Isaac Newton and the “Hypotheses non Fingo”

Isaac Newton formulated the law of universal gravitation, which adequately explained the motion of all bodies in space known at his time. He also showed it is the same law that is causing everyday objects to fall on Earth.

In his famous phrase “hypothesis non fingo,” Newton stated that he did not know what causes gravity and refused to speculate. Flat-Earthers use it to discredit him. In reality, just because he did not know what causes gravity, it does not mean his law of universal gravitation is wrong.

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Curvature of Water Surface

If Earth is a sphere, why is the surface of water always flat?

Due to Earth’s gravity, water seeks the lowest potential or as close as possible to the center of Earth. It forms a practically spherical surface centered on Earth’s center. The width of the surface in everyday cases is tiny compared to Earth’s radius. Thus, the water surface looks practically flat but not perfectly flat.

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Weight and Air Density Experiment

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Using a precise digital kitchen scale and a smartphone with a pressure sensor, we can easily measure the change in weight and atmospheric pressure in different locations.

Flat-Earthers claim that an object falls down because it is denser than the air surrounding it. However, simple measurements show that things weigh less at a higher altitude where the air is less dense, contrary to the expectation if their claim is true.

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Air Density vs Object’s Weight

At a lower altitude, the air is denser, and objects weigh more. On the other hand, at a higher altitude, the air is less dense, and objects weigh less.

Flat-Earthers deny gravity and invented the “explanation” that an object falls only because it is denser than the air surrounding it. But if it were true, objects should weigh more at a higher altitude where the air is less dense. But they weigh less instead, disproving flat-Earthers’ density theory.

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Gravitational Acceleration in Archimedes’ Formula

Archimedes’ principle states that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces. Today we usually use B =  -ρgV to calculate the buoyant force, where ρ is the fluid’s density, g is the gravitational acceleration, and V is the volume of the displaced fluid.

Archimedes discovered buoyancy earlier than Newton discovered gravity, and flat-Earthers dispute the presence of g in the buoyancy formula. In reality, buoyancy depends on the weight of the fluid, and the distinction between weight and mass only occurred after Newton. Archimedes’ principle still applies, only that we now have a better understanding of what weight is.

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Isaac Newton and the Falling Apple

The fall of an apple inspired Isaac Newton to understand that the same force that brought the apple falling toward the ground also keeps the Moon in motion around Earth. However, his work involved much more than just observing the falling apple.

Flat-Earthers downplay Newton’s contribution as if it was only about the falling Apple and use the episode as a means of ridicule. In reality, Newton’s works were much more than that.

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Variation of Earth’s Gravitational Acceleration

The acceleration of free-falling objects on Earth varies. It depends on various factors. The figure of 9.8 m/s² is just a nominal value to use if the actual local value is unknown or unimportant. These variations can only be explained using the law of gravity and that the Earth is a rotating sphere.

Flat-Earthers claim that science tells us that Earth’s gravitational acceleration is always 9.8 m/s² everywhere on Earth, and they use it as “evidence” Earth is flat and stationary. But, in reality, Earth’s gravitational acceleration does indeed vary in different locations.

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What We Feel as “Weight” is the Force of Gravity

The weight of an object is the force exerted on the object by gravity. The gravitational force exerted by the Earth on an object is what we feel as the ‘weight’ of the object.

Many flat-Earthers fail to understand that the gravitational force is just another name for ‘weight’. Much misinformation in flat Earth communities arises from this misunderstanding.

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Force Vectors

Many misinformation within flat-Earth communities is present only because of their lack of understanding on how forces work on an object.

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Newton’s Cannonball

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Newton’s cannonball was a thought experiment Isaac Newton used to explain the principle of orbital motion. It was the first explanation of an orbit and still the easiest to understand.

Newton visualizes a cannon on top of a very tall mountain where the air resistance is no longer a factor. As more charge is used with each cannon shot, the speed of the cannonball will be greater, and the cannonball will hit the ground farther and farther. Finally, at a certain speed, it will not hit the ground at all. It will fall toward the spherical Earth just as fast as the Earth curves away from it. In the absence of drag from the atmosphere, it will continue forever in orbit around the Earth.

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Hill Sphere

The Moon orbits the Earth —not the Sun— because the Moon lies well within Earth’s Hill sphere. Hill sphere is the region around Earth where Earth —instead of the Sun— dominates the attraction of satellites.

