Line of Sight: Determining if an Object is Straight or Flat

Light travels in a practically straight line over a short distance. We often use this property of light to determine if an object is flat or straight from visual observation.

Some flat-Earthers start with the wrong assumption that a specific object is flat, then attempt to redefine how our vision works from that. They are wrong. From visual observation, we can determine if an object is flat, not the other way around.

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‘Flat’ vs ‘Level’

‘Flat’ and ‘Level can mean approximately the same thing in everyday conversation. But in the context of science and engineering, they have different meanings. ‘Flat’ describes a planar surface. ‘Level’ means at the same height or perpendicular to the direction of Earth’s gravity.

Flat-Earthers interpret the word ‘level’ as if it always has the same meaning as ‘flat.’ However, in the scientific context, the two words have different meanings. Insisting that both words to have the same meaning is the fallacy of appeal to definition.

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Geoid and Altitude Above Sea Level

The geoid is the shape that the ocean would take under the influence of the gravity and rotation of Earth alone. The geoid is smooth but irregular because Earth’s density and surface are uneven. ‘Height above sea level’ is measured relative to the geoid.

Some flat-Earthers claim that measuring height above sea level is not possible if the Earth is spherical. They are wrong. Height/altitude/elevation is usually measured relative to the geoid, which is approximately a sphere. The geoid is a more accurate model depicting the shape of the Earth, compared to the spherical & ellipsoid model.

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Vacuum in Space and Earth’s Atmospheric Retention

The Earth retains an atmosphere because gravity pulls air particles toward the center of the Earth. Without something affecting the air —like gravity— air particles would move toward lower pressure, and Earth would lose its atmosphere.

Flat-Earthers claim that Earth should not be able to have an atmosphere because without any barrier separating Earth’s atmosphere and space, it would have been sucked by the vacuum in space. They are wrong. Gravity pulls air and allows Earth to retain an atmosphere.

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The Ball and Water ‘Experiment’

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’”

Human Perception of Speed and Acceleration

When aboard an airplane flying at cruising speed, we will not be able to feel that the plane is, in fact, moving at speed of more than 900 km/h. But if the plane changes its speed, turns or changes its altitude, we can easily feel it.

The same thing happens with the motion of the Earth. Due to Earth’s rotation, the surface of the Earth is moving at 1656 km/h near the equator. We never feel it because the speed is constant, or in other words, the acceleration is zero.

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Airplane and Earth’s Rotation

An airplane exists on Earth. It has the same motion as the surface of the Earth, including the Earth’s rotating motion. The motion of the airplane itself is measured relative to the surface of the Earth.

Flat-Earthers think that due to Earth’s rotation, an airplane should not be able to fly east or land. They are wrong. The speed of an airplane is relative to the surface. It retains the motion of the Earth and does not need to chase Earth’s rotation.

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Einstein’s Thought Experiments and Daydreaming

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.

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Magnetic Poles

Every magnet has a north pole and a south pole. The opposite poles of the different magnets attract each other, while the same poles of the different magnets repel each other. It is not possible to have a magnet with a single pole.

Flat-Earthers proclaim that Earth cannot be a sphere because if a compass really points to the north pole, then on the equator, it should point 45° downward. They are wrong. A magnet does not only have the north pole, but it also has the south pole which is attracted to the north pole of Earth’s magnetic field. Near the equator, both forces are balanced and pull the compass’ needle to both Earth’s poles at the same time. A perfectly balanced compass will be level near the equator.

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Lunar Phase: Earth’s Shadow has Nothing to do with It

It can be surprising that many people believe that the lunar phase is caused by the Earth casting its shadow on the surface of the Moon. Flat-Earthers are no exception. But they take it one step further and use the misconception do “disprove” the fact that Earth is a sphere. They are wrong. The lunar phase is the shape of the sunlit part of the Moon seen from the observer.

On the other hand, the phenomenon where the Earth casting its shadow on the surface of the Moon is called the lunar eclipse. Moon phase occurs all the time and undergoes a monthly cycle, while a lunar eclipse happens only a couple times in a year.

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Cavendish Experiment

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.

