Choose the sheet for the learner's age. Each prints on a single page. Build the project first, then fill it in together.
Ages 8-10: Predict, test & record
Name: ______________________Date: ____________
Homemade Science with Bruce Yeany · Echo Speed of Sound · Ages 8-10
Clock the Echo
Predict, clap with the echo, and record your times.
1. Predict: how long will it take the sound to reach the wall and come back?
◯ about 3 seconds◯ about 1 second◯ less than half a second
2. How far is it from you to the wall? How far does the sound travel there and back?
3. Time 10 claps. Then divide by 10 to get the time for one echo.
Try
Time for 10 claps (s)
Time for 1 echo (s)
4. When we clapped louder, the echo came back...
◯ faster◯ slower◯ in the same time
5. What did you find out? Use your numbers.
6. Why do you think timing 10 claps works better than timing just one?
Ages 11-14: Explain & design your own test
Name: ______________________Date: ____________
Homemade Science with Bruce Yeany · Echo Speed of Sound · Ages 11-14
Measuring the Speed of Sound
Use your echo data to calculate the speed of sound and judge how good your measurement is.
1. Record your data and calculate.
Trial
Round-trip distance (ft)
Average time, 1 echo (s)
Speed (ft/s)
Speed (mph)
2. Show how you changed your best speed from feet per second to miles per hour. (5,280 feet in a mile, 3,600 seconds in an hour.)
3. The real speed of sound is about 1,087 ft/s at 32 degrees F plus 1.1 ft/s for every degree warmer. Find the real speed at your temperature and your percent error.
4. Using the idea of an echo, explain why you doubled the distance to the wall.
5. List three possible sources of error in your measurement and which one you think mattered most.
6. Design a fair test of whether temperature changes the speed of sound. What would you change, measure, and keep the same?
7. Where else could you use the speed of sound? (Think about thunder and lightning.)
Answer guide for grown-ups
Homemade Science with Bruce Yeany · Echo Speed of Sound · Answer guide
Answer guide
Ages 8-10: Clock the Echo
Less than half a second (about a third of a second for a wall a few hundred feet away).
Your measured distance; the trip there and back is twice that.
Open answer: look for effort and careful observation.
In the same time. Loudness doesn't change the speed of sound.
Each echo took only a fraction of a second; sound traveled about 1,100 feet per second (about 770 mph). Answers should use the student's own numbers.
One echo is so quick that the slowness of your thumb on the stopwatch is a big part of it. Ten claps take ten times as long, so the thumb error matters much less.
Ages 11-14: Measuring the Speed of Sound
Open answer: look for effort and careful observation.
One mph = 5,280 / 3,600 = about 1.47 ft/s, so mph = (speed in ft/s) / 1.47. Example: 1,130 ft/s / 1.47 = about 769 mph.
Example at 72 degrees F: 1,087 + 1.1 x 40 = about 1,131 ft/s. Percent error = (difference / real value) x 100. Bruce's class was usually within 2-4%.
The echo is the sound reflecting off the wall, so the sound travels to the wall and back again: twice the distance.
Any three: reaction time on the stopwatch, claps not exactly on the echo, distance measured inaccurately (or uneven ground), air temperature changing along the path, wind, echoes from other buildings. Reaction time and clap timing are usually the largest.
Change: the air temperature (test on a cold day and a hot day). Measure: the time for 10 echoes and the temperature. Keep the same: the spot, the distance, the wall, the clappers, and the timing method.
Thunder: count the seconds between lightning and thunder; sound goes about 1,100 feet per second (about a mile in 5 seconds), so you can estimate how far away the storm is. Also sonar, echo sounders and measuring distances with echoes.