While some families are putting helmets and knee pads on their children in order to ride a bicycle, others are installing trampolines in the backyard. Here are some ways new space age materials can intensify the thrill we used to get from an old-fashioned rope swing. As a mother, I would not personally recommend any of the following activities, but boy, are they fun to watch!

Zip Line

Zip lines, sometimes referred to as flying foxes, consist of a pulley mounted on a cable suspended between two points. The rider holds on to the pulley (or in some cases, a harness is attached) and slides between the two points, usually by the force of gravity. In my backyard, we use a zip line to attach the dog's chain, giving her more room to roam (the dog is, of course, on the ground). In some remote areas of the world, people use zip lines for transportation or shipping. Others make money from tourists, such as the mile-and-a-half zip line in Sun City, South Africa, which resembles tethered hang gliding. Image by Flickr user Travis Jon Allison.

Some who've tried the professional zip line installations can't wait to recreate the idea at home for their continued use. You'll want to scale things down a bit for your backyard. Here's how to install your own zip line. You should be able to build an industrial-grade apparatus with brakes for about $300. You can even go online to design your zip lineto meet the specifications of your backyard (incline, trees, etc).

Water Blobbing

Water blobbing involves catapulting one swimmer into a lake or pond by another swimmer jumping onto a partially-inflated balloon. The activity came home from the military, after sailors found they could bounce into the water off flexible floating fuel tanks that were towed by ships. Blobbing became popular at summer camps. Image by Flickr user wka.

Here's the short course on how to blob. The equipment costs run from hundreds of dollarsto thousands of dollars. Liability insurance is not included.

Human Slingshot

The strong but flexible cord used in bungee jumping has spawned other thrills, such as the human sling shot thrill ride you see at various amusement parks. This videogives you an idea of how it works. But why limit such danger to professional amusement parks? The Pope family in Utah built an enormous human slingshot in their backyard.

It suddenly became a very good thing to be a friend or family member-if you wanted to experience a cheap but memorable thrill.

Word got around, and finally the Travel Channeldecided to look into this backyard slingshot.

See also: Homemade Roller Coasters and Extreme Sports Destinations.