# Teaching with this issue.

Page 8: Electricity ...

BACKGROUND: Lightning is actually a very large discharge of static electricity--the accumulation of electric charges on an object. A review of this concept will enable students to better understand the article.

First, some basics. Atoms are made up of positively charged protons, negatively charge electrons, and neutrons, which have no charge. Atoms are normally electrically neutral, and contain the same number of protons and electrons. Some atoms do not hold their electrons tightly and may lose some of them easily. This contributes to the buildup of static electricity.

Example: When you walk across a carpeted floor, especially when the air is dry, some of the electrons held loosely by the carpet are transferred to your shoes. Your shoes, now with an excess of electrons, are no longer neutral. They now have a negative charge. The carpet, correspondingly, is left with a positive charge due to its deficit of electrons. The excess electrons are stored in your body, giving it an overall negative charge. The accumulation of negative charges in your body is an example of static electricity.

Objects with opposite charges attract (like charges repel each other). Dry winter weather often causes your clothing to accumulate charges. When different items of clothing accumulate different charges they attract one another--they cling.

Charged objects can also cause the electrons of a neutral object to rearrange their positions. As an example, if a balloon that has been charged with a cloth is brought near your sleeve, the added electrons in the balloon will repel the electrons in the sleeve. This will leave fewer electrons near the surface of the sleeve, resulting in a positive charge. The negatively charged balloon is attracted to the sleeve and sticks to it.

The charging of a neutral object by the presence of a charged object, as in the example above, is called charging by induction. Lightning results when negatively charged clouds induce a positive charge in the objects below them. When the difference in these charges becomes great enough, lightning occurs.

For detailed information and diagrams explaining weather of all kinds, you might want to consult USA Today: The Weather Book by Jack Williams (Vintage Books, 1992).

SUBJECT TIE-INS

PHYSICAL SCIENCE: People troubled with static cling solve the problem by spraying their clothing with water or hair spray. Experiment to see if this removes the static from a balloon as well. Try to explain why this is effective.

* Demonstrate a Van de Graaff generator for the class. (One will probably be available from the high probably be available from the high school physics department.) Have a student with long hair place a hand on the globe before starting the machine. A buildup of negative charges will cause the strands of hair to repel one another and stand "on end." Experiment with other materials such as foam packing material, small pieces of paper or aluminum foil, and puffed rice cereal.

* Bring a lighted match near the generator's dome. The match will go out. Ask students to try to explain the phenomenon. (The negative charges ionize the oxygen so that it cannot be used for combustion.)

* Give students a chance to make a tasty lightning flash in their mouths. Give each a wintergreen-flavored candy and a mirror. Have them go into a very dark room or closet and chew the candy while keeping their mouths open and watching in a mirror. (Crushing the candy causes the sugar crystals to break apart, making bits of candy with different electrical charges. A spark will jump between the bits, with the wintergreen oil making it easier to see.)

BIOLOGY: Most people strucky by lightning escape with just a few skin burns. This is because the lightning may not penetrate the skin, instead flashing over the outside of the body. Others suffer major damage to the nervous system. Why does lightning affect the nervous system? (Nervous system is electrical.)

STS: Debate: If lightning started a fire in a national park, should the fire be allowed to burn its natural course, or should major efforts be made to extinguish it? Would opinions differ it the fire was started accidentally by a camper?

MATH: Students can tell how far away a lightning bolt is by counting the number of seconds between the lightning and the thunder and then dividing by three. The answer gives the distance to the lightning in kilometers.

LANGUAGE ARTS: Play a recording of Paula Abdul's 1990 hit song, "Opposites Attract." Ask students to explain what the title means and how it relates to this article. Ask them to bring in recordings of songs that contain references to thunder and lightning.

* Assign students to find the origin of the word electricity in a dictionary. Have them explain the connection between its origin and its present use (electricity comes from the Greek word elektron, meaning amber, which is petrified tree resin. If amber is rubbed with a piece of cloth it develops a charge). Experiment with a piece of amber.

