Two Paddles for a Kitchen Mixer

A Mixer for the Cooking Club

A cooking club wants a small mixer for its kitchen drink station. Before using any food, the club will test the mixer with room-temperature water and food coloring. The device must mix 200 milliliters of water until the color looks even throughout. It must finish in 20 seconds or less and leave no drops outside the cup.

The club has one enclosed, low-voltage battery pack, a switch, a small electric motor, a stand, and two smooth plastic paddles. One paddle is narrow, and the other is wide. Each paddle can fasten to the motor’s turning shaft. The stand holds the motor above the cup. A teacher-prepared splash lid has an opening for the shaft. Only these materials may be used.

An adult checks each setup before testing. The battery pack, motor, switch, and wires must stay dry and above the water. Students keep their hands away from moving parts. They open the switch before adjusting the device. They do not taste the test water. With the switch closed and the battery connected, the motor’s shaft turns and makes a quiet hum. With the switch open, the shaft slows and stops.

For each mixing trial, students use the same cup, motor, battery pack, and water amount. They start with fresh water and place one drop of coloring in the center. They lower each paddle to the same depth. One student times how long the color takes to look even. Another counts drops that land outside the cup on a fresh, dry paper sheet. They begin by comparing the narrow and wide paddles without a lid.