Introduction

This fountain demonstrates the coriolis force that twists weather systems and ocean currents on earth.

Material

• A two liter bottle
• A dowel, approximately 20 inches (50 cm) long and 1/4 inch (6 mm) in diameter.
• Tygon tubing, 1/4" or 3/8 " outside diameter.
• Masking Tape, or binder clips to attach the tubing to the dowel.
• Hot melt glue gun
• Drill with drill bit slightly smaller than the tubing. e.g. 7/32" (5mm) drill for 1/4" (6 mm) tubing.
• String, about a meter (3 ft.)

Assembly

Find the center of the dowel and mark it.

Hot melt glue the dowel to the bottom of the bottle. Glue the dowel to one side of the bottom center of the bottle. Allow the glue to harden.

Drill a hole in the bottom of the bottle.

Insert the tubing into the hole. It should be a tight fit. Hot melt glue the tubing into the hole.

The dowel is glued offcenter. The tygon tubing is glued into the tight-fitting hole.

Run the tubing out to one end of the dowel wrap it around the dowel once or twice then turn it back so that it points toward the center of the bottle. Tape the tubing in place.

Use a binder clip to hold the tube to the dowel and to direct the open end back toward the bottle.

Tie the middle of the string to the neck of the bottle.

Finished Bottle.

To Do and Notice

Fill the bottle with water, put the cap on the bottle to stop dripping.

Go outside where dripping water doesn't matter.

Remove the top of the bottle to start the water flow.

Hold the string. Spin the bottle.

Notice that the water that squirts out of the tubing deflects in the direction the dowel is moving.

Reverse the direction of spin on the bottle and notice that the water deflects in the opposite direction.

What's Going On?

The water flow is deflected by the coriolis force.

When the water comes out of the tubing it is moving to the side at a velocity of perhaps 10 cm/s.

As the water move toward the center of the bottle it travels in a straight line. It continues to move to the side at 10/cm/s. However, the dowel closer to the center is moving to the side more slowly. So the water moves ahead of the dowel.

The human eye and brain jumps into the frame of reference of the rotating dowel. In this frame of reference the water stream appears to deflect to the side. (While in the frame of the fixed stars the water is moving in a straight line.) In the rotating frame of reference physicists have to invent a force to explain the deflection of the water, the coriolis force.

So What?

If the dowel rotates counterclockwise when viewed from above then the water deflects to the right.

The earth rotates counterclockwise when viewed from above the north pole. The coriolis force deflects ocean currents and air masses to the right as they move.

Credit

I first saw the coriolis fountain exhibit at the museum "Tom Tits Experiment" in Stockholm Sweden where it was created by Klas Fresk.

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Scientific Explorations with Paul Doherty

© 2003

1 November 2003