Remember the balloons my son got for his birthday? Well two of them met with a tragic end.
He received three balloons altogether, one on it's own with an anchor on the bottom of the string and two others tied together with one anchor on both strings.
The next day he decided he wanted to see how they would float outside, so he took the pair that were tied together out to the front yard and was letting the wind carry them down the slope of the lawn. Then the unexpected happened, a gust of wind blew and picked up the two balloons and carried them away over the roof tops, with the anchor still attached. I guess the two together were buoyant enough with the gust of wind, that the anchor couldn't hold them.
My son was devastated and shocked. The tears lasted hours. The next day even after warnings from me, he insisted on taking the single balloon outside to test a theory. He said that only one balloon with an anchor, would not float enough for the wind to carry it away. Also he said there was less wind today.
So out he went to experiment with wind. On this day he was right, the wind did not carry the single balloon away. The above drawing is his documentation of the events. Results: weights on the bottom of two balloons need to be heavier than on one balloon, if you don't want the wind to carry them away. This concludes the great balloon experiment of 2009.