Inertia - Chalk in the Bottle Trick Akin to pulling a table cloth out from under a table setting. email to friend
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The purpose of this project is akin to that of pulling a table cloth out from under a perfectly set table (dishes, glasses, silverware, etc.) It shows that if an object has mass it has inertia (a resistance to changing its motion). In other words, the dishes stay put because of their mass.

Materials

- A wooden hoop (an embroidery hoop works great, about 8-10")
- A 1/2" piece of chalk
- A test tube
- A flask

Experiment
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Place the test tube inside the flask so that a portion of the test tube is outside the flask. Tape the test tube in place. Balance the bottom edge of the embroidery hoop on top of the test tube. Place a piece of chalk on top of the embroidery hoop so that it is in line with the test tube. With a quick action, pull the embroidery hoop off of the test tube with one finger so that the motion of your arm is parallel with the table. Make sure to grab the hoop with only one finger and on the INSIDE of the hoop. If done correctly the chalk will drop directly into the test tube.

Observations

The chalk's position will not move horizontally. The hoop's motion is not enough to move the chalk left or right. If done to slow, or if the hoop is grabbed with even a slight upward motion then the chalk will move horizontally.

How does it work?

Chalk has mass, therefore it has inertia. It has a tendency to resist the horizontal motion of the hoop. When the hoop is gone, gravity is the only force left on the chalk and PLOP, it falls into the test tube.