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?
A quick Google search gives the specific gravity of ketchup as 1.15 (density of 1.15 g/ml). The density of air is about 1/800 g/ml. This can be considered pretty negligible, and just be considered a volume holder, producing neutral buoyancy for the packet as a whole if the air bubble has about 15% the volume of the ketchup, or a little less than 15% of the total volume of the whole composite packet, but consider it 15% as the packet itself contributes to the weight.
As the water bottle is squeezed, say not down far enough for the water pressure to increase the 14 lb/in^2 of the normal atmosphere, if the squeeze increases the pressure to an additional 14 lb/in^2, the volume of the air bubble will halve and the volume of the packet will decrease by about 7%, decreasing its buoyancy likewise.
Perhaps the packet initially had even more than 15% the volume of the packet and had buoyancy sufficient to make it lighter than the corresponding volume of water. A little pressure would make it smaller and it would sink; let up on the pressure and it rises.
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Posted by Charlie
on 2022-03-21 10:40:47 |
ketchup
