Study pressure and buoyancy with this Cartesian diver toy in an ordinary plastic bottle filled with water. Impress friends and family with the octopus as it dives and rises with a squeeze of the bottle. Easily slide the narrow octopus through the narrow opening of most plastic bottles. Learn and demonstrate how changes in pressure affect buoyancy in floating submerged objects. 3.5 inch X 1 inch For ages over 5. Not for children under 3 years.