Did you know that you lose weight overnight? Sure, when you run or jump around or do other exercise, you lose weight because you burn off fat. But what’s going on in your sleep? You lose weight because you lose water. Every time you breathe out, you lose water vapor, as lots of teeny tiny droplets. You also sweat out some water through your skin. Water is heavy: a cup of water weighs 1/2 pound. If you weigh yourself right before bed (after peeing) and again when you wake up (before peeing in the morning), you’ll see that you lost weight! Grown-ups can lose more than a pound just lying there. Try weighing yourself before and after sleeping, and see what you find out!
Wee ones: Put a small amount of water in a cup, and drink it as you count your gulps. Now try putting about twice as much water, and count again taking the same size gulps. Did you take more gulps?
Little kids: If 2 cups of water weigh 1 pound, how much do 4 cups of water weigh? Bonus: How much do you weigh in pounds? If you then drink 1 pound of water, how much do you weigh on the scale afterwards?
Big kids: If you let out a breath every 5 seconds while sleeping, how many times do you breathe out in 1 minute? Count up by 5s if it helps! (Reminder: A minute has 60 seconds.) Bonus: Then how many times do you breathe out in 1 hour? (An hour has 60 minutes…and multiplying by 60 is like multiplying by 2 x 3 x 10.)
The sky’s the limit: And now…if you sleep 8 hours, how many times do you breathe out water overnight? (A trick if needed: 8 is 2 x 2 x 2, so to multiply a number by 8 you can double the number, then double it again, then double it again.)
Wee ones: See how many gulps you get each time!
Little kids: 2 pounds. Bonus: Different for everyone…find your weight in pounds, then add 1.
Big kids: 12 times. Bonus: 720 times.
The sky’s the limit: 5,760 times!
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.