The thermometer and the calendar both agree: it’s summer. And as you lie in your hammock listening to whine of the mosquitoes, certain questions about summer may float to the surface of you otherwise placid mind. For instance:
What causes sunburn and tanning?
Red skin is inflamed skin, and inflammation is the body’s effort to speed the healing of damaged tissue by rushing more blood to the area. Fifteen percent of the sun’s energy reaches us as invisible ultraviolet radiation, which is powerful enough to penetrate the surface of the skin and cause damage to the skin’s cells. The body tries to keep this from happening by increasing the production of melanin, a brown pigment that resists the penetration of ultraviolet radiation.
Why do boats float?
The scientific principle behind all floating objects is Archimedes’ Principle, named after the famous Greek philosopher who thought of it in the bathtub and ran naked down the street yelling “Eureka!” An object floats if the amount of fluid it displaces matches its weight. The more heavily laden the boat, the deeper it sits, because it has to displace that much more water.
How does swimming work?
The human body is two-thirds water, and therefore its density is very close to that of water. This gives us a kind of neutral buoyancy: we float, but only when we’re almost completely submerged, so part of the trick of swimming is getting your head above water often enough to grab a quick breath.
Swimming strokes are based on the fact that when you push your hand through the water, the water resists. This turns your arm into a lever, with its fulcrum in the water. Applying force to the arm levers your body forward at the shoulder.
How is old-fashioned homemade ice cream made?
Good old homemade ice cream is frozen by putting a mixture of milk, sugar, flavoring and other ingredients (depending on the recipe) in a tub and rotating it in a bath of salt and ice while a paddle keeps the mixture stirring.
Salting the ice makes the resulting ice water colder. Ice water is in a state of equilibrium. Some water molecules from the ice break free, while other molecules in the liquid attach themselves to the chunks of ice. If more molecules break free than attach, the ice melts; but until all the ice has melted, the temperature of the ice water remains the same: 0 degrees.
To break free from the ice, a molecule requires energy. As salt dissolves in water it breaks into charged particles (called ions) that prevent molecules in the liquid from attaching to the ice, but don’t interfere with molecules breaking free from the ice. These molecules get the energy to break free from the surrounding water and ice, which makes the temperature of the mixture drop. Because the salt acts as an antifreeze, the ice continues to melt, making the ice-salt-water mixture colder and colder, until a new equilibrium is reached 10 degrees below freezing–a good temperature for making ice cream.
The sugar within the ice cream mixture also acts as an antifreeze. As the water in the mixture freezes, the concentration of sugar in the remaining liquid increases, which drops its freezing point lower and lower–eventually, lower than the temperature of the ice-salt mixture. As a result, the ice cream never freezes completely solid.
Constantly stirring the mixture insures that the ice crystals that do form don’t grow too big and the ice cream chills uniformly. It also whips air into the ice cream, which increases its volume and also helps keep it soft.
Why do we sweat?
Sweat comes from millions of tiny glands in our skin. Sweat glands respond to excessive heat by secreting a salty, watery fluid. As this fluid evaporates from the skin, it cools the blood rushing by just underneath the surface of the skin in the tiny blood vessels called capillaries. This cooled blood is then re-circulated through the body, where it picks up more heat that it gets rid of again the next time it passes through the skin’s capillaries. If we didn’t sweat, we could easily overheat to a dangerous degree: in fact, one of the symptoms of heat stroke is a shutting down of the sweat glands.
I leave the further search for summer enlightenment with you. I suggest something cold to drink and a cool place to recline.
You might also try closing your eyes.
