Have you ever seen or held a helium balloon, the kind that floats straight up on its string? If you don’t hold on tight or tie it to something, it will sail away into the sky. The helium gas inside the balloon is lighter than the air around us, so the balloon floats — and it can lift stuff with it. So our friend Ana P. asked us, how many balloons would it take to lift our school principal into the air? For starters, each “liter” of helium (about 1 quart) can pick up 1 gram of mass, which is metric for 1/28th of an ounce (to compare, a candy bar is about 2 ounces). If a balloon holds, say, 3 gallons of air, that’s about 12 liters, so it can lift 12 grams. So 2 slightly bigger balloons can together pick up an ounce. Then it takes 16 times as many to pick up a whole pound — and then we need to know how many pounds your principal weighs. If you can round up enough balloons, your principal can sail into the sky to end the school year!
Wee ones: If you hold 3 balloons in your right hand and 5 balloons in your left hand, which hand is holding more? Can you hold up that hand?
Little kids: If 2 balloons can pick up 1 ounce, how many balloons do you need to pick up a 2-ounce candy bar? Bonus: If you’re blowing up balloons, and the 1st balloon is blue, the 2nd is red, the 3rd is yellow, and the 4th is blue again to repeat, how many reds do you have by the time you blow up 10 balloons?
Big kids: If 2 balloons can lift 1 ounce, how many do you need to pick up a whole pound? (Reminder: a pound has 16 ounces.) Bonus: Let’s round off and say you need 30 balloons to lift 1 pound. If your principal weighs 200 pounds, will 1,000 balloons be enough for liftoff?
Wee ones: Your left hand…raise your left hand!
Little kids: 4 balloons. Bonus: 3 reds (the 2nd, 5th, and 8th balloons).
Big kids: 32 balloons. Bonus: Not quite! You need 6,000 balloons for the principal to float.