You can make glass objects disappear.

Glass objects are visible because they reflect some of the light that shines on them and bend or refract the light that shines through them. If you eliminate reflection from and refraction by a glass object, you can make that object disappear.

Wesson™ oil. When [...]

To paraphrase the French philosopher Rene Descartes: “I sink, therefore I am.”

Squeezing the sides of a plastic soda bottle changes the fluid pressure inside. Changes influid pressure affect the buoyancy of a Cartesian diver made from an eyedropper or a Bic™ pen. The diver floats, sinks, or hovers in response to pressure changes. There [...]