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Hidden tears, hard water, flat poles

Q: Where does a tear come from? How is it formed? Also, what triggers a tear? Is it the emotions, the soul, or spirit? Is it limited to humans? (John, Albuquerque, New Mexico)

Yes, crocodiles really do shed tears.  (click the picture for a blink). [Adam Britton, http://crocodilian.com]

A: Tears come from two places. First, from tiny glands (called the lachrymal glands), about the size and shape of a shelled almond, located just above the outer corner of each eye. Also, cells in eye membranes make tears — the ones that line the eyelids and cover the exposed part of the eyeball.

These glands and cells constantly form tears. The tears ooze through tiny ducts from the lachrymal glands into the eyelid membrane and thence over eyeball membranes where they flush the eye. That happens all the time, automatically, to prevent eyes from drying, which can harm vision and even lead to infection.

Events (like a fleck of dust landing on the cornea, bright lights shining into the eye, or eating chili peppers) can trigger a tear reflex response. Strong emotions — both laughter and sorrow — can also cause tears to flow.

The brain triggers emotional releases, such as laughing and crying. Perhaps the source of such feelings is indeed the soul or spirit but that’s beyond the realm of science.

Many animals seem to experience sadness as we do. They cry and whimper but few if any spill tears while crying. (A zookeeper, though, once told Charles Darwin that sometimes elephants weep from sorrow.)

Animals do shed tears, however. A crocodile’s third eyelid flushes tears across the eyeball to lubricate its passage and to clean and protect the eye. Birds moisten their eyeballs with tears while flying. An aardvark’s tear membrane protects its eyes against termite bites. Polar bears, horses, and dogs produce tears too.

Further Surfing:

Crocodilians: Natural history & conservation

WonderQuest: Animals cry but don’t weep

WonderQuest: Why we cry

Hard water

Q: I was wondering what the difference is between hard and soft water. Why does it feel "cleaner" after a hard water shower versus soft? I still feel there is soap on me after using soft water. Also, is there any advantage of one over the other? (Jerome)

A: The main difference between hard and soft water is hard water contains much more dissolved minerals — calcium and magnesium, for example — than soft water does.

Pipes carrying hard water, clogged with scale [Kinetico Incorporated]

It’s easier "to get the soap off" after a hard-water shower because you end up with less soap. Calcium and magnesium in the water react with fatty acids in the soap to form a grey soap scum. This uses up some of the soap. It’s easier to rinse off the remaining smaller quantity.

Both hard and soft water have advantages. Hard water has minerals that enhance taste. Soft water, on the other hand, may taste salty because sodium salts are often used to rid the hard water of minerals. Calcium and magnesium found in hard water are good for teeth and bones.

Soft water is easier on heaters, pipes, and plumbing fixtures. Heating hard water precipitates carbonates out of the water. The muck then sticks to the insides of such things as water heaters, teakettles, and plumbing pipes.

In hot-water heaters and boilers, the sticky scales have poor heat conductivity and so transfer heat poorly. Heaters and boilers then use more fuel and waste energy.

The scales also clog pipes.

Flat poles

Q: What is the distance from the center of the earth to the North and South Poles? (Ronald, Rathdrum, Idaho)

A: The Earth’s polar radius (distance from its center to the North or South Pole) is 3950 miles (6357 km).

By the way, the Earth’s equatorial radius is 3963 miles (6379 km). Thus the distance from Earth’s center to its Poles is 99.7% of the distance to its equator. So, Earth isn’t a perfect sphere but it’s close. Earth bulges around its middle and flattens at the poles.

The South Pole where the ice is 9000 feet deep.  [NOAA]

Further Surfing:  Wikipedia: Earth radius

(Answered May 7, 2004)