* Challenge students to design print or video ads for lightning safety for airing on local public access stations or for display in public areas such as golf courses and parks.

Page 14: An ocean ...

BACKGROUND: Hydrothermal vents are one of the most exciting areas of exploration and research on the ocean floor. These vents, marked by huge rock chimneys, were discovered about 15 years ago. The chimneys form when cold sea water seeps through seafloor fractures, absorbs heat, dissolves minerals, then bubbles upward again, depositing the mineral in tall solid formations as the superheated fluid mixes with the cold seawater.

Samples taken from areas near vents included blends of sulfur with iron, copper, zinc, and sometimes, gold and silver. The tremendous depth, combined with the pressure cold, and darkness, make mining of these resources something that will take place far into the future. Adding to the difficulty are economic and environmental considerations. A start-up mining operation could cost billions of dollars. Environmentalists fear that mining would destroy the fragile ecosystem near the vents, endangering species that have just been discovered.

Life scientists are excited about the many new creatures found near the vents. Probably most interesting are the many kinds of new bacteria discovered that dwell not only in the other creatures, but deep in the hot vents themselves. Some survive by eating the sulfur compounds found there. An enzyme isolated from one such microbe was found to be useful in manipulating tiny bits of DNA. Now commercially available under the trade name Deep Vent, the enzyme allos scientists to rapidly make trillions of copies of tiny amounts of DNA. (In Jurassic Park scientists used the technique to clone dinosaurs.

SUBJECT TIE-INS

EARTH SCIENCE: To explain how vents form from the sudden cooling of a hot fluid, do the following teaher demonstration (wear safety glasses): Fill a test tube halfway with powdered sulfur. Heat this gently in a vented area until all the powder liquefies. Quickly pour the liquid into a beaker of cold water. A glasslike solid will form, similar in shape to the chimneys at the bottom of the sea.

Free materials for the teaching of earth science are available from the

Geologic Inquiries Group U.S. Geological Survey 907 National Center Reston, VA 22092

Use school letterhead; indicate the grade and subject taught; include a mailing label with your address. Earth science teacheres should request the "Teacher's Packet of Geologic Material." General science, environmental studies, and elementary school teachers should request the "Selected Packet of Geologic Teaching Aids."

STS: Divide the class in half and debate: Should we permit mining at hydrothermal vents or declare these areas biological preserves?

Page 18: Biscuit ...

BACKGROUND: An acid is a substance with a hydrogen atom that can be easily pushed out of its molecules when dissolved in water. Examples of more familiar acids are hydrochloric acid (HCI), sulfuric acid (H2SO4), and vinegar, which is acetic acid (CH3COOH). A base is a substance with an OH radical that can be easily pushed out of its molecules. Examples of bases are ammonium hydroxide (NH4OH), calcium hydroxide (Ca(OH)2), and potassium hydroxide (KOH). Salts form when an acid and a base react to neutralize one another. The salt is a compound consisting of the combination of the atoms left over after the free Hs have detached themselves from the acid and the free OHs from the base. The detached Hs and OHs join to become water. Examples of salts are sodium chloride (NaC1), magnesium sulfate (MgSO4), and copper sulfate (CuSO4).

Use of an indicator is the easiest means to tell if a substance is an acid or a base. The indicator can be a solution like btb, or can be part of paper strips. A base will usually turn and indicator blue, while an acid will produce a red color.

SUBJECT TIE-INS

PHYSICAL SCIENCE: To make a simple indicator to test for acids and bases: Loosely fill a quart jar with uncooked purple cabbage that has been torn into small pieces. Heat one liter of distilled water to boiling and pour it over the cabbage. Allow the jar to stand until the water cools to room temperature. Pour the cooled cabbage solution through a strainer into a second jar. Discard the cabbage leaves. Use the liquid to test for acids and bases. An acid will turn the liquid red and a base will result in a green color. Provide a variety of common liquids for students to test to determine if each is an acid or a base. Vinegar (an acid) and ammonia (a base) would be good examples so that students recognize the color changes.

