10 Days of Science with Math: Reaction Time

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Today’s science with math idea is a lab exercise on Reaction Time…the time it takes our bodies to react to a stimulus. Perhaps you’ve done this before or perhaps you’ve seen similar things at a science center. Our local one has a display, but it’s computerized. This one is going to be old school. You’ll need a ruler and a data chart.

How It’s Done:

Two kids will need to work together at a time or you can be the helper. One person will be dropping the ruler and the other will be catching it. They face each other and the ruler will be held above the participant’s hands at about eye level. The participant chooses which hand will do the catching- I suggest starting with the dominant hand. He’ll be catching the ruler between his thumb and fore finger when it is released. Remember to hold the ruler so that it is dropping with the lower numbers going first.

The object is to catch the ruler and read out what number was “caught” on the ruler. If the ruler was caught and the number 4 is read on the ruler, then you record the distance on your chart. Prepare a data chart ahead of time by determining the number of trials you will do and you might want to do left and right hands to see if there is a difference.

Now if you are working with a large classroom of kids, then there’s plenty of math to go around on this one. With just a few kids in the house, you may have to get creative on finding more numbers or you can just adjust the number of times you try. It’s important to discuss what additional trials are for. Why do you want to do the experimental procedure more than once? How many is enough? What would a good scientist do? More than one go at the experiment will tell you if your results are typical or if one or another try was an outlier compared to the rest. In addition, it will tell you if your results are repeatable. When a scientist publishes a study in a journal, one of the highest compliments is whether or not the results can be replicated. In fact, a journal committee will want to know if the experiment was replicated. It greatly diminishes the work of a scientist if others cannot achieve the same results and it calls into question the reliability of the study.  So, the number of trials is important. Discuss these things as you choose how to make the data chart.

Of course, there are ways to work with data and study it to see the trends and ultimately see whether or not there are relationships between variables, etc. Today we can look at taking the average reaction time. You can also teach median and mode and do something called box and whisker plots which basically allow you to look at the range of your data and see where most of it is clustered. All of these will introduce statistics to your children.

Source Wikipedia- an example box and whisker plot plotted on a graph

If you have more than one student doing this exercise, you can use the data from all the trials of several kids to do the statistical analysis. That’s probably enough data since you are just starting out! Box and whisker plots let you look visually at the 25th and 75th percentile (the top and bottom of the box), while the middle of the box is always the median. The ends of the lines are usually the maximum and minimum values, but you can choose other parameters for them. In the example above, you can see how the plots help to see how data is distributed.

Once you’ve found these values and you look at your data, discuss with your children what trends you see. Perhaps there is a relationship between age and reaction time? Gender? Handedness?

If you have questions, please leave them in the comments! Stay tuned for another day of science with math tomorrow.


Be sure to visit these brilliant women during our 10 days adventure between November 7th-18th! I love these ladies and we know you will too.

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  1. Just had to share: This weekend I was "playing" 10 Days in the USA with my 5 year-old after the girls were finished. He says to me, "One day when I'm a man I'm really gonna' take this trip. And I'm gonna' have smoothies every day. Two every day. It's gonna' be AWESOME!"Thanks for recommending the game. ha ha

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