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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
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 optical illusion
Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide v ...
, 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 () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
. Hundreds of gravity hills are recognized worldwide.
The slope of gravity hills is an optical illusion, although sites are often accompanied by claims that magnetic
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
or supernatural
Supernatural refers to phenomena or entities that are beyond the laws of nature. The term is derived from Medieval Latin , from Latin (above, beyond, or outside of) + (nature) Though the corollary term "nature", has had multiple meanings si ...
forces are at work. The most important factor contributing to the illusion is a completely or mostly obstructed horizon
The horizon is the apparent line 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 line divides all viewing directions based on whether i ...
. Without a horizon, it becomes difficult for a person to judge the slope of a surface, as a reliable reference is missing. Objects which one would normally assume to be more or less perpendicular
In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...
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. As a conclusion, researchers from Universities of Padova and Pavia
Pavia (, , , ; la, Ticinum; Medieval Latin: ) is a town and comune of south-western Lombardy in northern Italy, south of Milan on the lower Ticino river near its confluence with the Po. It has a population of c. 73,086. The city was the capit ...
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
An Ames room is a distorted room that creates an optical illusion. Likely influenced by the writings of Hermann Helmholtz, it was invented by American scientist Adelbert Ames Jr. in 1946, and constructed in the following year.
Usage and effect ...
, 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 s ...
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 up ...
* The Crooked House
The Crooked House is a pub and restaurant in South Staffordshire, England.
Its name and distinctive appearance are the result of 19th-century mining subsidence. One side of the building is now approximately lower than the other.
It stands i ...
– a building with an internal gravity hill optical illusion.
References
External links
* {{Optical illusions