The runs are about 500-800 metres and the sport was first introduced in Rotura, New Zealand. It is however now in vogue in many countries.
The ball is a double-sectioned sphere, with one ball inside the other with an air layer between. This acts as a shock absorber for the rider, dampening bumps while rolling. Many balls have straps to hold the rider in place, while others leave the rider free to walk the sphere around or be tossed about freely by the rolling motion - water can be added inside, and this is commonly called a "water ride". A typical ball is about 3 metres in diameter, with an inner sphere size of about 2 metres leaving a 50–60 centimetre (20–24 in) air cushion around the riders. The inner and outer sphere are connected by hundred of connectors and filled with air.
Caution: There have been couple of incidence of injury and even death of riders. So before embarking in this sport one must take into account all necessary safety precautions and check the safety features available at the Zorbing site.
Here are few images taken at Rotura, New Zealand.
Image from Flickr is by Planetgordon.com
Image from Panoramio is by jfthompson
Image from Panoramio is by Matt Heap
Image from Flickr is by Wilposh
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Source of Info: Wikipedia