Shrink Wrap Kid
Before you start blasting me with comments… let me explain. This is a very cool science demo, not a classroom management technique (although it might just work). The demo was originated by Wayne Goates, and I saw had the fortune of seeing Bob Becker perform it live at a ChemEd conference years ago. You’ll see why the Vacuum Packed Kid became an instant favorite. Peggy McCall from Houston County, Georgia attended our Science in the Rockies summer workshop in 2007 and immediately took home the idea to share with her 6th grade honors science class. Remember… the bag doesn’t go over the kid’s head – you’re shrink wrapping from the neck down!

The premise of the science demonstration is quite simple… Holding one end of a vacuum cleaner hose, the brave volunteer steps into a giant bag that is pulled up and around the base of the neck (to form a good seal). Remember… the bag NEVER goes over the person’s head! With one flick of the switch, the air is removed and the bag will shrink and mold itself tightly around the contour of the person’s body. It’s great to watch the reaction on the person’s face as he becomes immobilized by a plastic straight jacket (so to speak).

But what does it teach? As Wayne Goates describes, the common misconception is that air is “sucked” out of the bag, but as all good students of science know, Newton never used the word suction in any of his writings. Instead, he used words like push and pull to describe forces. The vacuum cleaner pulls the air out of the bag and allows atmospheric pressure (14.7 pounds per square inch) to push inward on the body of the person inside the bag. Before turning on the vacuum cleaner, the pressure inside the bag was the same as the pressure outside the bag. The vacuum cleaner pulls the air out of the bag and allows the form fitting plastic to tightly mold itself to the person’s body. The pressure inside the bag is less than the air pressure outside the bag. Feeling the effects of this reduced atmospheric pressure pushing on your body is quite amazing.
5 replies
  1. Gary Croniser II
    Gary Croniser II says:

    Where can I purchase the clear bags for this demonstration. I have been able to find white, black, and other colors, but I would really like to find bags like those clear ones used in steve’s demo and in yours. Any help would be greatly appreciated.

    Reply
  2. Wayne Goates
    Wayne Goates says:

    When discussing the Demo, students have the misconception that the air is “sucked” out of the bag.  This may be a good time to remind students that Newton talked about forces as a “push” or a “pull” and did not refer to any “sucking” motion.  As I remind teachers and students alike, the principle involves forces.  It should be pointed out to your audience that prior to turning on the Shop-Vac, the pressure inside the bag was the same as the pressure outside the bag.  When the Shop-Vac was turned on, the pressure inside the bag was reduced and became less than the pressure outside the bag causing the bag to shrink.  Polyethylene in trash
    bags is low density polyethylene ( LDPE ) and the flexible polymer chains permit the bag to be molded to the “student“ package.
    Wayne Goates

    Reply

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