What you Need
All you need is a party balloon, and some enthusiasm
What to do
This is very simple, first try hitting the balloon gently and see how it travels
Now try bashing it really hard, does it do what you would expect?
What may happen
You should find that if you hit the balloon gently it flies across the room and slows down gently.
If you hit it really hard though it moves very fast for a bit then suddenly slows down or changes direction.
Why does it happen?
If you hit the balloon gently the air will flow around it, there will be quite a lot of friction compared to the mass of the balloon so it will slow down gently.
If you bash the balloon really hard you are not just making the balloon move fast you are also making the air around it move fast, and there is actually more energy in the rapidly moving air than in the balloon itself.
While it is going fast the balloon seems to drag (or be pushed along by) a chunk of air behind it (which the smoke allows you to see), this seems to be circulating slightly, a little bit like a smoke ring.
After a little while and as the balloon slows down a bit this arrangement gets unstable and the air behind the balloon becomes more unstable and pushes past the balloon, entirely changing its direction and sometimes pushing it backward.