Gee, I didn't know that :)

Italian astronomer and scientist Galileo Galilei (1564 - 1642) performs his legendary experiment.

Everybody "knows" that when one throws a ball, the path it takes is a parabola but that's not the case in a detailed and entertaining Forbs piece titled We All Learned Physics' Biggest Myth: That Projectiles Make A Parabola.

To whit.

Anyone who's ever taken a physics course has learned the same myth for centuries now: that any object thrown, shot, or fired in the gravitational field of Earth will trace out a parabola before striking the ground. If you neglect external forces like wind, air resistance, or any other terrestrial objects, this parabolic shape describes how the center-of-mass of your object moves extremely accurately, no matter what it is or what else is at play.

But under the laws of gravity, a parabola is an impossible shape for an object that's gravitationally bound to the Earth. The math simply doesn't work out. If we could design a precise enough experiment, we'd measure that projectiles on Earth make tiny deviations from the predicted parabolic path we all derived in class: microscopic on the scale of a human, but still significant. Instead, objects thrown on Earth trace out an elliptical orbit similar to the Moon. Here's the unexpected reason why.

If you wanted to model the gravitational field at Earth's surface, there are two simplifying assumptions you could make:

1. The Earth, at least in your vicinity, is flat rather than curved,
2. That Earth's gravitational field points straight down relative to your current location
3. The earth is a sphere.

Ergo, because the earth is round, any object traveling below escape velocity will gravitationally point directly toward the earth's center while following the curvature of the planet as per the diagram seen below, which means ... ellipses rule, not parabolas. :)

Galileo was right. :)

Gee, I didn't know that. :)