9781422284995

“We learned about this last year in physics class,” Mei explained. “It has to do with buoyancy .” “What?” Mei explained, “Buoyant forces are sort of like gravity.

buoyancy the upward force put on an object that is immersed in liquid; the force is equal to the mass of the object Words to Understand

Gravity pulls everything down toward Earth, right? Water, and other fluids actually exert their own force—a buoyant force. It’s an upward force on an object. It acts in the opposite direction of gravity, making things feel lighter.” Hayato caught on, “Which is why I feel lighter in the pool!” “Exactly.” Just then the flight attendant came around with the drink cart. “May I please have a cup of water with no ice?” Mei asked. “Thank you.” Mei reached into her carry-on bag and pulled out an empty pill bottle. She placed five pen- nies inside. She turned to her brother and said, “What do you think will happen when I drop this into the cup of water?” “Duh . . . it’ll sink.” “Alright. Let’s see.” She dropped it in and the bottle sank. Some of the water spilled over the top of the cup. Mei cleaned up the spilt water with a napkin and took the pennies out of the canister. She

refilled the cup of water to its original level. She held up the empty canister and said, “What if I put this in?” Hayato looked less sure this time. “I think it will . . . float?” “Let’s see.” She dropped the empty canister into the cup. It floated with just part of it under water. Some water spilled over the top, but not as much as before. Mei cleaned up the mess again. “Ta-dah! Did you see it?” “See what?” “I just showed you how a boat floats! That was Archimedes’ principle at work. He was an ancient Greek mathematician who came up with formulas and ideas on how to explain things.”

13