Make Your Own Tornado

The Basic Concepts
Fluids – liquids or gases (vapors) – flow within the vessel that contains them. Tornados, hurricanes, and whirlpools all have the same sort of motion. In these natural cases the rotation is caused by pressure differences. In this project the rotation is caused by the bottle and the impeller. An impeller throws fluids outward. Propellers throw fluids forward or backward.

Bottle with lid (big is better)
Hobby motor, 1.5-3 volts
2 wires, thin, with insulation
Large plastic cup
Food coloring (or liquid watercolor)
Small pieces of Styrofoam packing
Baseboard Aluminum foil
Film canister (no lid necessary)
2 C batteries
Resistance wire

Rasp or coarse sandpaper (to roughen up the cap)
Wire strippers

Build It!

Make a 19/64-inch hole exactly in the middle of a bottle cap.

Scratch the top of the cap with a rasp so the glue will stick to it better. Then put glue around the hole and press the motor firmly into the hole. Add more glue around the joint between the cap and the motor so that it is very strong. It is important to get this right the first time, because it will not glue well after it gets wet. But be careful not to get any glue inside the cap, on the turning shaft.

Strip both ends of two wires. Connect them to the motor.

Cut at least 1 inch of a hot glue stick. Drill a hole in the end of it with a small nail bit. Cut a slit into the other tip of the glue stick.

Cut a tiny piece of plastic either from the base of your cup or from another bottle, and insert it into the slit. This is the impeller. Push the motor shaft into the hole at the other end of the glue stick.

Fill the bottle about three-quarters full with water. Add a bit of food coloring- too much and you can’t see the tornado inside the bottle. A bit of glitter and tiny pieces of Styrofoam are interesting too.

Tightly screw on the cap (with motor attached)

Check out your cup and bottle sizes. Make sure the bottle will sit nicely, cap-and-motor-end down, on the cup, without the motor touching the baseboard. For 2-liter-bottle tornados, often the mouth of the cup works to support the bottle, and the cup is glued to the baseboard right side up.

Put a piece of aluminum foil around one end of one wire. Jam the aluminum foil and wire into the bottom of the film canister and glue the film canister to the baseboard.

Tape two batteries together end-to-end and slide one end of them inside the film canister.

Touch the other wire to the top of the batteries and the tornado should begin.

To change the speed of the tornado, connect a piece of resistance wire to the free insulated wire. For full speed, connect the free wire straight to the battery without using the resistance wire, causing the electricity to pass through a bit of it. The more the resistance wire the electricity needs to pass through, the slower the motor will go.

More to Think About and Try

• How could you make the tornado spin faster?
• What would happen if you fill the bottle with water so that there is no air in it?
• What would happen if you put the impeller and lid on a different sized bottle?
• Consider a tiny piece of glitter swirling in the tornado: what is its path through the bottle as the tornado spins?

A Little Background

A battery powers this tornado. The sun powers real tornados and all weather patterns. Radiation from the sun warms the Earth differently according to many factors, such as reflectivity of the surface and cloud cover. Hot areas and cold areas then lead to different air pressures. Wind is basically air moving from high to low pressure, and the greater the difference, the stronger the wind. Hurricanes and tornadoes are special situations where a local area of very low pressure (a large area for a hurricane and a small one for a tornado) becomes the center of strong rotating winds.

Why do the winds blow around in circles? Rotation is a common, stable situation in nature. For example, all know planets and their satellites are rotating. For another example, try to shake a bottle of water or soda from side to side, and then hold it still. Invariably, the liquid is rotating when you finish. In technical terms, the winds of hurricanes and tornados are merely conserving their momentum, as all things must.