Swing That Bowling Ball

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.

Swing That Bowling Ball

September 7, 2017

Wait — why are all those bowling balls swinging on strings? They’re showing what happens when YOU ride a swing. Whether you push back a lot or a little to start, it will always take you the same amount of time to swing from back to front. Even a friend who’s bigger or smaller will take the same time as you. Try it! The only thing that changes the timing is the length of the chains. Longer swings take longer to go from front to back. In this amazing video, all those colorful bowling balls hang at slightly different heights. So even though they start swinging together, soon they separate in a ripple, clinking xylophone bars to prove it. Watch the video to see it — and hear it!

Wee ones: What shape is a bowling ball? Can you find that shape in your room?

Little kids: If 1 bowling ball swings 3 feet above the ground and another swings 4 feet above ground, which one is higher?  Bonus: If there are 14 balls between the first and last, how many are swinging in total?

Big kids: After every one of the 16 balls has made 4 full round trips (right to left and right again), how many notes have you heard them clink in total? (They clink at both the front and back.)  Bonus: If the balls play the musical notes C, D, E, F, G, A, B, then C to start the pattern again over, what note does the 16th ball play?

The sky’s the limit: If the slowest-period ball takes 5 seconds to swing from front to back, the one in the middle takes 4 seconds, and the fastest-period ball takes just 3 ½ seconds, how many seconds will it be before they all line up again on the right?

 

 

 

Answers:
Wee ones: A circle from the side, or in 3D, a “sphere.” Look for spheres of any kind in your room!

Little kids: The ball 4 feet above ground.  Bonus: 16 balls.

Big kids: 128 notes, since 4 full round trips means every ball clinks its bar 8 times.  Bonus: High D, since the first 14 cover the 1st 2 sets of 7 notes.

The sky’s the limit: At 280 seconds, or 4 minutes 40 seconds. The key here is that while 20 is a common multiple of 4 and 5, at 20 seconds the 5-second ball has done 2 full round trips and is on the right, while the 4-second ball has done only 2 ½ trips and is on the left. So they line up only every 40 seconds. For the 3 ½-second ball to meet them there, it needs to do an even number of 7-second round trips, and the smallest common multiple of 40 and 7 is 280.

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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 while still in diapers, 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. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.

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