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Rayleigh Scattering

Earth’s atmosphere glows in blue because of Rayleigh scattering. It scatters sunlight to every direction. Bluish colors are scattered more than reddish colors. This results in the bright blue color of the sky in the daytime.

There are many misconceptions in the flat Earth community that arise from the lack of understanding of Rayleigh scattering.

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Weight = Gravitational Force

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.

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Horizontal Motion of Smoke

Smoke rises due to convection current. The solid particles emitted from a combustion process are carried by the hot air that rises because of its lower density than the surrounding air. The horizontal motion of smoke itself is affected by the movement of air surrounding it.

Flat-Earthers claim that a rising smoke without horizontal motion “proves” a stationary Earth. They are wrong. The horizontal motion of smoke is an effect of the horizontal motion of air relative to the smoke, and the motion of the object emitting the smoke is inconsequential.

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Frame of Reference

A frame of reference consists of an abstract coordinate system and the set of physical reference points that uniquely fix the coordinate system and standardize measurements. Speed or velocity is relative to a frame of reference. It is possible that two speeds/velocities are measured relative to a different frame of reference and thus cannot be directly compared.

Flat-Earthers would often compare two different speed measurements like an airplane moving at 900 km/h (560 mph) and Earth’s surface near the equator at 1674 km/h (1040 mph). They would conclude the airplane should not be able to catch up with Earth’s surface and would not be able to land if the Earth is rotating. They are wrong. The speeds are measured relative to the different frame of reference, and therefore, cannot be compared directly.

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The Dark Sky on the Lunar Daytime

On Earth, daylight sky is glowing in bright blue due to Rayleigh scattering. Sunlight is scattered in every direction by the oxygen and nitrogen molecules in Earth’s atmosphere.

Such the phenomenon does not happen on the Moon, causing the dark sky of the Moon. Flat-Earthers claim that the dark sky of the Moon captured by photos and videos taken from the Moon are “proof” there is misconduct. They are wrong. Just because Earth’s sky is bright blue, it does not mean it will be like that on the Moon and other planets.

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Determining the Visibility of a Star From Its Declination and the Observer’s Latitude

We can determine if a star is visible from a specific location using the declination of the star and the latitude of the observer, subject to other conditions like observer’s topology, the magnitude of the star, weather conditions, etc. It is possible to do this because Earth is a rotating sphere.

If the Earth is flat, every star would have been visible all night from every location. We don’t see the same stars every night because some of them are below the horizon and obscured by the Earth.

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Earth’s Atmosphere Rotation

Earth’s atmosphere is part of the Earth. It practically follows Earth’s rotating motion like the rest of the Earth. Due to various factors, Earth’s atmosphere has relatively small and uneven movement relative to the surface. We call it ‘wind.’ The fastest wind ever recorded is about 408 km/h, relative to Earth’s surface.

Many misconceptions about Earth arise from the wrong idea that only Earth’s solid body is rotating, but the atmosphere is not. If it is true, then we should always feel the wind with the speed of 1674 km/h near the equator, or more than 4× the fastest wind ever recorded. We don’t feel such a wind, and thus we know our atmosphere is moving at practically at the same speed as Earth’s surface.

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Theories of Gravity

Gravity is a natural phenomenon by which all things with mass or energy are brought toward one another. Today, the phenomenon of gravity is explained by two theories: Newton’s law of universal gravitation and Einstein’s general relativity.

Flat-Earthers take the existence of the two explanations as inconsistency in science and use it as a “proof” of deliberate misconduct. Such allegation is obviously only a result of their prejudice. The two theories are the correct explanations of gravity, and can reliably predict the outcome of the phenomenon.

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Buoyancy

Buoyancy is an upward force exerted by a fluid (liquid or gas) that opposes the weight of an immersed object. Buoyancy happens because the fluid has a pressure gradient. Pressure gradient occurs because the fluid is affected by acceleration, such as the Earth’s gravitational acceleration.

Flat-Earthers makes buoyancy as an “explanations” on how things fall. They are wrong. Without Earth’s gravitational acceleration, buoyancy will not occur.

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