When cohesion is more of a factor, the water forms spherical droplets; when adhesion is more of a factor, we get sheets of water. The wax on the wax paper, it would seem, acts like the oil. When warm air hits the cold surface, it reaches its dew point and condenses. This leaves droplets of water on the glass or can. When a pocket of air becomes full of water vapor, clouds form.
Those flat bottoms are where vapor begins to condense into water droplets. Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Psychological disciplines What is it called when water beads up on a surface?
Psychological disciplines. Ben Davis February 1, What is it called when water beads up on a surface? Carefully done, this phenomenon can also be illustrated with a thin razor blade or a paper clip.
The fact that small droplets of water bead up on surfaces does not mean that water—or any other liquid—does not interact with other substances. Sometimes the attraction can be very strong. Adhesion The tendency of a substance to interact with other substances because of intermolecular forces.
If cohesive forces within a liquid are stronger than adhesive forces between a liquid and another substance, then the liquid tends to keep to itself; it will bead up. However, if adhesive forces between a liquid and another substance are stronger than cohesive forces, then the liquid will spread out over the other substance, trying to maximize the interface between the other substance and the liquid. We say that the liquid wets the other substance. Adhesion and cohesion are important for other phenomena as well.
In particular, if adhesive forces are strong, then when a liquid is introduced to a small-diameter tube of another substance, the liquid moves up or down in the tube, as if ignoring gravity. Because tiny tubes are called capillaries, this phenomenon is called capillary action The behavior of a liquid in narrow surfaces due to differences in adhesion and cohesion.
For example, one type of capillary action— capillary rise —is seen when water or water-based liquids rise up in thin glass tubes like the capillaries sometimes used in blood tests , forming an upwardly curved surface called a meniscus The curved surface a liquid makes as it approaches a solid barrier. Cotton is a good material for this; polyester and other synthetic fabrics do not display similar capillary action, which is why you seldom find rayon bath towels.
A similar effect is observed with liquid fuels or melted wax and their wicks. Capillary action is thought to be at least partially responsible for transporting water from the roots to the tops of trees, even tall ones.
On the other hand, some liquids have stronger cohesive forces than adhesive forces. In this case, in the presence of a capillary, the liquid is forced down from its surface; this is an example of a type of capillary action called capillary depression.
In this case, the meniscus curves downward. Mercury has very strong cohesive forces; when a capillary is placed in a pool of mercury, the surface of the mercury liquid is depressed Figure Responsible car owners are encouraged to wax their cars regularly.
In addition to making the car look nicer, it also helps protect the surface, especially if the surface is metal. The answer has to do with cohesion and adhesion and, to a lesser extent, rust. Water is an important factor in the rusting of iron, sometimes used extensively in outer car bodies. Keeping water away from the metal is one way to minimize rusting.
A coat of paint helps with this. However, dirty or scratched paint can attract water, and adhesive forces will allow the water to wet the surface, maximizing its contact with the metal and promoting rust. Wax is composed of long hydrocarbon molecules that do not interact well with water.
Hydrocarbons are compounds with C and H atoms; for more information on hydrocarbons, see Chapter 16 "Organic Chemistry". These include oils, fats and waxes; all of which are called non-polar substances. When water falls on an unwaxed car, the forces of adhesion are almost as strong as the forces of cohesion, and the water spreads out.
Furthermore, if the painted surface is not perfectly smooth, water can be channelled for some distance along tiny ridges and valleys. This is particularly true if there is dirt on the car. The dirt itself may be charged, and attract water even more. These tiny flaws may not be readily visible without a magnifying glass, but you can sense a rough surface when you run your hand over it. On such a rough surface, drops of water appear flat and wide and often uneven.
Water, out of any compound on Earth, or even in the universe itself, has some of the most unique physical properties. Unlike most materials, when water turns from a liquid to a solid, it expands. This quality is what allows ice to float at the top of water. If ice did not float, all the water on earth would eventually freeze, leaving humanity to die in a frozen wasteland. This property is possible due to the way water molecules interact with each other.
When in its liquid state, water molecules are much closer together. They slosh together and attract each other in much more fluid water than other compounds.
This trait is due to something called hydrogen bonding. Essentially, the single oxygen atom and the two hydrogen atoms are electrically charged in such a way that each water molecule is able to connect very closely and fluidly to the ones around it. This property also causes surface tension, which is why a bit of effort is needed to pierce the surface of water.
0コメント