I placed a ketchup packet into a plastic bottle and filled with water almost to the top then replaced the cap. The packet barely floated then I squeezed the bottle and the packet fell when I stopped squeezing the bottle the packet came back up.
Before squeezing the bottle, the packet floated because it is less dense than the water. When I squeeze the bottle, the water becomes denser than the packet, causing the packet to sink. This happens because of the concept that things denser than water will sink and things not as dense as water will float. In addition, compressed air is denser than water therefore, when squeezing the bottle the packet becomes less dense also and will sink.
An additional solution is, air is compressible and water is not. When the bottle is squeezed, it causes the air to be compressed as a result the packet sinks.
When releasing the squeeze on the bottle the air is no longer compressed and the packet will float again.
Another solution is the buoyancy of the packet. The concept of just enough buoyancy will make the packet barely float and when the buoyancy of the packet is reduced, the packet sinks. This happens because the packet has just the right buoyancy to float in the bottle of water until the bottle is squeezed. By squeezing the bottle, it reduces the buoyancy of the packet and causes it to sink. By releasing, the pressure applied to the bottle the packet returns to the buoyancy that is just right for packet to barely float in the bottle.
The first time I attempted the puzzler my packet did not float. Once I added more water, the packet floated just above the bottom of the surface. This made the buoyancy of the packet perfect...