PART 1. Simple Visual Reaction Time (VRT)
a. Use the following procedure to collect reaction time data:
Use Safari and go to: ReactionTimer.html,
collect and write down the data in sets of 10 trials.
b. Collect fifty reaction time values for your dominant hand.
c. Collect ten reaction time values for your non-dominant hand.
d. Enter your data on an Excel Spreadsheet- remember to label
all data carefully.
e. Use the Excel procedure described at the end of the handout
to find the average value, standard deviation and SDOM of the 50 VRT in
step b (T1).
f. Repeat step e for the first ten and also for the last ten VRT
taken in step b (T2) and (T3).
g. Repeat step e for the ten VRT in step c (T4).
Your results are (with right number of
T2 (first 10) and T1 (all 50)
T2 (first 10) and T3 (last 10)
T2 (first 10 dom.) and T4 (10 non dom)
Also ask a classmate his/her value for T1 (T1') , and compare it with your T1.
i. Show a sample calculation for T2.
You should state your results as:
T = (BEST ESTIMATE) +/- (UNCERTAINTY)
BEST ESTIMATE = AVERAGE = TAV
UNCERTAINTY= SDOM (Standard Deviation of the Mean) =
PART 2. Another VRT determination
a. Have your partner release a meter stick "unexpectedly,"
vertically from rest. Position your dominant hand index and thumb fingers
about a cm apart on each side of the meter stick as close as possible to
the 0 mark. Record the positions xi
at which you grab the meter stick (which are the distances fallen by the
meterstick during your reaction time). Repeat ten times (N = 10), and then
switch roles with your partner. Find the most probable (average) value,
XAV, and the standard deviation
of your readings.
State your result for X as Best Estimate +/- Uncertainty, where:
BEST ESTIMATE = AVERAGE = XAV
UNCERTAINTY= SDOM (Standard Deviation of the Mean)
NOTE: Make sure that the number of significant figures in your
stated result is consistent with your position data.
b. Determine the value of t (=VRT) obtained from the relationship
between distance fallen x and free-fall time t:
Use the accepted value for g at Sewanee:
and state your result for t as Best Estimate +/- Uncertainty, where:
BEST ESTIMATE =
and the UNCERTAINTY =
This looks fine, but what is ε t ?
Using error propagation formulas (see ERROR
where the relative error ε is defined as ε =UNCERTAINTY/BEST ESTIMATE:
Note that in the special case (like ours) in which one error dominates ( ), then the error propagation formula simplifies to:
(notice that the factor 1/2 comes from the square root relationship between t and x)
Δt = (1/2) * (Δx/xAV) * t0
c. Compare this value for t with the value of T1 obtained
in Part 1.
Do they agree or disagree? That is, do the respective ranges of values
overlap significantly? Explain your answer very carefully.
d. What simplifying assumptions are made to be able to write Eq.
e. Imagine you are a Physics Consultant.
Which of the techniques (Part 1 or Part 2) would you recommend as a better
experimental technique to measure VRT?
Could you propose a better method?
0. Create in Column 1 a list of numbers 1-50, and in Column 2 enter your
VRT data (50 dominant, 10 non dominant).
1. Select a cell in Column 3 . Select fx in the tools bar.
Select average value. Click on next button. Use 'shift -click' to select
the first ten cells for the argument ( ) of average value. Click on finish.
2. Repeat step 1 to find the standard deviation--stdev. In the next cell,
divide this value by SQRT(N) (10 or 50 depending the case) to obtain the
SDOM (which is the uncertainty).
3. Repeat steps 1 and 2 with all 50 cells selected and then for the last
4. When you are finished select "Quit" under the File menu (command q).
6. If you want to work on the workbook again, you can
open it either by 'double-clicking' on its icon in the window or by starting
Excel and using "Open" in the File menu (command o).