1590, Italian physicist Galileo, who was born in Pisa, made a free-fall experiment on the leaning tower of Pisa. He dropped two spheres with different weights from the same height at the same time, and as a result, two shot puts landed at the same time, thus discovering the law of free-fall and overthrowing Aristotle's previous view that heavy objects would land first and the falling speed was directly proportional to their mass.

2. It must be outside Carter.

In his research, the German mathematician Schuhuaikate questioned a theorem in Olgilvy's Principles of Geometry: the sum of the internal angles of a triangle is equal to 180.

For more than two thousand years, people have always thought that this is a universal theorem, and scientists are more convinced of the truth of this theorem. However, Hubert's question promoted a sudden change in mathematics. German mathematician Riemann was inspired by the thought of external karting, which made the non-Euclidean set break ground.

Riemann pointed out that Euclidean geometry does not apply to all spaces. For example, on the earth sphere, the sum of the internal angles of the triangle is greater than 180.