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.
Continue reading “Uniform Circular Motion”
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.
Continue reading “Hill Sphere”
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.
Continue reading “Elegance”
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.
Continue reading ““What is Gravity””
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.
Continue reading “Repulsive Force”
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.
Continue reading “Weightlessness, Free Fall, and Microgravity”
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.
Continue reading “Eötvös Effect: Direct Evidence Earth is a Rotating Sphere”
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.
Continue reading “Flat-Earthers’ Alternative Facts for Gravity”
An airplane relies on the lift from its wings, which depends on the airplane’s speed and the air density. As a result, a cruising airplane will fly at a constant altitude, following the curvature of the Earth.
Flat-Earthers claim if Earth is a sphere, an airplane has to dip its nose down periodically, or it would fly into space. In reality, an aircraft will follow Earth’s curvature and is unable to fly to space even if the pilot deliberately attempts to do that
Continue reading “Airplanes Will Never Fly Into Space”
Rocket launches have a curved trajectory because their objective is not only to reach space but also to enter Earth orbit. To achieve it, a spacecraft needs to gain a sufficient horizontal speed, parallel to Earth’s surface.
Flat-Earthers claim the curved appearance of a rocket launch trajectory “proves” rockets never reach space. In reality, it is caused by the motion of the rocket parallel to Earth’s surface, perspective effect, and the curvature of the Earth.
Continue reading “Curved Appearance of a Rocket Trajectory”
A fictitious force is a force that appears to act on every object when the frame of reference is accelerating. The term “fictitious” does not mean the force does not exist, but it is not an actual force that arises from an interaction between objects.
Flat-Earthers noticed gravity is considered a fictitious force and use the fact to “prove” gravity does not exist. In reality, we can feel a fictitious force. It is merely a term we use for forces that arise due to an accelerating frame of reference.
Continue reading “Fictitious Force”
The Cavendish experiment was the first experiment to measure the force of gravity between masses in the laboratory and the first to yield accurate values for the gravitational constant.
Flat-Earthers are in a constant effort to discredit the Cavendish experiment. They would invent various “explanations” to “explain” the result of the experiments. However, the experiment was not only done once by Henry Cavendish in 1797-1798, and has been replicated numerous times by multiple independent parties for centuries, all yielding consistent results.
Continue reading “Cavendish Experiment”
During cruising, an airplane is practically level. It is flying perpendicular to the direction of gravity. The aircraft is still flying following Earth’s curvature and continuously changes its orientation. However, not only its orientation changing but also the direction of gravity, having the same amount of change. As a result, a spirit level on a flight will not show us the difference in orientation of the airplane due to its motion following the curvature of the Earth.
Continue reading “Spirit Level on an Airplane”
The electromagnetic force is a type of physical interaction that occurs between electrically charged particles. Electromagnetism is different from gravity. Both phenomena are real but have different characteristics.
Flat-Earthers refuse to accept gravity, and some of them use electromagnetism in place of gravity to explain the various phenomena that are explained by gravity. In reality, electromagnetism has different characteristic from gravity, and cannot explain the various phenomena that are explained by gravity.
Continue reading “Electromagnetism”
An egg will generally sink in freshwater, but if we pour salt into the water and stir it, then the egg will start to float. The reason is that after salt is added, the density of water increases. However, the relationship between density and if the egg floats or sinks is not a direct causality.
Flat-Earthers claim that the phenomenon “proves” things fall because of density, and that gravity does not exist. In reality, the density of the water determines the magnitude of buoyancy the egg receives. If the buoyancy is higher than the weight of the egg, the egg will float, and vice versa.
Continue reading “Egg and Salt Water”
Shell theorem is a simplification stating that a spherical body affects external objects gravitationally as though all of its mass were concentrated at a point at its center.
The direction of Earth’s gravity toward the center of the Earth made some flat-Earthers to assume that we think gravity is caused by something in the center, and that our inability to go there “disproves” gravity. They are wrong. Earth’s gravity is the result of the entire mass of Earth. Using the center of the Earth is merely a simplification.
Continue reading “Shell Theorem”
Gravity is the attraction between objects with mass. The higher the mass, the greater is the gravitational attraction. Gravity is not the result of the shapes of the objects.
Flat-Earthers like to perform the ball-and-water ‘experiment.’ They spray water to a ball, then observe the water does not stick to the ball the same way the ocean water curves over the surface of the Earth. They would wrongly conclude that “gravity does not exist.” Gravity does not come from the spherical shape of objects, Continue reading “The Ball and Water ‘Experiment’”
The gravity of Earth varies on the different location on Earth. The variation is caused by the difference in latitude, altitude or depth, and local geology & topography. In most cases, the centrifugal acceleration from Earth’s rotation is also already accounted for in the value of Earth’s gravitational acceleration.
Flat-Earthers claim that according to science, the Earth’s gravitational acceleration is always constant at 9.8 m/s² everywhere on Earth. And they are using the claim to prove Earth is not a rotating sphere. In reality, the magnitude of Earth’s gravitational acceleration varies on the different location on Earth.
Continue reading “The Variation of Earth’s Gravitational Acceleration”
Albert Einstein used thought experiments as a tool for formulating his theories. His theories provided predictions that can be tested in observation and experiments. He did not perform the observation and experiments himself. Others did and confirmed his theories.
Some flat-Earthers dismiss Einstein’s theories —especially those about gravity— on the basis that they are founded on thought experiments and daydreaming. They are wrong. His theories have been repeatedly confirmed by various experiments and observation performed by many others, even to this day.
Continue reading “Einstein’s Thought Experiments and Daydreaming”
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 refer to as ‘weight’.
Many flat-Earthers fail to understand that the gravitational force is just another name for ‘weight’. Many misconceptions in the communities of flat Earth victims arise from such a misunderstanding.
Continue reading “Weight = Gravitational Force”