Pascal's bottle Buster . . . Not

Presenter: Tony Wayne, Albemarle HS, twayne@albemarle.org  

Va. SOL:

These can be found at http://www.pen.k12.va.us/VDOE/Superintendent/Sols/home.shtml

National Standards:

Copy and paste the correlating sections from http://www.nap.edu/readingroom/books/nses/html/6e.html#ps

Topic/Concept

Fluids: Vapor pressure/cavatation

Materials

·      Bottle with all labels removed

·      Rubber hammer

·      Plastic food wrap (Saran Wrap) about 6 in x 6 in.

·      Heavy leather glove …for safety

·      Water

·      Trash can with a liner

·      Goggles or face mask.

Safety Considerations

            Glass will be broken. Make sure you wear goggles and the glove on the hand holding the bottle. Have student s a safe distance away. Perhaps behind some kind of “blast shield.” Hold the bottle over the trash can or bucket to catch the broken glass and water.

Do not hit the top of the bottle with your bare hand. It's manly, yes, but stupid too because you are not modeling safe science techniques.

Presentation

Fill the bottle to the top with water. Cover the top of the bottle with the plastic food wrap. (I have found that with practice you do not need the plastic wrap. Make sure you are holding the top of the bottle level.) Hold it tight with your left hand. (Make sure your left hand is wearing a glove). Hold the bottle over a trash can. Firmly hit the top of the bottle with a rubber mallet in your right hand. (If you use a regular, metal-head, hammer the top of the bottle will shatter and cause injury you’re your left hand). When the top of the bottle is hit, the bottom will drop off in to the trashcan. The water in the bottle will also drop into the can.

How the physics is demonstrated

  This is often incorrectly described as an example of Pascal's Principle. Actually it is an example of inertia. (Sometimes called the water hammer effect to a plumber. ) The rubber mallet comes down and hits the bottle. Bottle lurches downward. The water remains in place. A partial vacuum forms between the bottom of bottle, called the "punt," and the water. This space is filled with a low pressure water vapor. The hand holding the bottle stops the bottle and water in the bottle is accelerated downwards into the punt. It is accelerated by the difference in pressure between the space above the punt and the neck of the bottle. The water drops like a brick into the punt. Sometimes you can even hear the clink sound when it hits. When the water hits the bottom the punt pops off because the weakest seam in the bottle's construction is where the punt is attached to the glass.

  Here is high speed video from YouTube that shows this happening.

The video is from the television show TimeWarp and is located here, http://www.youtube.com/watch?v=cOeNxkksruo

These guys are not science teachers and are not practicing safe techniques. Do not hit the bottle with your hand. Use a rubber mallet.