Level: Elementary to Middle.
Time involvement: 10-15 minutes.
At first thought this seems impossible. The normal way to inflate a balloon is to use some sort of blower or pump to force the air into the un-inflated balloon. Even our lungs can supply the needed pressure. This an example of “thinking outside the box” or “turning the problem on it’s head”. Amazingly, a quart jar and an automotive hand operated vacuum pump can solve the problem. The above photo is a group of related “air-pressure” toys. The quart jar with special lid and the hand operated vacuum pump are on the left
Discussion: We live at the bottom of an “ocean of air”. The pressure at sea level is 14.7 pounds per square inch. The solution is to reverse the normal situation of requiring additional pressure inside the balloon to inflate it. By using the 14.7 pounds of pressure always available (at sea level) we just have to remove some of the pressure on the outside of the balloon.
As can bee seen in the photograph, the quart jar has a specially constructed lid. There are two holes. The first hole has a tube inserted in it with the balloon attached on the inside. The second hole is another “port” which allows air to freely enter or exit as needed. In this case the hand pump will be connected through this hole and a partial vacuum will be created in the jar outside the balloon. Before attaching the hand pump the demonstrator first uses his/her mouth to inflate the balloon enough to prove that there are no “tricks”. After removing his/her mouth from the “inlet tube” the balloon will deflate by itself caused by its elasticity and some help from the atmospheric pressure allowed to enter through the second port.
A few words about the vacuum pump. This is not a toy. Sold in automotive stores, this tool is used by mechanics to troubleshoot problems and make adjustments to the vacuum system on cars. It is a simple hand operated piston pump with a gauge to keep track of the pressure or vacuum created. The vacuum pump has a short hose that allows the pressure/vacuum to be delivered to the desired location. For our demonstration the hose is connected to the second port. The opening to the balloon must not be blocked! With a few strokes of the pump the balloon will begin to inflate. It is not necessary to completely fill the jar with the inflated balloon for students to get the idea. At this point it’s fun to point out that the mouth of the balloon is completely open and a small insect could fly in and out of the balloon if it desired.
This is another “I’ll believe it when I see it” demonstration. Magicians do tricks which, through, illusions fool our beliefs. The balloon is actually inflated but in an unusual way that we might not expect. As discussed in the Triangle Rollers lesson common sense based on experiences would lead us to believe that the task is impossible. Here again, however, the solution involves manipulating the outside pressure by sealing the balloon in a jar and removing some of the surrounding air.
Learn more: Balloons and soap bubbles have always been fascinating to watch. From freezing a soap bubble with dry ice to the trick of sticking a pin in a balloon without breaking it. (Attach a piece of tape first then put the pin through the tape) the internet has many do-it yourself tricks.