Tuesday, June 12, 2007

PHYSICS ONLINE VERSION 101 ---- What happens to helium balloons when they float into the sky?

Cracker question because helium balloons are actually a pretty controversial topic. Some people argue that they are harmful to the environment because on returning to Earth, animals mistake them for food, eat them, and die. Now for this to happen, the balloons would have to come back down in fairly large chunks. These chunks would then have to either block the animal's airways and choke them, or become lodged in their digestive system causing a fatal illness. Neither of these outcomes sounds very nice for animals so it's worth investigating more.First of all, we'd better look at how balloons are released.

When helium filled balloons are handed out at public events, they usually come with a piece of string or ribbon attached. The attachment is either tied into the knot, or secured with a plastic disk. Either way, if these balloons are accidentally (or purposely) released, the attachment becomes litter and that's bad. I've only spotted a few balloons in the amazing amount of litter I see surfing here in Sydney, but they all had ribbons attached. So rule number one, don't let go of your balloons!In organised 'mass balloon releases' however, the standard practice is to tie a knot without any attachments. That means no bits of ribbon or plastic disks end up in the environment and the balloon industry argues that balloons themselves are harmless for two reasons.

First of all, only one hundred percent biodegradable latex balloons are used in mass releases. Research showed that these balloons degrade about as quickly as an oak leaf under similar conditions. But opponents argue that a balloon floating in the ocean would take a lot longer to degrade than it would on land. While it's hard to know whether balloons that have turned up in the stomachs of dead marine animals caused their death, the presence of a ribbon would be a very useful piece of information.The other argument is that helium balloons are claimed to reach a height of anywhere up to ten kilometres before shattering into tiny little pieces.

These pieces, it is said, would be too small to pose a threat to animals. Now the shattering effect sounds reasonable for two reasons. One is that atmospheric pressure is dramatically reduced at high altitudes, so a helium balloon expands as it rises and eventually explodes. If you inflate a balloon beyond its limits at room temperature, it will break into small pieces up to about ten centimetres long. But the elasticity of rubber decreases at very low temperatures so it is possible that helium balloons shatter into much smaller pieces as is often claimed.

Unfortunately, no one has followed a balloon up to see what really happens up there as far as I know. And on top of that, you have to keep adding air without tying a knot to over-inflate a balloon down here at sea level. It's hard to say whether the knot stays intact when a helium balloon explodes way up there.So there you go … simple question, long answer! If you're keen to find out more, do a quick internet search on the subject and you'll find heaps of info from both sides of the argument.

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