Jason picked up a plastic water bottle and filled it to the rim with water. He put a ketchup sachet in it and closed it up.
Jason approached his girlfriend Lola and said, "If you can solve how this works, I will give you a dollar."
Jason said, "down" and the sachet of ketchup suddenly went down. Then he said, "up" and it went up. Then he said, "down", and when it was halfway down, he said, "stay" and it stayed.
How did Jason manage to do this?
This is a
"Cartesian Diver" and has an extensive literature online. I have made hundreds for school kids to take home and amaze their families with. Squeezing on the bottle compresses the air in the sachet, lowering its volume and thus raising its density above 1 g/cc, thereby causing it to sink. Releasing the squeeze reverses the process. The diver is quite controllable. (The water in the bottle and in the sachet are of course incompressible.)
A great trick is to tell a kid they have a magnetic finger, and have them watch the diver go up and down following their pointed finger while you subtly squeeze. But, some other kids are just not magnetic!
Edited on March 21, 2022, 10:25 am
soln
