Vacuum Pack Science

1.  In this experiment, you will need the assistance of two people to help you by either being shrink wrapped or to help you shrink wrap.
2. Have one of your assistants step into the plastic bag feet first.  Have your other assistant help bring the bag up around the shoulders of the person being shrink wrapped.  REMEMBER, NEVER PLACE THE BAG OVER ANYONE'S HEAD.
3. Feed the nozzle of the vacuum cleaner into the plastic bag and have your assistant hold it in their hands.  Remind them not to let the opening of the nozzle suck in their clothes or the bag.  Tell them to use their hands to partially shield the nozzle from their clothes and the bag.
4. Hold the open end of the bag just tightly enough around the back of the assistant's neck to form a seal.  Do not pull too tight, as it can restrict their breathing.
5. Turn the vacuum on and remove the air from the inside of the bag.  In seconds, the bag will mold around the assistant inside of the bag.
6. Ask your assistant to try moving around inside of the bag... it's nearly impossible!
7. Turn the vacuum off and release the seal on the bag.  Now you will see air refilling the bag.

How does it work?

When presenting this demonstration in a science class, students may have the misconception that the air is "sucked" out of the bag. This is a good time to remind students that Newton talked about forces as a "push" or a "pull" and never referred to a motion of "suction." Here are a few important things to remember:

• Air occupies space.  Prior to starting the experiment, the bag was filled with air.
• Before turning on the vacuum cleaner, the air pressure inside the bag was the same as the pressure outside the bag.
• The vacuum cleaner pulled the air from the inside of the bag and created a situation where the pressure outside the bag was greater than inside the bag.  The atmospheric pressure outside then pushes the bag from all sides, forming to the contours of what is contained inside.

In light of your new discovery, explain what happened to your assistant using the terms "push" and "pull" in place of the word "suction."  The practical applications for this experiment include vacuum packaging of food such as coffee and peanuts or cryovac packaging in the meat packing business to reduce spoilage of meats.

Additional Info

Wayne Goates is credited as the creator of this science demo in 1969, and he's been using it to illustrate the dramatic effects of atmospheric pressure. Wayne's original demo consisted of an arm being placed in a small plastic bag to simulate how a sphygmomanometer (blood pressure machine) works and was later expanded to the one with the student's arm being "shrunk." He revived the demo when his wife purchased a plastic bag from QVC that was to be used for storing sweaters and blankets so that several articles could be placed in the bag and the contents could be reduced by pulling the air out of the bag. He explained that she had spent too much money on the bag, and her reply was to come up with something better... and he did.

Reference: Wayne Goates, NMLSTA Level Line.
"Shrink Wrap With A Vacuum," Winter, 1996.