Physics
Newton's Law of Universal Gravitation
Quick fact
The gravitational force between two 1-kilogram objects 1 meter apart is only about 6.67 × 10⁻¹¹ newtons—roughly the weight of a single bacterium.
Why this is interesting
You feel weight pushing you against the ground right now—but what invisible force reaches across empty space to keep the Moon circling Earth, or to hold planets in their orbits around the Sun?