catch it immediately!
Record the ruler measurement at the midpoint of the thumb/forefinger where A caught the ruler.
Repeat steps 1-4 seven times. Repeat any obvious outliers (e.g., if A isn’t looking when B drops the
ruler, etc.).
6. Repeat steps 1-5 for all lab partners.
Figure 1: Sketch of the experimental setup showing proper gap. Note that the ruler is shown already falling.
Record your raw data in a data table, then, throw out the lowest/highest values before averaging.
Name
A. Smith
A. Ninja
Some Guy
1
4.5
1.3
8.6
2
4.7
2.1
9.5
3
1.2
0.8
11.3
Reaction Measurement (cm)
4
5
6
8.4
7.3
5.7
2.4
1.6
1.4
10.5
21.1
9.8
7
8.9
0.9
14.2
Avg.
6.1
1.5
11.1
Table 1: Raw reaction time data (in terms of distance) for three people.
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Stevens High School Physics Laboratory Manual
1. Using kinematics, calculate the ‘reaction time’, tR, based on each of the average reaction measurements
in your table. Consider that the initial velocity of the ruler was zero (Vo = 0). Also take the
thumb/forefinger to be yo = 0, and the bottom of the ruler is ‘y’ (be sure you use the proper sign). Show
your work as you would in any other problem. Equation 1 will help.
𝑦 = 𝑦0 + 𝑣0 𝑡 + 𝑎𝑡 2
(Eq. 1)
2. Next, get the list of all reaction times for your classmates. Who had the best reaction time? Can you
give any possible reasons for their quick time? How does it compare to your time?
First, measure the length of your arm and express it in meters. Consider your own reaction time as
measured in the lab. Neglecting the time that it takes light to reach your eyes (which is probably about 3 ns),
and assuming that processing speed in your brain is instantaneous, how fast do the nervous system impulses
travel from your eyes to your brain then hands? Express your answer in both meters per second and miles per
hour.
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