Physics
Newton's Law of Universal Gravitation
Quick fact
Newton formulated this law in the 1680s, but it took another century for the gravitational constant G to be measured. The force is incredibly weak — even between you and this screen, a tiny attraction exists, though far too small to feel.
Why this is interesting
Why does an apple fall straight down, yet the Moon seems to defy gravity by staying in the sky? The answer lies in one simple, universal rule that connects them both.