Mile-Long Xylophone

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Mile-Long Xylophone

April 2, 2019

Well, we’re not sure it’s a full mile, but it could be the world’s longest xylophone. In this videoย (which is actually an ad for a cellphone), we see and hear a ball roll down a really long row of wooden steps. The steps are actually bars of all different lengths, so as the ball hits each one, it makes a cute plinking musical note, just like a mallet hitting a xylophone. So the ball plays a whole song, a famous grown-up piece called “Jesu, Joy of Man’s Desiring”. Think of all the work to cut hundreds of pieces of wood the right length, line them up in order, and then nail them to the ramp. It takes homemade musical instruments to a whole new level.

Wee ones: Shorter bars play higher notes than longer bars. Which one plays a higher note, a 6-inch bar or an 8-inch bar?

Little kids: The ball knocks other balls down tunnels of smaller bars to play faster notes. If a tunnel has 2 sets of 10 wooden bars, how many bars is that? Bonus: If all the tunnels have 20 bars and 3 balls each do this trick, how many notes do those 3 balls play altogether?

Big kids: The ball plays about 3 notes each second. How many does it play in 1 minute? (Reminder: A minute has 60 seconds.) Bonus: How many notes does it play over the 2 minutes and 2 seconds, assuming all the same quick notes?

The sky’s the limit: If each regular step brings the ball 6 inches forward and takes 1/3 of a second, how far does the ball travel in a 2-minute song?











Wee ones: The 6-inch bar is shorter, so it plays the higher note.

Little kids: 20 bars. Bonus: 60 notes.

Big kids: 180 notes. Bonus: 366 notes, since it’s 360 plus 2 more sets of 3 notes.

The sky’s the limit: 180 feet. The ball travels 1 1/2 feet each second (3 x 1/2), and 2 minutes have 120 seconds (2 x 60). 1/2 of 120 is 60, so 1 1/2 of 120 is 120+60=180.

And thank you Catherine M. for sharing this amazing video!

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About the Author

Laura Overdeck

Laura Overdeck

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Lauraโ€™s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.

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