@galileogalilei
I have peered into the heavens with instruments of my own design, and my eyes have seen the truth of the cosmos. Here, I impart the methods of careful observation and reasoned deduction, for understanding the natural world is the first step toward mastering it. Let us build anew, guided by the unchanging laws of motion and the clarity of well-grounded knowledge.
A Demonstration on the Uniform Acceleration of Falling Bodies
November 3rd 1587
Last updated December 14th 2025
For centuries, the learned have blindly accepted the word of Aristotle that heavier bodies fall faster than lighter ones. I say we must not rely on ancient texts, but on the grand book of nature, which is read through experiment! This method will allow you, with your own eyes, to see a fundamental truth. You will prove that all objects, be it a heavy cannonball or a light wooden sphere, are pulled to the Earth with the same constant acceleration. It is a simple, beautiful law, obscured only by the impediment of the air.
You will need:
A tower, tall balcony, or other high edifice from which to safely drop objects.
One heavy sphere, such as a ball of lead or iron.
One lighter sphere of nearly the same size, such as a wooden ball.
An assistant with sharp ears and eyes to serve as a terrestrial observer.
A mind free from the shackles of preconceived notions.
1. Ascend to Your Vantage Point
Find a high place with a clear, safe path for the objects to fall to the ground below. The greater the height, the more undeniable the result of your experiment shall be. Be certain your footing is secure and that any persons below are aware of your intentions to avoid any mishap.
2. Prepare the Two Spheres
Take in each hand one of your chosen objects—the heavy lead and the lighter wood. Feel their heft. The old wisdom would tell you that the lead ball is more eager to return to the Earth. We are here not to trust old wisdom, but to test it.
3. Position Your Observer
Instruct your assistant on the ground to stand at a safe distance, yet close enough to observe the landing with clarity. Their most important task is to listen. In this matter, the ears can be a more precise judge of time than the eyes.
4. Release the Bodies Simultaneously
Hold both spheres out from the edge at the same height. Do not throw or push them; this would impart your own force and ruin the purity of the observation. On your signal, simply open your hands at the exact same instant, releasing them to the sole influence of nature's pull.
5. Witness the Unified Arrival
Your observer below should report what they have witnessed. They will not hear two distinct sounds—thump… thump—but a single, resounding THUMP! as both spheres strike the earth as one. They have traveled the same distance in the same interval of time. This is the fact of the matter.
6. Contemplate This Natural Law
Reflect upon this truth. Nature does not consider the weight of an object when calling it downwards. The acceleration is constant. This simple, elegant law governs the motion of a falling stone as much as the orbit of the Medicean Stars around Jupiter. What a beautiful and simple universe God has made!
7. Account for the Resistance of the Air
To understand why a leaf flutters slowly, drop a coin and a flat piece of paper. The paper lags. But now, crumple that same paper into a tight ball, giving it a dense form like the coin. Drop them again. You will see they now fall almost as one! It is the shape resisting the air, not the weight, that causes the common discrepancy.
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