Can you tell what you see in that photo? It’s a picture of a castle drawn on one grain of sand. So it’s actually a “sand castle”! When Bedtime Math fan Jay A. asked how many grains of sand are in a sandcastle, we knew there would be a big difference between a huge sandcastle and a teeny one. So for starters, the smallest you can get is one grain. Artist Vik Muniz drew the castle on paper, then scientist Marcelo Coehlo carved it into the grain by shining a Focused Ion Beam. You can imagine how tiny this is: those lines are 1/1000th as wide as a human hair. At the other end of the scale, big sandcastles are several feet long, wide, and tall, and the number of grains is really big. If you picture a cube that’s 1 foot wide in each direction, that holds about a billion grains of sand — which will weigh between 50 and 100 pounds, depending on how wet the sand is. When we do the math, you’ll see that big sandcastles add up fast.
Wee ones: What shape does the front face of this grain of sand look like?
Little kids: If the castle here has 4 towers with teeny flags on them and 4 without, how many towers are on it in total? Bonus: If you made this same castle out of lots of sand and added 10 more towers, now how many towers would you have?
Big kids: If the base of your castle is 5 feet long by 5 feet wide and 1 foot tall, how many cubic feet of sand does that use — and about how many grains of sand? Bonus: If you then gave that sand to the world’s 7 billion people, how many grains would each person get if you gave the same to everyone, and how many would be left over?
Wee ones: A triangle.
Little kids: 8 towers. Bonus: 18 towers.
Big kids: 25 cubic feet, and 25 billion grains. Bonus: You have enough sand to give 3 grains to every person, with 4 billion grains left over.
And thank you Jay for sending us this question!