Algodoo

The blob has no weight, simple.

It looks to me like it has very little weight 0.000010kg. So why would it go up or down.

Hi john, in phun air weighs 0.010 exactly, air friction is a button to turn "phun" into a vacuum or as it is on earth. With no air, a balloon will fall to the earth (assuming their is gravity). With air it will float, since it is lighter than air. I believe gravity if self explanatory lol!!. Since what you have is lighter than air, it will float, BUT ONLY WITH AIR. I hope i explained it well!

I'll try to put Jac's words in an even simpler context.. Basically Air is behaving much the same like water, just a lot less dense.. So while objects ahve to be much lighter than required for them to swim on water, they basically can "swim" on air, too.. watch hot air or helium baloons for one.. they are "swimming" in the air

Even simpler version. When you set things to really light, they float. Thats cause their less dense then air, and when your less desne, you float. Like humans and animals in water.

even simpler version. it floats..