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Hills That 'Defy' Gravity

Thursday, February 08, 2007

A "gravity hill" is a place where one of the four forces of nature goes haywire. Up becomes down, and down becomes up. Or does it?

To be more specific, a gravity hill is a place where you can put your vehicle in neutral, and sit back as it rolls "uphill." In the Delaware Valley, there are two such "gravity hills." One is in Mercer County, New Jersey. The other is in Bucks County, Pennsylvania.

We visited both. We simulated what each "hill" supposedly does to a coasting car. And we spoke to nearby residents about the legends that surround these mysterious places.

HOPEWELL TOWNSHIP, NEW JERSEY - January 18, 2007

The first one is in Hopewell Township, New Jersey - which is just north of Trenton. The road is Pennington-Harbourton Road which then turns into Pleasant Valley Road.

Myself and photographer Bill Long met Bob Miller there. He is the zoning officer for the township, and has known about this unusual stretch of roadway for decades.

The story of Hopewell Township's gravity hill goes like this: many decades ago, there were two farmers in Hopewell Township who found themselves in some great dispute - perhaps over property. One day, in their anger, they smashed plows into each other. The metallic collision produced a great deal of sparks - and a bizarre reversal of the Earth's geomagnetic field.

Again, according to the legend, it is in this very spot that humans can experience a variation of the Earth's gravitational field, allowing objects (like cars) to be "pulled" up a hill. The stretch of roadway is about 100 yards.

Well, Action News had to try this. I got into our rental minivan, pulled up to the very spot that Miller told me was the starting point, and looked ahead. Yes, it indeed looked like I was sitting on the bottom of a slight incline. I threw the transmission into neutral, took my foot off the brake - and it happened.

Sure enough, the minivan started rolling; it picked up speed right away, going to about five m.p.h. It slowed down a bit, and then began rolling a little faster again. How is this happening?

BUCKINGHAM TOWNSHIP, PENNSYLVANIA - February 1, 2007

We also visited a gravity hill on Holicong Road in Buckingham Township, Bucks County. This one was, like the first, along a country road in a rural area. We were unsure of its exact location, so we asked some of the local residents. A couple of nice fellas took us to the place we were looking for.

Once again, we tested this gravity hill for ourselves - more than 10 times in a row. Vehicle in neutral, foot off the brake, we start to roll. And once again, it seemed as if we were rolling uphill. What made this location a bit different from the Hopewell Township gravity hill, was that it looked like we were going uphill - from both the front and back vantage points. The optical illusion would fool someone watching our vehicle roll, whether he or she was standing at the beginning of the stretch of roadway, or at the end.

The Buckingham Township legend seems to be connected to a nearby house of worship: the Mount Gilead African Methodist Episcopal Church, which is about a half mile away from the gravity hill. One resident tells stories of people running laps around a cemetery next to the church, in a race with the devil. If one wins the race, one gets to live. If one loses...well, let's just say you wouldn't want to come in second place for this competition.

How exactly the story fits in with the illusion of your car or truck coasting "up" a hill further down the road, is unclear.

PUTTING THE "HILL" TO THE TEST

We came prepared when we visited both locations. We had a carpenter's level.

We took three readings at the Hopewell Township gravity hill. When we set it at the starting point, the level's bubble was clearly floating on the left side (when I say left side, I mean on the side where the gravity hill begins - the right side would be the end). This explains why the minivan begins to roll at a rapid pace immediately: it's because this is not an incline, but a slight decline. You can review pictures of these readings, and many other photos from the story, by going to our gravity hill slideshow.

The second reading was taken in the middle of the gravity hill. Here, the level's bubble still floated on the left side, but not as much. This explains why the minivan slowed down slightly when it reached this point - the hill's grade is reduced here.

Our third reading was taken at the end. And once again, the level's bubble floated to the left side, a tiny bit more than the second reading, but not as much as the first.

Our conclusion: this 100-yard stretch is not an incline at all. The minivan rolls because it is going slightly downhill.

We spotted further evidence to support this conclusion: there is a small drainage ditch on the right side of the gravity hill, and the water is running in the direction that the minivan was "coasting."

We took similar readings at the Buckingham Township location. And sure enough, each reading we took indicated the gravity hill leads downhill, not up. We also had a compass with us this time to look for evidence of strange magnetic fields, which are sometimes part of a gravity hill story. Nope. The compass pointed north, just as it should have.

OPTICAL ILLUSION

We spoke to David Goldberg, an assistant professor at Drexel University who teaches astrophysics. It was a pleasure to meet him, because in addition to knowing why things go up and down, he is also a great mind when it comes to cosmology (a fascinating subject near and dear to my heart). But for this story, our focus would have to be physics.

Dr. Goldberg says gravity is not constant on Earth. That is probably not surprising to you; it is why astronauts float around in weightlessness while on the International Space Station, high above the planet. However, when it comes to measuring the difference of gravity between, say, Mount Everest (the highest point on Earth) and Death Valley, California (the lowest point on Earth), it is barely detected - let alone be felt by a human being.

So any claims that a particular point on Earth possesses unusual gravitational forces, according to Dr. Goldberg, is preposterous. It is just not good science. Same thing goes with claims of bizarre electromagnetic forces pulling metallic vehicles up a hill. Dr. Goldberg says if that were happening, cars wouldn't be the only things feeling the magnetic "pull." You'd see other, much lighter, metallic objects (like our compass) being attracted toward the end point of the gravity hill.

So how does this thing work? It is simply an optical illusion. Dr. Goldberg says we orient ourselves with the Earth by using a number of stimuli: the pull of gravity, the fluid in our inner ear (called the endolymph), and the sights, sounds, and even smells around us. The vast majority of the time, this collection of stimuli helps us get it right. We can figure out when we are leaning forward, or backward, or going faster, or slower, or hanging upside down, or rightside up.

But every now and then, our ability to tell what is up and down goes a bit haywire. There may be some aspects of the topography that cause us to see things that aren't really happening. Let's say, as in the case of our gravity hills, the road disappears and there are tall trees in the distance, helping to frame the background. Perhaps our brains concentrate on this particular stimuli, ignoring other pieces of evidence (like water in a stream flowing ahead).

The illusion takes place. "I feel like I'm going uphill."

Yes, you feel.

But you are not.

(Copyright ©2014 WPVI-TV/DT. All Rights Reserved.)

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