At the "very top" of the ball's path, there's a tiny instant when the ball
is changing from "going up" to "going down". At that exact tiny instant,
its vertical speed is zero.
You can't go from "rising" to "falling" without passing through "zero vertical
speed", at least for an instant. It makes sense, and it feels right, but that's
not good enough in real Math. There's a big, serious, important formal law
in Calculus that says it. I think Newton may have been the one to prove it,
and it's named for him.
By the way ... it doesn't matter what the football's launch angle was,
or how hard it was kicked, or what its speed was off the punter's toe,
or how high it went, or what color it is, or who it belongs to, or even
whether it's full to the correct regulation air pressure. Its vertical speed
is still zero at the very top of its path, as it's turning around and starting
to fall.
It is in equilibrium if its velocity is not changing.
The best predictor of the radioactive nature of an isotope is the neutron-to-proton ratio of the atom. Isotopes are atoms of elements having the same number of protons however they don't have the same number of neutrons. Each isotope of an element will have different values of mass number.
A magnetic domain is a group of atoms aligns with magnetic poles. Domains are usually <span>light and dark stripes visible within each grain.</span>
