Solve the Problem of Spilled Drinks with Physics!

The SpillNot is an ingenious gadget that will let you carry an open beverage without spilling it. With a little bit of practice, spin a cup of liquid around in a circle without even losing a drop! The forces in action will fascinate your students and challenge their analytical reasoning.

The SpillNot employs simple physics in keeping your coffee cup from spills and breakage. By carrying the moving cup containing liquid, several forces act on the cup, and consequently on the liquid contained inside. If balanced forces are applied to a cup of liquid (…whether at rest or moving with a constant velocity), the liquid remains virtually undisturbed. However, once an unbalanced force is applied to the cup (ex. A force greater to the right than to the left), the cup will accelerate. The liquid’s mass will not accelerate with the cup due to its fluid nature; instead, accelerating the liquid will cause the liquid to spill out of the cup; due to inertia and the liquid’s inability to keep up with the accelerating cup.

The SpillNot’s unique design also allows the liquid to stay within the cup due to forces associated with circular motion. By holding the SpillNot by the strap, the force on the cup and contained liquid is always directed toward the strap. Any movement of the SpillNot is now of a circular nature and the forces on the cup and its liquid are directed toward the center (the strap) of the circle which demonstrates Centripetal Force. The same force which holds a rider on a rollercoaster in an upside-down loop or in swinging a bucket of water over your head is employed by the SpillNot. The accelerating liquid will stay in the cup due to Centripetal Acceleration, now determined by the Centripetal Force on the cup/liquid. Both are directed toward the center of the circular path.

WARNING: Please be aware that swinging the SpillNot with an open beverage does involve some risk of spilling. Best attempted outdoors first using a paper cup.