## Free Fall

Objects fall down because of gravity. Flat-Earthers deny gravity & wrongly claim they fall down because of density. For a demonstration, we can ask any flat-Earthers the following simple physics problem:

“A rigid object is released at the height h above the ground, what is the object’s velocity right before it hits the ground?”

Flat-Earthers will not be able to solve this free-fall problem without using the gravitational acceleration g=9.8 m/s². Some will call it by a different name, showing that it is just a “branding” problem. Practically all the time, they will not involve density to solve it, if they can solve it at all.

## Assumption for Simplification in Scientific Models

When creating scientific models of complex phenomena, we simplify things by reducing them to as simple a form as possible to make the calculations more feasible and less complex. Common simplifications include assuming objects as spheres, things exist in a vacuum, frictionless pulleys, massless ropes, and a flat Earth.

Flat-Earthers noticed that some scientific journals use a flat Earth in their models, and they use it as “evidence” the authors knew Earth is flat. In reality, it is just an assumption used in the models to simplify the calculation. It does not imply the Earth is flat.

## Uniform Circular Motion

The motion of a specific location on Earth due to Earth’s rotation is a uniform circular motion. We can separate it into a uniform linear motion and a centripetal acceleration toward Earth’s center. From the reference frame of an observer on Earth, the latter results in a constant centrifugal acceleration, which is felt simultaneously with Earth’s gravitational acceleration.

We often use the uniform linear motion of everyday objects to explain the effect (or the lack of thereof) of uniform motion of Earth’s rotation. Flat-Earthers incorrectly reject it just because “it is not a circular motion unlike Earth’s rotation” In reality, a uniform linear motion is one component of a uniform circular motion. And these explanations are correct and still apply.

## Classical vs Modern Physics

Classical physics —like Newton’s law of motion, and Newton’s law of universal gravitation— has been superseded by Special Relativity, General Relativity, and Quantum Mechanics. But it doesn’t mean classical physics is wrong. Classical physics is still applicable when the parameters approach common, terrestrial values we use every day.

Pseudoscientists —including flat-Earthers— often misunderstood this and take the fact that classical physics is still being taught in schools as ‘proof’ of deception and the failure of modern science to explain the world. They are wrong.