Science Buddies: "Ask an Expert"

Hi, I was wondering how to put an exact amount of air (in cubic centimeters) in a balloon. I understand the water displacement technique for FINDING the volume of a balloon but I need a way to PUT a certain amount of air in a balloon.

Thank you!

heyrochons - The benefit of using the water displacement approach is that it is relatively easy to physically measure the volume of the air in the balloon. The problem is that in immersing the balloon in the water, the pressure on the balloon is increased and therefore a smaller volume than if the balloon is in an atmospheric environment. The air in the balloon is also under pressure, so the true volume of the air, at standard atmospheric pressure, would also increase. If you had an accurately measured volume of air, say 1000 cc at standard atmospheric pressure, and inserted it in an elastic balloon, the volume of the balloon might be only 950 cc because of the higher pressure inside the balloon. If you then inserted that balloon in a water tank to measure the displacement, the volume might only be 900 cc (depending how far below the surface of the water the balloon was placed). I think it's important to remember these things and understand what it is you truly want to measure and why, for your particular experiment. You might want to refer to Boyle's law for more information.

Rick Marz