A gravity hill, also known as a magnetic hill, mystery hill, mystery spot, gravity road, or anti-gravity hill, is a place where the layout of the surrounding land produces an
illusion
An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people.
Illusions may ...
, making a slight downhill slope appear to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill against
gravity
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
.
Although the slope of gravity hills is an illusion, sites are often accompanied by claims that
magnetic
Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, m ...
or
supernatural
Supernatural phenomena or entities are those beyond the Scientific law, laws of nature. The term is derived from Medieval Latin , from Latin 'above, beyond, outside of' + 'nature'. Although the corollary term "nature" has had multiple meanin ...
forces are at work. The most important factor contributing to the illusion is a completely or mostly obstructed
horizon
The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...
. Without a horizon, it becomes difficult for a person to judge the slope of a surface, as a reliable reference point is missing, and misleading visual cues can adversely affect the
sense of balance
The sense of balance or equilibrioception is the perception of balance (ability), balance and Orientation (geometry), spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception ...
. Objects which one would normally assume to be more or less
perpendicular
In geometry, two geometric objects are perpendicular if they intersect at right angles, i.e. at an angle of 90 degrees or π/2 radians. The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', � ...
to the ground, such as trees, may be leaning, offsetting the visual reference.
A 2003 study looked into how the absence of a horizon can skew the perspective on gravity hills, by recreating a number of antigravity places in the lab to see how volunteers would react. In conclusion, researchers from the Universities of
Padua
Padua ( ) is a city and ''comune'' (municipality) in Veneto, northern Italy, and the capital of the province of Padua. The city lies on the banks of the river Bacchiglione, west of Venice and southeast of Vicenza, and has a population of 20 ...
and
Pavia
Pavia ( , ; ; ; ; ) is a town and comune of south-western Lombardy, in Northern Italy, south of Milan on the lower Ticino (river), Ticino near its confluence with the Po (river), Po. It has a population of c. 73,086.
The city was a major polit ...
in Italy found that without a true horizon in sight, the human brain could be tricked by common landmarks such as trees and signs.
The illusion is similar to the
Ames room, in which objects can also appear to roll against gravity.
The opposite phenomenon—an uphill road that appears flat—is known in
bicycle racing
Cycle sport is competitive physical activity using bicycles. There are several categories of bicycle racing including road bicycle racing, cyclo-cross, mountain bike racing, track cycling, BMX, and cycle speedway. Non-racing cycling spo ...
as a "
false flat".
See also
*
List of gravity hills
This is a list of gravity hills and magnetic hills around the world.
A gravity hill is a place where a slight downhill slope appears to be an uphill slope due to the layout of the surrounding land, creating the optical illusion that water flows u ...
*
The Crooked House
The Crooked House was a pub in South Staffordshire, England. Its name and distinctive appearance were the result of 19th-century mining subsidence which caused one side of the building to be approximately lower than the other. It was known as ...
– a pub (now demolished) with an internal gravity hill illusion.
References
External links
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{{Optical illusions