Physics Demo Number: 095

Approximate Run Time: 5 min

Differential Pressure Bottle With Stay-Open Balloon

Demo Description

Inflate a balloon in a flask with a round , stopper -pluggable, hole in its bottom (with the stopper out).

Insert the stopper before removing your mouth from the balloon. The stopper-sealed flask will not allow the balloon to deflate.

Scientific Principles

  • Differential Pressure

1

Equipment

  • 1-liter round flask with balloon

Equipment Location

  • 1-liter round flask is in kit (095) on [D-2-6].

2

3

Instructions

Photo 1 shows a one liter round flask with a hole in its bottom and a rubber stopper to seal the hole when desired. The stopper may be removed and the balloon blown up as seen in the next photo.

The intriguing thing is that in photo 2, there is no plug in the neck of the balloon, as may be seen in the photo 3.

The point is that the stopper was put into the bottom hole after inflation of the balloon.

In essence, if the balloon tries to empty itself, the pressure in the sealed volume of air between the outer surface of the balloon and the inside wall of the flask will try to decrease and thus counteract the attempted change in balloon configuration.

One may fill the balloon (as configured in photos 2 and 3) with water and then remove the rubber plug while holding the neck of the flask vertically upwards and achieve a nice upwards spouting jet of water.

But this water jet could pose a threat of damage to the computer interfaces in our Lecture Halls and is not recommended.

 
Writeup created by David A. Burba
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