Objects (Level 5)

This aquarium thermometers is made from thermochromic liquid crystals. Thermochromism is the term used to describe changes in color due to changes in temperature at temperatures for which the object is not burning (that is incandescence!). In the case of these thermometers, the color changes are correlated with the temperature of the liquid crystal to create a useful, inexpensive, and compact thermometer. The liquid crystals in the thermometer strip change their physical properties with temperature and this results in a change in the colors of light they reflect. In general, as a liquid crystal is heated, the reflected light progresses through the spectrum from red, through orange, yellow, green, and cyan, to blue. These color changes, in combination with optical filters or temperature calibration, can be used to construct a thermometer. Alternatively, a thermometer can be created by using slightly different liquid crystals to indicate each specific temperature. I made this sequence of pictures by putting the thermometer on a vase of hot water and gradually adding ice cubes to lower the temperature as I took pictures.

How Does a Mood Ring Work? What do the Colors Mean?

If by "work" you are wondering how they tell your mood, then they simply do not work at all! They are fun and they do change colors. However, they are simply liquid crystal thermometers that you wear on your finger. So they do indicate a change in your body, but that change is actually the surface temperature of your finger. Mood rings are filled with a liquid crystal just like the aquarium thermometers described above.

Specifically, these materials are known as thermotropic liquid crystals and they change with temperature in ways very similar to how the liquid crystals in your LCD computer display or television change when an electrical current is applied to them. For mood rings, the system of glass and liquid crystal material that makes up the ring is calibrated to be a green for an average surface body temperature of about 82° F (28° C). As the ring-wearer's skin temperature increases, the liquid crystal changes toward blue and, as the temperature decreases, the ring changes toward black.

The standard interpretations of the colors of mood rings are:

•Dark Blue: Happy, Romantic, or Passionate
•Blue: Calm, Relaxed
•Blue-Green: Somewhat Relaxed
•Green: Normal
•Amber: Nervous, Anxious
•Gray: Very Nervous
•Black: Stressed, Tense

You can see that these moods might correlate somewhat with your body temperature, but not always. It is entirely possible that a person could be very happy and very cold and then the mood ring would be completely incorrect. So really the colors mean nothing about your mood, but do tell you something about your finger's temperature.

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Ever wonder ... What is the meaning of different colors?

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Updated: Apr. 19, 2011