How does gravity hill work

This YouTuber sent a ball down a road in Pennsylvania, only to have it roll back up the hill towards him:. Phenomenal Travel Videos. So what's actually going on here?

Turns out, these bizarre natural phenomena are just an elaborate optical illusion - an illusion so good, it'd be impossible to believe it without the proper equipment. But if you get some surveying equipment or GPS markers to actually measure the difference between the 'top' of the slope and the 'bottom', you'll realise that everything is actually in reverse. But if a hill is physically sloping one way - so much so that cars actually gain quite a bit of momentum when they start drifting 'up' - how could our eyes trick us so bad every time?

Whenever you travel to the many amazing destination throughout Pennsylvania, you'll find yourself traveling across the miles and miles of roadways that crisscross the state. However, what if the roadways were your destination?

At Pennsylvania's gravity hills, they are. What is a gravity hill? A gravity hill is a spot where cars, water, balls, etc. While they are quite amazing and really look and feel as if things are rolling up hill, they are optical illusions. However, that doesn't stop legends of ghosts or unexpected gravitational changes from being told.

How to work a gravity hill. So, how do you make your attempt to defy gravity at a gravity hill? First, check to make sure there is no one behind you. If clear, put your car in neutral and take your foot off of the break. Your car will slowly pick up speed as you appear to roll uphill.

Even though it's an optical illusion, you really will feel like you are defying gravity as your car rolls backwards. Safety when trying a gravity hill. It's worth noting that all three of the gravity hills listed here are on public roads.

If trying a gravity hill, use extreme caution as you will be traveling backwards and towards any oncoming traffic. Make sure to always look behind you as you roll and give the right of way to any cars that are simply passing on the road. Your car will seem to defy gravity, slowly rolling uphill. A glitch in spacetime could cause the laws of physics to unravel into backwards chaos. An army of angry ghosts could be muscling your car to the top of the hill with nothing but their bare ghost hands.

All of these sites have one thing in common other than their apparent disregard for gravity : the horizon is either curved or obstructed from view. This is key. Horizons provide us with a very useful reference point when we're trying to judge the slope of a surface. A study published in Psychological Science in found that false horizon lines can be deceiving to observers perceiving landscapes. A ball rolling on a gravity hill appears to stop and roll back up the hill.

Phenomenal Travel Videos. Without a true horizon in sight, objects such as trees and walls — which your eyes use as visual clues to determine perpendicularilty — can play tricks on you.