[thedoc (OP)]

When I was on holiday in Barbados there was a road that seemed to defy the laws of gravity. If you placed a football at the end of the road which was quite steep downhill, the ball moved up the hill. I thought it was some kind of optical illusion at first but tried it myself and the ball did indeed move uphill against gravity! how is this possible?
Asked by Brenda


                                       

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[thedoc (OP)]

We put this question to Amos Storkey, a lecturer in the School of Informatics in the University of Edinburgh...
Amos -   From the description, I would have guessed that this happened on Morgan Lewis Hill which is in the St. Andrews District, Barbados.  In fact, there are quite a few places like this in the world.  There are often known by names like magnetic hill or gravity hill, and they are basically places where your eyes deceive you into believing a downhill slope is in fact a slope uphill.
[img float=right]/forum/copies/RTEmagicC_800px-Orroroo_Magnetic_Hill.JPG.jpg[/img]So what makes us think that down is up?
Well first of all, we expect things like trees, lamp posts, buildings, cliffs, and so on to go straight up.  If something is almost vertical, the brain may prefer to believe that it is vertical if it can explain the difference by some other means.  The thing is that light, wind, and subsidence can affect tree growth and cause trees to slope.  Ground movement can also affect things like lamp posts, or telegraph poles often in a consistent way.  The overall landscape also makes a huge difference.  Sloped or obscured horizons and widening roads can give a perspective effect that a road that curves around is actually headed up.  A slight downward slope that goes over an edge can easily be interpreted as a summit. 
Finally, once the natural environment starts to look like a gravity hill, people come along and deliberately add things like wonky signs to enhance the illusion, and bring in tourists.  Well, wouldn’t you?  The brain sees all this.  If there was one sloping a tree, the brain will just put it down to a sloping tree.  But if there are a number of sloping trees and nonvertical cliff, and it looks like the road is headed up due to a sloping horizon, that’s it.  Your brain just says “it’s too much of a coincidence” and interprets it as the road going up instead.  And because this is all unconscious processing, there is nothing much you can do about it.

[Geezer]

You don't need to go Barbados. There is an "Electric Brae" (Croy Brae) on the A719 near Dunure in Ayrshire.

My dad used to turn off the engine in the car, put it in neutral, and we'd roll uphill!

[chris]

That's "up hill" in inverted commas, I presume?!

Chris

[Geezer]

That's "up hill" in inverted commas, I presume?!

Chris

Well, at the time, it did seem like uphill. Mind you, this particular observer was only about six years old  []

[Eric A. Taylor]

This sounds like a "Mystery Spot" to me. These are fairly common in the US, there is one in California, in the city of Santa Cruz. (http://www.mysteryspot.com/)

There is nothing very mysterious about it if you know how the trick is done. What you do is you build a house on a hill but build it as if it were on flat ground. Normally houses built on hills are built so the floor is flat. You have a natural expectation that this is ALWAYS done, but in a "mystery spot" the house is built so everything is parallel to the ground. The house is usually surrounded by a high fence so you can't readily see the house is all tipped. From inside it looks perfectly normal, but you notice gravity doesn't seem to pull straight down, rather it seems to pull at an angle.

In reality the ball is rolling down hill. All the other visual indicators are telling you it's rolling UP hill but this is just like a slight-of-hand magic trick like David Copperfield would do. (Did I just date myself?)

You get the same effect on a ship at sea. If you're bellow deck all the visual indicators tell you that you are in a room that is not moving, but your balance center in your ears tell you you are pitching too and fro. (It feels a little like being drunk) It's this conflict that causes some people to become sea sick. It's also why it's sometimes helpful to get to where you can see the horizon. If you see the horizon your eyes can tell your brain you are indeed pitching to and fro.

[Eric A. Taylor]

Just looked at the video on the site. Obvious advertising but it does show a ball rolling "up" hill. If you look at the video closely you'll see the answer to the mystery...HILLS.

[Geezer]

Eric,

If you give any more away, we'll have to kick you out of the Magic Circle.

http://www.themagiccircle.co.uk/

[tommya300]

http://www.sciencedaily.com/videos/2006/0609-the_mysterious_gravity_hill.htm

[imatfaal]

http://www.sciencedaily.com/videos/2006/0609-the_mysterious_gravity_hill.htm

  Thanks for that video Tommy.  Although my first thought was "that guy from mythbusters has really let himself go!"

[chris]

http://www.sciencedaily.com/videos/2006/0609-the_mysterious_gravity_hill.htm

  Thanks for that video Tommy.  Although my first thought was "that guy from mythbusters has really let himself go!"


That's hilarious - i thought the same thing when I first saw the video...!

[Eric A. Taylor]

I applied for a job once at M-1 (the shop that does Myth Busters. The guy does look a little like Adam Savage, however Adam clearly doesn't have that horrible east coast accent. Also if your from the NE US and your offended by that statement....in the words of Don Henley: Get over it. Everybody knows the west coast it the best  []

[Eric A. Taylor]

Eric,

If you give any more away, we'll have to kick you out of the Magic Circle.

http://www.themagiccircle.co.uk/

Maybe I don't want to BE in your stupid magic circle. I'm taking my ball and going home.  []

The David Copperfield reference reminded me of a HORRIBLE joke that was going around back in the day. The joke was that David Copperfield had AIDS. He'd gotten it by doing magic. ("Magic" Johnson was a basketball player who had contracted AIDS in the 80's, probably from a groupie. Personally I think he was very brave at the time. He needed to let the people he'd slept with know so they could be tested. The only way he could do this was by going public. I met him several years ago. He's still alive and something of a test case. I think his is the oldest case of AIDS who is still alive. He seems to carry it but is immune to the disease. Maybe it's the magic?)

[Dom]

I find it hard to beleive that explanation there scientitist guy! How could so many people, especialy those of us who can't be hypnotized, and easily solve almost all optical illusions, be so easily overcome by such things? I've seen hills like this before. With my own eyes, and I tell you when you go to the top while someone is on the bottom, and then do the same thing in reverse, you know what's up and down. So do you have any other suggestions?