Pen in a Bottle

An embroidery hoop is balanced on the mouth of a soft drink bottle, and a pen is balanced on top of the hoop. When the hoop is snapped sideways, it moves quickly out from under the pen, which then drops straight down into the bottle. This demo illustrates inertia, where the pen remains in its position due to its resistance to changes in motion and falls directly into the bottle once the supporting hoop is removed. It provides a simple yet effective way to demonstrate the principle of inertia and the concept of objects maintaining their state of motion until acted upon by an external force.