Day 160: Determining the Speed of Sound

The AP Economics exam threw a wrench in my original plan for College-Prep Physics today. So we decided to enjoy the nice weather and go outside to determine the speed of sound.

In the video, Ryan is clapping wood blocks together at a rate of 2 claps per second (1/2 second per clap). Sophie is holding a digital metronome to help Ryan keep pace. As Ryan backs up, the sound of the clapping and the sight of the clapping will slowly fall out of step. When the sound of the claps is exactly out of sync with the sight of the claps (ie, we hear the sound when the blocks are furthest apart), we know that it took the sound 1/4 second to reach us. The we measure the distance between Ryan and us, and calculate the speed of sound.

Distance = 84 meters, so Speed = 336 m/s. Based on the air temperature outside, the speed of sound should be approximately 340 m/s. Not bad!

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About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

One response to “Day 160: Determining the Speed of Sound”

  1. Greg says :

    Our department doesn’t have a digital metronome, but all of my students have smartphones & earphones. So I made a half-second metronome youtube "video" the block-clapper can listen to in order to keep the beat:http://www.youtube.com/watch?v=WC_wDnr1eWs

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