Flat-Earthers noticed the Sun exerts a stronger pull to the Moon than Earth does to the Moon. They incorrectly concluded that according to science, the Moon should orbit the Sun, then proceeded to use it to discredit science. In reality, they did not account for the centrifugal acceleration resulting from the motion around the Sun, which is one of the factors that determines Earth’s Hill sphere.

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Elegance

Our understanding of gravity explains a phenomenon clearly and directly. It is one idea, easy to understand, explains so many phenomena, can account for a large amount of data, and answers many questions. In other words, we can say that gravity is elegant.

In contrast, each of the different concepts in the flat Earth model requires a separate explanation and often in conflict with each other. We can say it is ugly. It is why flat-Earthers cannot accept that a single idea of gravity can explain so many phenomena.

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“What is Gravity”

In a StarTalk episode, Neil deGrasse Tyson was given the question “what is gravity?” He quipped “we have no idea” before elaborating more. Flat-Earthers quoted it out of context to discredit Neil and gravity, completely disregarding what Neil explained afterward.

In reality, Neil did provide a very comprehensive answer to the question “what is gravity” but flat-Earthers only gave an emphasis to the “we have no idea” part of his answer, and skipped the rest of his answer.

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Pressure Difference Without a Barrier

Atmospheric pressure decreases as altitude increases. A pressure difference can occur without a barrier. Other factors, like gravity, can cause a pressure difference.

Flat-Earthers claim a pressure difference cannot possibly occur without a barrier, like Earth’s atmosphere next to the vacuum of space. In reality, it is not difficult to demonstrate that a pressure difference can exist without a barrier.

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Density Tower

A density tower is formed by layering immiscible liquids of different densities on top of each other. It is possible because Earth’s gravitational acceleration pulls denser fluid particles stronger and displace less dense ones upward.

Flat-Earthers claim that the possibility to have density towers disproves gravity. In reality, a density tower cannot form without the presence of acceleration, like Earth’s gravitational acceleration.

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Repulsive Force

Gravity does not possess repulsive force like magnetism. These are two different phenomena with different characteristics.

Flat-Earthers use the lack of a repulsive force in gravity to deny its existence. In reality, there is no requirement for an attractive force to have a repulsive force. Gravity does not act like magnetism, and the fact does not disprove gravity.

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Weightlessness, Free Fall, and Microgravity

In orbit, objects are weightless because both the objects and the spacecraft have the same speed and direction, and both are affected by the same gravitational influence. We use the spacecraft as the frame of reference. Because the objects are not in motion relative to the spacecraft, they appear to float.

In Earth orbit, the objects are still affected by Earth’s gravity, but yet they float. Flat-Earthers use it to disprove spaceflight. In reality, the objects float because we are using the spacecraft as the frame of reference, which is also moving by the same amount and is affected by the same gravity as the objects themselves.

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Richard Garriott’s “Pocket of Gravity” Magic Trick

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Richard Garriott is a video-game developer and entrepreneur who is also an avid magician. In October 2008, he flew to the ISS onboard a Soyuz rocket as a private astronaut. During his time on the ISS, he performed several magic tricks.

One of his magic tricks involves a hammer that floats and a card that seems to fall as if it is pulled down by gravity. Flat-Earthers were unaware it was a mere magic trick and wrongly assume it demonstrates things are falling in the ISS, despite other objects in the scene that float.

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Eötvös Effect: Direct Evidence Earth is a Rotating Sphere

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Eötvös effect is the change in perceived gravitational acceleration when moving eastward vs. westward. An object will weigh slightly more when moving westward than when it is stationary or moving eastward.

The slight difference in weight due to the Eötvös effect can be measured in an experiment on a flight. The Eötvös effect is direct evidence that the Earth is a rotating sphere.

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Flat-Earthers’ Alternative Facts for Gravity

Flat-Earthers reject gravity because it does not support the flat Earth model. To explain the various phenomena explained by gravity, they invented many different ‘alternative facts’ in place of gravity.

Flat-Earthers agree only on a single thing that the Earth is flat. However, as flat Earth is not fact-based, flat-Earthers cannot agree on practically everything else. Different flat-Earth denominations have their alternative explanations for gravity, all of which lacks predictive power and cannot adequately explain real-world facts.

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