Flat-Earthers reject gravity. They use various excuses to discredit the Cavendish experiment, an important experiment about gravity.
A weighing scale measures mass by measuring the gravitational force exerted by the object we measure. Because the magnitude of the force depends on the strength of the gravitational acceleration, the result can vary depending on the location. It is the reason the scale needs to be calibrated after it is moved to another location.
On the other hand, a balance measures mass by comparing the object’s mass to a previously known mass. Because both masses are affected by the same gravitational acceleration, a balance is not affected by the change in gravitational acceleration.
Tides are caused by the difference in the strength and direction of lunar and solar gravity received by the different locations on Earth.
Much flat-Earth misinformation about tides arises from the wrong assumption that tides are caused by the strength of lunar gravity received by a specific location alone. In reality, tides are caused by the gradual change in the moon’s gravity over the entire Earth.
A zero-gravity aircraft flies in a parabolic motion following a free-fall motion to provide a brief weightless environment.
Flat-Earthers claim videos of astronauts in space were faked in zero-gravity aircraft. In reality, a zero-gravity plane can only provide ~25 seconds of continuous weightlessness and cannot be used to film long-take videos in a weightless condition.
Earth pulls all objects downward by the same gravitational acceleration of 9.8 m/s². But the force of gravity exerted by Earth on an object still depends on its mass. An object with a greater mass has a greater force of gravity (also called weight).
Flat-Earthers claim that if greater mass means a greater force of gravity, a bowling ball in a vacuum should fall faster than a feather. In reality, they confuse acceleration with force. Both fall at the same speed because the gravitational acceleration is the same on both, but their forces of gravity are different.
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.
Ocean tides occur because the water flows from locations with a low tide to those with a high tide on the other side of the world. On the other hand, the world’s lakes are not interconnected, & therefore, no significant tides can occur.
Tides are much smaller in lakes, and flat-Earthers use them to discredit gravity. In reality, lakes are not connected. Water in a lake cannot flow to another on the other side of Earth and cannot cause a low tide to one & high tide to another.
Archimedes’ principle states that any object, totally or partially immersed in a fluid, is buoyed up by force equal to the weight of the fluid displaced by the object. Meanwhile, Newton’s law of universal gravitation states that every particle attracts each other with force directly proportional to their masses & inversely proportional to the square of their distances.
Flat-Earthers like to characterize gravity as if it was “invented” to “replace” Archimedes’ principle & that the two are competing theories. In reality, these are two different theories that explain different phenomena. Gravity does not explain anything that Archimedes’ principle explains and vice versa. Gravity does not replace Archimedes’ principle; both are valid and in use today.
Gravity is not the only force. Other forms of force exist. Multiple forces can affect an object at the same time. Forces can counteract gravity, making an object move against the direction of gravity. These cases do not disprove gravity.
Objects can move against the direction of gravity, and flat-Earthers use it as “evidence” that gravity does not exist. In reality, there is at least a force other than gravity affecting the object, in the opposite direction from gravity, with a larger magnitude. Continue reading “Countering Gravity”
The Cavendish experiment was the first experiment to measure gravity between masses in the laboratory. The experiment has been repeated numerous times over two centuries with consistent results. Many other types of experiments also confirmed it.
Flat-Earthers incorrectly claim the Cavendish experiment has never been reproduced. They focus solely on the original experiment to discredit it. In reality, there are far too many repeats of the experiment. To discredit the experiment, they have to address all and each of the repeats of the experiment.
If gravity is the attraction between masses, then why two hanging masses do not appear attracted to each other? Because there is a really huge mass (the Earth) below both masses, attracting both masses with a much significantly larger force compared to that between each other.
The Schiehallion experiment used a massive mountain as one of the masses. And they were able to measure the effect, called the vertical deflection.
The Cavendish experiment controls the vertical attraction from Earth out of the equation. Therefore, we can observe and measure the weak and slow horizontal attraction between the masses, without interference from Earth.
The NCSE is an organization to educate the public & the press about evolution & climate change. They wrote a satirical article, “Gravity: It’s Only a Theory,” to demonstrate what might happen if a science denialist refuses the existence of gravity using the same “logic” that they use to reject the existence of evolution.
NCSE does not deny gravity & it is mentioned at the beginning of the article that it is a satire. Flat-Earthers failed to notice that, and it became a hoax that they use to support their false belief. The author probably did not expect there are far more extreme denialists that can go as far as to reject gravity & even beyond.
Objects fall down because of gravity. Flat-Earthers deny gravity & wrongly claim they fall down because of density. We can disprove flat-Earthers’ claim by setting up two different weights of the same material (thus, the same density) against each other using a balance. We can see the objects’ densities are not why they fall down.
No correlation exists between salinity and tide. These bodies of water have higher salinity than the seawater average, yet they have no tides or smaller tides than the ocean.
Tides occur on the ocean with salt water, but seemingly not on lakes with fresh water. Flat-Earthers use it to “prove” salinity causes tides. In reality, there are bodies of water with a higher salinity than the ocean but smaller tides.
Earth’s gravity causes water’s surface to curve with the same radius as Earth’s. On glass with a diameter of 10 cm, Earth’s gravity causes the water to form a curvature of 0.00000002 cm, outside other factors like surface tension.
Flat-Earthers like to demand that we prove water curvature in a glass of water. In reality, whatever the container, the curvature of the water surface remains the same as Earth’s radius. On a glass of water, it will be too small to observe.
Earth’s gravity pulls things toward Earth. Satellites can stay up there because they are orbiting. They are moving at the right speed and right direction to counter the pull of gravity.
Flat-Earthers claim that satellites should fall down if gravity pulls toward Earth. In reality, we do not just launch satellites to space. We also give them the correct speed & direction, so they neither fall toward Earth nor keep going farther away.
The gravitational acceleration exerted by the mass of a wet, spinning tennis ball is too small compared to the centrifugal acceleration generated by its rotating motion. As a result, the water escapes away from the tennis ball, unlike Earth.
A wet spinning ball is a sphere, spinning & wet, like Earth. But the water goes away from the ball, unlike Earth. Flat Earthers use it to “disprove” spherical Earth. In reality, the magnitude of the involved accelerations in the two cases are different.
“Down” is the same direction as Earth’s gravitational acceleration, toward Earth’s center. “Up” is the opposite, or away from Earth’s center. This applies to all observers on Earth.
Flat-Earthers like to question & ridicule about what would occur on the people “down” there. They just do not understand that to the people on the other side of Earth, “down” is still toward Earth’s center, like it appears to everyone else.
Gravity is a natural phenomenon by which all things with mass or energy are brought toward one another. Today, gravity is explained by two theories: Newton’s law of universal gravitation and Einstein’s general relativity.
Flat-Earthers treat the existence of the two theories as a supposed conflict, and they use it as “evidence” of wrongdoing. In reality, these are two separate theories that explain the phenomenon of gravity. Einstein’s is more accurate yet more complex. In contrast, Newton’s is simpler but less accurate. Despite having been superseded, Newton’s gravity continues to be used as an excellent approximation of the effect of gravity in most applications.
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.