Dominoes are little toy rectangle tiles with dots on them. People like to stand them up on end in a long row, so when the first domino falls over, it knocks over the next domino, which knocks over the next…pretty soon you have a rippling wave of falling dominoes. In this simple but amazing video, Stephen Morris shows that a little domino can knock over another one that’s 1 1/2 times as big in each direction. Then that one can tip over one that ‘s 1 1/2 times as big again. In this domino chain, the first one is only 1/4 inch tall, but the 13th domino weighs more than 100 pounds! If he kept going, the 29th domino would be as tall as the Empire State Building (1,454 feet). We’d all better get out of the way!

*Wee ones:* The chain uses 13 dominoes. How many of them can you count starting from 1? Count as high as you can!

*Little kids:* If there are 13 dominoes and only the 1st has fallen, how many are left standing? *Bonus:* If the dominoes start falling, but you stop the wave by pulling out the 5th domino, how many dominoes are left standing?

*Big kids:* If each domino could tip over a domino twice as tall…how many times as tall as the 1st domino would the 5th one be? *Bonus:* If the first domino is 1 inch tall and they keep doubling, which domino would be the first one that’s taller than you are?

Answers:

*Wee ones:* 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13.

*Little kids:* 12 dominoes still standing. *Bonus:* 8 dominoes still standing.

*Big kids:* 16 times as tall, since the 2nd is twice as tall, the 3rd is 4 times as tall, and the 4th is 8 times as tall. *Bonus:* Different for everyone…compare your height to the few that are human-sized: if the 5th domino is 16 inches tall, the 6th is 32 inches (2 feet 8 inches), and the 7th is 64 inches (5 feet 4 inches). The 8th is 128 inches, more than 10 feet tall!

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