When you blow up a balloon with your breath, you’re filling it with a mixture of nitrogen, oxygen, and a little bit of carbon dioxide. And when you let go of it, it falls down to the floor. Why does it do this? And how could we prevent it from doing so?
Think of it like rocks in water. If you throw a stone into a river, it will sink to the bottom. This is because the rock is more dense than the water around it, due to its higher mass that’s concentrated in a smaller volume. The water tries to push back against the rock with a buoyant force, but the force of gravity is stronger, so the rock sinks. In our example, the balloon filled with nitrogen, oxygen, and carbon dioxide is the rock, and the atmosphere around us (made up of nitrogen and oxygen) is the water. Even though the gases inside and outside the balloon are approximately the same, the balloon material adds to the weight, causing it to sink down. If we wanted to get the balloon to float, we would have to either decrease its density or increase the density of the air around it. By putting a low-density gas like helium or hydrogen inside the balloon, we can make it light enough to float.
But the cooler thing to do is to change the density of the air around the balloon! We can do that here at AstroCamp by allowing dry ice to heat up and change into its gaseous form: carbon dioxide. The higher density of carbon dioxide makes it so that the buoyant force is way stronger on the balloon, which causes it to float!
Density experiments are really cool. You can actually learn a lot about them if you try it at home! Try mixing cooking oil and water with each other, then put object like rocks or pieces of wood inside! See what happens and let us know in the comments below!
Written By: Scott Yarbrough