Pedagogy in Action > Library > Measurement and Uncertainty > Examples of Measurement and Uncertainty > Activity: Measure Your Reaction Time

Activity: Measure Your Reaction Time

This version written by Peter Bohacek, Henry Sibley High School; there are many versions of this lab available by other authors.
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This material was originally developed through comPADRE
as part of its collaboration with the SERC Pedagogic Service.


This is a lab activity that allows students to collect data to practice using effective measurement. While other authors have produced similar labs, this version includes uncertainty analysis consistent with effective measurement technique as presented in the module Measurement and Uncertainty.

Learning Goals

Students will have an opportunity to practice skills and solidify their understanding of effective measurement skills such as:
  • identifying sources of error
  • estimating uncertainty of individual measurements
  • estimating uncertainty of groups of measurements
  • using uncertainty propagation rules to determine the uncertainty of a calculated result
  • expressing the results of their work as a range of values, using uncertainty
  • comparing two values, both of which have uncertainty.

Context for Use

Education Level:
Grade 11 through introductory college physics.
Time required: 10-20 minutes to gather data. Students can be given class time to do calculations, or it an be assigned as homework.
Equipment: metric rulers (about 30 cm long)
Prerequisite concepts: This lab can be done early in the year before students begin intensive lab work. Students do not need to have been taught free fall or one dimensional motion.

This activity could be modified slightly and then used during a unit on free fall and one dimensional motion. The intention of this lab is to have students gather data that has some dispersion – some variation in values – so they can learn how to quantify the uncertainty of a data set and use the measurement in calculations. Strictly speaking, the variation in the reaction times represents an actual variation of their reaction time, not just a variation in the measured results. Nonetheless, this data is quick to collect, interesting to students and represents a good example of data with a variation that we can quantify.

This activity is intended to be used along with material to teach effective measurement. It includes vocabulary from and references to the Introduction to Measurement packets included in this module. Although this lab includes calculations based on kinematics of freefall, students do not need to have covered this material before doing this activity.

The sections on uncertainty and error analysis use concepts presented in the module Integrating Measurement and Uncertainty into Science Instruction

Description and Teaching Materials

Reaction Time Ruler Drop Lab Activity (Acrobat (PDF) 179kB Aug14 09)
Activity -- Measuring your reaction time (Acrobat (PDF) 179kB Aug31 09)

Teaching Notes and Tips

Data collection takes about 10-20 minutes. Students can do calculations and answer questions as homework, or in class individually or in small groups.

For additional information about this approach see How to Integrate Measurement and Uncertainty


The activity handout includes questions and calculations that can be used to assess student work.

References and Resources