Newton's Cannon

Fire a cannonball fast enough and it never lands — it orbits

Orbit: —
7200 m/s
400 km

In Newton's Principia, he imagined firing a cannonball from a mountaintop. Too slow: it falls. At ~7.9 km/s: circular orbit. Faster: elliptical orbit. At 11.2 km/s (escape velocity = √(2GM/R)): the cannonball escapes Earth's gravity entirely.