Vanadium is my favourite element because valadium alloys are used in nuclear reactors, valdium is also used for some ceramics and glass, its essential to some species (including humans although we need very little) an example of this is valafium is used to treat diabetes and low blood sugar
Speed of light
According to Einstein, the speed of light is constant in all points of reference. In addition, he pointed out the speed of light is the maximum speed known since in practice one can never catch up with the beam of light. This is explained by his theory of relativity.
Density applies to many if not all aspects of life. With density you can explain why ice floats. You can explain why oxygen is on the earth, and not floating around in space( or being replaced by another gas). You can also explain why heat rises while cold air sinks.
