Gravity hill
From Wikipedia, the free encyclopedia
A gravity hill, also known as a magnetic hill (and sometimes a mystery hill or a gravity road), is a place where the layout of the surrounding land produces the optical illusion that a very slight downhill slope appears to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill. There are hundreds of known gravity hill locations around the world.
[edit] Explanation
The slope of a gravity hills is an optical illusion, although tourist guides may claim natural or even supernatural forces are at work. The most important factor contributing to the illusion is a completely or mostly obstructed horizon; without a horizon, judging the slope of a surface is difficult as a reliable reference is missing. Objects one would normally assume to be more-or-less perpendicular to the ground (such as trees) may actually be leaning, offsetting the visual reference.
These "paranormal" sites also tend to have names like "Haunted Hill", "Magnetic Hill", or "Anti-gravity Hill", reflecting attribution of the properties of the area to such "mysteries" as the supernatural or magnetism. While humans also have a sense of balance to determine the inclination of the ground, visual cues can override this sense, especially if the inclination is shallow.
[edit] See also
- List of magnetic hills, a list of geographical gravity hill and their locations.
- The Schiehallion experiment, a 1774 experiment that estimated the mass of the earth using the deflection caused by the mass of a mountain.
[edit] External links
- Magnetic Hill International International Directory of Magnetic Hills, Gravity Hills, Mystery Hills, and Magnetic Mountains
- Mystery Spots and Gravity Hills at About.com
- The Enigma Project
- Scientific explanation of the phenomenon
- Sloping off: Can cars roll uphill? at NewScientist.com
