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This is the video that I made during the online COVID year with all of the measurements provided. The description below details how I do this live with my classes on a "normal year" :) The PremiseThere are some amazingly precise ways to measure the speed of sound using cell phone sensors or tuning forks and harmonics, but I feel strongly that all students need the opportunity to experience the speed of sound from a low tech visual/auditory delay. Typically, I find that most students have only really experienced this delay before during thunderstorms and even then, it's not quite the same because most have never been close enough to a bolt of lightning to see and hear it simultaneously.
Measuring DistanceWhen I do this with my classes, we go out into the parking lot where there is a long straight away so that the students can stand on the one end with their stopwatches and I can stand on the other other end up by the soccer fields with the clapper while still being in their line of sight.
Measuring TimeOnce you have a distance, all you need is a time to calculate the speed of sound using the equation v = d/t. Even at a very large distance like the one shown in the map above, the time delay between the visual and auditory signals will most likely be less than a second. At this scale, one would naturally expect that the reaction time of the timers would be too large relative to the measurement to get any useful data but we can use a trick to help us out! :) Once everyone is in position, I stand in my spot with the clapper raised above my head in a "V" formation. This is the signal the students to get their stopwatches ready. Then, without warning, the I clap the boards together as fast as I can. (it is very important not to forecast the timing at all with "warm up claps" or anything else that would help them to anticipate the event) The timers will see the boards come together followed by a delayed sound of the boards clapping. Timers should start their stopwatch as soon as they see the boards clap together and stop it as soon as they hear the boards clap together. Using this method, if the visual of the boards clapping together is random and unexpected, the reaction times to start and stop the timer should offset and give fairly good results. Basically, they will be equally late in registering that they saw the clap as they will be in registering that they heard the clap but the duration of time on the timer should be the close to the actual time that they were trying for. Calculating SpeedI usually run through this clapping sequence 5-6 times so that the students have the opportunity to get 3 solid trials in. They then average these times and plug it into v = d/t along with the distance we measured together. The values aren't usually right on the money but they are usually in the 300-400 m/s range which is pretty good considering the crude nature of the experiment. In the video at the top of this post, I got ahold of a camera with a 50X zoom and was able to get some more precise time values than I was timing it in the moment but the purpose of this lab/demo is more about the experience than the result anyway so I wouldn't worry about getting too fancy. CLICK HERE FOR MORE DEMOSClick for more Waves resources ⬇ 
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Joe CossetteFather, Physics Teacher, Knowles Fellow, Friend, Techie, and Musician Blog Posts |
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