Direct Measurement Videos > Video Library > Keep in time

Keep in time

Summary


Nine student-musicians line up on a soccer field and clap to the beat of a metronome broadcast through a megaphone. At first view it may appear that the students farther from the metronome are not clapping in time with the metronome. However, these students are clapping when the sound of the metronome reaches their ears, delayed by the time it takes for sound to travel from the metronome.

Viewers can measure the time delay between when Emma, who is nearest the metronome, claps, and when Max, who is 80 meters away, claps. Students can use this delay to determine the speed of sound in air.


Files

Instructor Note

When teaching with this video, direct students to the student video library, which provides student access to all videos without links to instructor materials and solutions.

Three file formats are available to work with this video. For analysis, frame-by-frame viewing is needed.

DMV player of two claps in slow motion

download video of three claps in slow motion (Quicktime Video 7MB Feb15 14)

YouTube of entire video (does not allow frame-by-frame viewing)

Teaching Materials


Classroom-ready activity:

Keep in Time Activity Page

Sample questions:

  • Why don't the students appear to clap together?
  • What's the speed of sound in air?
  • What did the student at 80 m hear?
  • What did the student at 0 m hear?
  • If you graph distance vs. time for the claps what does the slope represent?
  • If you graph distance vs. time for the claps what does the Y-intercept represent?

Close

The Direct Measurement Video project has become Pivot Interactives, an educational resources company run by the same dedicated physics teachers who've been developing DMVs since in 2010. We're more committed than ever to bringing powerful teaching tools to students and instructors everywhere.

Our free service on the SERC website will come to an end on June 1, 2018. We invite you to subscribe to Pivot Interactives where you'll find new functionalities. For example, the new learning platform includes integrated, modifiable instructions, data tables with calculated columns, graphing with linear fit, and enhanced grading tools, ...not to mention a boatload of really cool new videos. This integrated platform is far more powerful and effective than videos alone. We hope that if you've had success with DMVs you'll try a free 30-day trial of the new videos and easy-to-use teacher tools.

What teachers say about Pivot Interactives:

"The new Pivot Interactives platform is an impressive leap over just having the videos only. I'll use the new PI platform in my AP Physics class more than I would use the original Direct Measurement Videos alone. " -Alan Calac, Abraham Lincoln High School. San Francisco, California

Pivot Interactives is a game changer. The price is reasonable and you can build a physics curriculum around them. The new tools in Pivot Interactives are wonderful and give more independence to the students. -Tim Taylor, Stratton Mountain School; Stratton, Vermont

"I've made it my official teaching goal this year to replace as many textbook-style homework problems as possible with Pivot exercises. Everything I see on the site is something that makes me say 'wow'. I highly recommend." -Greg Jacobs Woodberry Forest School, Woodberry Forest, VA 22989

My thoughts on Pivot Interactives in perpetuity: Take my money! -Trevor Register, Cherokee County GA

Learn more Sign up for free trial