Engineering for Industrial Designers and Inventors: Fundamentals for Designers of Wonderful Things by Thomas Ask

Author:Thomas Ask [Ask, Thomas]
Language: eng
Format: azw3, pdf
Publisher: O'Reilly Media
Published: 2016-05-04T04:00:00+00:00

Figure 5-4. Nature of temperature

Notice the broad range of molecular energy; remember temperature is an average value. This curve also illustrates the effect of evaporative cooling. As the high-energy molecules to the right evaporate, they lower the average temperature of the remaining liquid phase molecules. This may beg the question of why high-energy molecules are in a liquid state, and the answer can be considered using a magnet analogy. Consider two magnets that are attached. You can separate the magnets by pulling them apart with a force greater than their attraction. This is what happens when molecules vaporize. However, there is a small time when even though the force on the magnets is greater than required, they have not separated. This is the condition of these high-energy molecules—give them time and they will vaporize.

In terms of real molecular surface forces, the attraction between the molecules is developed by the electrical attraction produced by the shape of the molecule. That is, most molecules are not spherical—rather they are all sorts of weird shapes dictated by the element’s orbital shape. Water, for example, is shaped like a “V” with one end having a positive charge and the other end a negative charge. This polarity encourages water molecules to stick together (and makes them easily rotated by microwave ovens!).

Figure 5-5 provides insight into the nature of these three phases and how it relates to surface force adhesion.

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