A pendulum goes to and fro in the same amount of time regardless of how big the swings are – only when the swings are small.
Although he bragged of having designed one, Galileo never made a pendulum clock. His son did after Galileo died.
In 1925, Einstein predicted a very unusual phase transition that occurs for the quantum ideal gas. Einstein describes the phenomenon in a letter to Paul Ehrenfest (1880–1933):
“From a certain temperature on, the molecules ‘condense’ without attractive forces, that is, they accumulate at zero velocity.”
In other words, as the temperature is lowered, the atoms in the gas begin to “pile up” or condense into the lowest (single particle) energy state, which is the one with zero kinetic energy; there’s a critical temperature whereby a phase transition (now called (Bose-Einstein condensation) occurs. This effect becomes most pronounced as the temperature is lowered to absolute zero, at which point, all the gas atoms condense into this lowest energy state. This phenomenon is an example of quantum entanglement.
Hints of energy being conserved, much like momentum, were showing up by the 1840s. But unlike momentum conservation, which by comparison was quickly accepted and understood (pretty much by 1687 with Newton’s Principia), energy conservation remained a mystery until 1850.
In 1798, while boring holes into cannon barrels (as part of the manufacturing process), Count Rumford concluded that heat was the result of some sort of motion within objects.
In 1644, in his Principles of Philosophy, René Descartes (1596-1650) proposed that the total motion of the universe is conserved. While this conservation of motion concept bears a certain similarity with Newton’s conservation of momentum, it’s still wrong.
An object in free fall was too fast for Galileo to accurately measure, so he focused on the slower motion down an inclined plane.
Proposed in 1811, Avogadro’s Hypothesis only began to gain acceptance in 1858 (two years after his death) thanks to Stanislao Cannizzaro.
Einstein‘s doctoral thesis was entitled: On A New Determination of Molecular Dimensions. Extensions of this effort lead to his famous paper on Brownian motion in 1905, which helped to solidified the existence of atoms.
In 1909, Jean Baptiste Perrin provided the first accurate experimental determination of Avogadro’s number.
