Gravity hill

"Magnetic hill" and "Mystery hill" redirect here. For other uses, seeMagnetic Hill (disambiguation)andMystery Hill (disambiguation).

Water appearing to run uphill atMagnetic HillinNew Brunswick

Magnetic Hill inMoncton,Canada

Agravity hill,also known as amagnetic hill,mystery hill,mystery spot,gravity road,oranti-gravity hill,is a place where the layout of the surrounding land produces anoptical illusion,making a slight downhill slope appear to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill againstgravity.

The slope of gravity hills is an optical illusion,although sites are often accompanied by claims thatmagneticorsupernaturalforces are at work. The most important factor contributing to the illusion is a completely or mostly obstructedhorizon.Without a horizon, it becomes difficult for a person to judge the slope of a surface, as a reliable reference point is missing. Objects which one would normally assume to be more or lessperpendicularto 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 ofPadovaandPaviain 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 theAmes room,in which objects can also appear to roll against gravity.

The opposite phenomenon—an uphill road that appears flat—is known inbicycle racingas a "false flat".

See also

• List of gravity hills
• The Crooked House– a building with an internal gravity hill optical illusion.

External links

• Dunning, Brian(January 11, 2011)."Skeptoid #240: Mystery Spots".Skeptoid.