Peppa Pig® knew it best when she said that there are two types of balloons in this world: ones that go up and ones that go down. The physics behind Peppa’s profound insight are that some balloons are filled with things like helium and some with air (or water, if you roll that way). The reason that the helium-filled balloons float up and out of your child’s possession is that the density of the balloon with its contents together is lower than that of the surrounding air. This principle also keeps large metal ships afloat. Although the metal of which the hull is made is denser than the seawater, the hull filled with air is lighter and floats. Meanwhile, the breath-filled balloon has a similar fate to a water-filled ship.
A child hugging a balloon is like what happened before the big bang.
Speaking of balloons going up and down, have you ever played a game of balloon tennis? It is perfect for playing indoors with your kids. The balloon is slow enough for them to have a chance of hitting it back at you but fast enough to keep things interesting. Just use a pair of regular tennis rackets, or your hands if you have nothing else available. The balloon must not touch the ground and we’ll see who drops it first. You can up the difficulty by adding a second balloon or by using a balloon with less air inside (it moves faster). Of course, you could dispense with tennis rackets altogether and just have a balloon mayhem wherein you all try to keep several balloons in the air by any means necessary.
If you want to really amaze your children (and yourself), grab a balloon and a hairdryer. Switch on the hairdryer and aim it diagonally upwards. Now carefully place a balloon in its exhaust stream and watch it just float in place. Unbelievable! As it turns out, the scientific term for magic might very well be ‘Bernoulli’s principle’. All hot air aside though, this trick still blows me away.