* Have students experiment to create a neutral solution starting with a basic solution (one part ammonia diluted with three parts water) and an acidic solution (one part vinegar, three parts water). Test combinations with the cabbage indicator. It will remain its bluish color, turning neither red nor green, when a drop or two is added to a neutral solution.

* To make orange soda: Squeeze all the juice from an orange. Add an equal amount of water. Stir in a level teaspoon of baking soda. Taste and add sugar if necessary. The baking soda reacts with the citric acid in the juice to produce carbonation.

* Bring in a small toaster oven or move the class to the homeeconomics room to experiment with recipes that use either baking soda and an acid or baking powder. Enjoy the results (a good way to include a discussion of solutions, mixtures, and other chemistry terms).

EARTH SCIENCE: Geologists can use an acid-base reaction to help identify specimens. If an acid limestone or marble, bubbling will occur. This is because limestone contains a carbonate form of calcium, a base. When it react with the acid, the carbonate leaves the rock to form a salt and carbon dioxide bubbles are released. (This reaction also causes deterioration of the rock, which is why acid rain does so much damage to limestone and marble statues.)

LANGUAGE ARTS: Have students collect recipes that use either baking powder or baking soda and an acid. Combine these into an illustrated recipe book for sale or distribution to classmates and teachers.

Page 22: A matter ...

BACKGROUND: In the fall of 1986, National Geographic Magazine conducted a smell survey. A number of interesting results were reported: Of the six scents presented to the participants (sweat, banana, musk, cloves, gas, and rose), sweat and musk were not detected by a surprisingly large percentage of people. The ability to detect the smell of sweat varied around the world. While 37 percent of American men could not distinguish the smell, only 21 percent of those from Africa did not identitfy it. People who work in factories and offices scored far above average at correctly identifying smells. Those who work outdoors scored below average, but not as poorly as those who claimed they didn't work. Age seemed to have no effect on the sense of smell, but women consistently scored better than men. For a complete summary of the results, see the October 1987 National Georgraphic.

SUBJECT TIE-INS

BIOLOGY: Tracking dogs depend on their sense of smell to follow criminals from the scene of a crime or to help find lost children. Specially trained dogs also are used to "sniff out" drugs, bombs, and people buried in an avalanche or the rubble left by an earthquake. Find out if the trainer of one of these animals is available to discuss with the class how animals are trained and to demonstrate the dogs' skills.

STS: Conduct a serious of taste tests to determinate if students can really discriminate between different brands of cola, potato chips, and similar products. Students must be blind-folded for the tests, or the products must be in unmarked containers, to make the tests fair.

* Natural gas is odorless, but most students will recognize the smell of leaking gas. This is because an odorous substance is added to natural gas so that leaks can be detected. Invite a representative of the gas company to visit class to talk about the safe use of natural gas. Find out if there are any devices available to people who lack a sense of smell to warn them of potential danger.

* Ask students to wear or bring their favorite kind of perfume or cologne to class. Have the boys evaluate and rate the perfumes, while the girls do the same for the boy's cologne. Don't reveal the brand until the testing is complete.

* Pour samples of various fruit-flavored bottled waters into unmarked glasses. Have students hold their noses, take a sip of each, wash is around in their mouths, and note the taste. Then have them release their noses and note any changes in the flavor. Ask when the flavor was most pronounced and have them explain why.

MATH: Graph the results of the hands-on experiment on page 26.

LANGUAGE ARTS: Collect samples of advertisements for perfumes and colognes. Analyze the techniques used to sell these products. Make a bulletin board display of the ads. Since many of the ads contain strips with a sample of the product's odor, write to the advertiser to find out how such strips are produced.