When viscous fluids such as honey dribble onto a surface, they coil around like a self-weaving basket. All you have to do is pour some honey onto toast and marvel at the strange patterns that result. If that whets your appetite (for science), it is easy to do more elaborate experiments and observe the variety of ways that liquids coil. Collect the following equipment:
- 1 liter of viscous honey or sugar syrup
- 1 empty half-liter plastic bottle, with its screw cap
- A drill to make a hole in the cap
- 1 pan
- 1 glass with a flat bottom
- A small quantity of wax or putty
In addition, the following equipment will help you take measurements:
- 1 Webcam or cell phone
- A stack of thin books, about 20 centimeters high
- 1 ruler
- 1 kitchen measuring cup
- 1 watch
- Graph paper or a computer program for drawing x–y graphs
- Computer movie software that allows frame-by-frame advance
As a fluid, a thick sugar solution such as honey or corn syrup works well. Choose the most viscous (thickest) honey or syrup you can find in the supermarket (without going to the extreme of nearly solid honey that has to be spooned out). As a test, tilt the jar quickly by 45 degrees or so; the honey or syrup should take around 10 to 15 seconds to adjust to the jar’s new orientation.
To control the flow of the fluid use a plastic bottle with a screw cap. Cut off the bottom of the bottle and drill a hole with a diameter of about three millimeters (roughly one-eighth inch) in its cap. Hang this unit upside down using string from a dish drying rack or other support so that the cut-off end of the bottle is facing up.
To form the surface on which the fluid will coil, slide the pan beneath the container and place the glass upside down in the pan, directly underneath the hole in the bottle cap.
To start the experiment stop up the hole in the cap using a piece of wax or soft putty. Fill the bottle very nearly to the top with the syrup. When you are ready, remove the wax or putty to start the fluid flowing. If the syrup does not flow in a steady stream, widen the hole in the cap. Keep adding syrup to the bottle to maintain a constant level, which is important to ensure that the syrup flows at a steady rate.
Once you have gotten some practice with the setup, you can begin to make some measurements. Use a Webcam or cell phone to take movies of what happens on the flat bottom of the upside-down glass, making sure to capture at least 10 turns of the coiling rope. Repeat the process for different values of the fall height H (the distance from the hole in the cap to the glass), which can be adjusted by sliding books under the pan. Measure H with a ruler each time you add or remove a book.
To measure the flow rate, replace the glass with a kitchen measuring cup and record the time required to fill it to a certain level.
To determine the coiling frequency for a given value of H, advance the movie frame by frame on your computer and count the number of frames required for the coiling rope to a make some fixed number (five to 10) of turns. Divide the time elapsed by the number of turns to get an estimate of the coiling period T. The frequency f is then just 1/T. You can then plot f as a function of H, either by hand on graph paper or using plotting software on your computer. We recommend making measurements at a dozen different values of H, so you can see the patterns that emerge.