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Ziploc Bag vs Pencil Experiment

This simple experiment to demonstrate the scientific method is always a hit with the scouts. The results are not usually what they expect.

This experiment also fits in well with a Science theme .

Ziploc Bag vs. Pencil Experiment

First step in the scientific method: Define the problem

The problem is: What will happen if I fill a Ziploc bag with water, seal it, and then stick a pencil through it?”

Second step in the scientific method: Make a hypothesis

Have the scouts guess what will happen when they stick the pencil through the bag. Will it make a mess or won’t it?

Third step in the scientific method: Define the procedure

  1. Fill a Ziploc sandwich bag with water.
  2. Seal it.
  3. Stick a very sharp pencil all the way through the bag so that the pointy end is outside of the bag on one side and the eraser is outside of the bag on the opposite side.
  4.  Observe what happens

Fourth step in the scientific method: Collect your data

Give each scout a Ziploc bag and a very sharp pencil and let them each run through the procedure.

Fifth step in the scientific method: Organize your results

Make a chart showing how many scouts made a mess when they put the pencil through the bag and how many did not make a mess.

Sixth step in the scientific method: Arrive at a conclusion

Have the scouts look at their results. What can they conclude? Was their hypothesis correct or incorrect?

Explanation: The water should remain sealed in the bag until the pencil is removed. Plastic is made of long chains of molecules. These are called polymers. This is what makes the plastic in the bag stretch. Putting the pencil through the polymers simply pushes them to the side. Their flexibility allows them to continue to form a strong seal around the pencil.

Warning Don’t pull the pencils back out until you are ready for the liquid to come flowing out of the bag! Do that part over a sink or outdoors!!!!


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