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Holes

An Explorit "Science Bytes" article by Evelyn Buddenhagen (1992)

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EXPLORE THE SUBJECT OF HOLES

by Evelyn Buddenhagen (1992)

Lao Tzu was a Chinese philosopher who used the significance of holes, or, rather the emptiness of contained space, as a metaphor for life values. Little did he know that this science center would use it as an exploration topic!

Holes? Why Holes?

"Holes," as a topic, tickles one's mental fancy. It pulls us this way and that, leaping from one example to the other, to look at ideas that are not packaged in chapters in textbooks, or course outlines. It calls upon that delightful component of problem-solving, the search for patterns or isomorphic sets, that is at once playful and purposeful. Making meaningful connections among isolated bits of information is the stuff of science and technology and, therefore, science centers.

Hence, Holes!

A hole by any other name evokes images that make the set seemingly disparate, but, they can be clumped into tidy new packages of likenesses. What images do these evoke?

holes and hollows

caves and coves

perforations and ponds

ghettoes and gouges

pockets and pit holes

holes in atmospheres and holes in arguments

craters and cavities.

Each word calls up a different image because it names a specific thing. They are, however, all related by their reference to some unfilled space in what would otherwise be a solid or whole body. That unfilled space and that solid body could be very large or very small. It could be liquid, solid, gas, or even a social structure. It could even be a colorful and graphic metaphor. It could be a permanent hole, or a temporary one. It could be created by Nature, or through the purposeful or accidental activities of Man.

Most of the holes in the above list are common ones that Nature created. There are other kinds of holes created by Nature that are usually unseen, but not unknown. Some of us know something about them and what they do, but we may not know that they fall into this broad topic of holes.

How are these holes created? Do they serve some purpose or function? What role do they play in the nature of things?

The raison d'etre of one hole probably differs from another. Some may simply be an end-product of a process such as erosion, a disturbance, or a pressure. Geology provides numerous examples in geodes, limestone caves, meteor craters, mining pits, and volcanic craters.

The human body is full of purposeful holes. The cup-shaped fovea that holds 4,000 cones to provide the eye's sharp focus is one such example. Another example is the elegant, minute structure of bone tissue.

Other holes in the body stimulate tremendous efforts to eliminate them. Dental caries, pitted scars in the skin left behind after smallpox has struck, unsealed passageways in the newborn's heart, and cavities in arthritic bones are all examples of highly undesirable holes.

Largely theoretical, holes in solid-state physics refer to the absence of an electron from an atom in certain substances, such as beryllium. Electrical currents move by the motion of these holes.

Some holes are functional, elongated passageways, rather than punctuated voids in solids. In this group are tubes that transport or allow the passageway of busily moving substances. Short, constructed tubes provide shelter for fragile caddis fly larvae.

There are holes that serve as doors or mere openings through which things pass. Stomata are microscopic pores that are part of the epidermal layer of leaves that allow the passage of oxygen, carbon dioxide and water vapor. Millipore filters are precision tools that use the size of the pores or holes to permit certain sizes of substances to go through or be retained. They are used by microbiologists to selectively separate bacteria from solutions as a means of sterilization.

There are highly functional holes in sieves, screens, gauzes, textiles, nets, skin pores, bread, and contact lenses! As discrepant as this set appears to be, there are some common functions. What are they?

Certain objects have holes that enhance their use. Consider a coffee mug, or a pair of scissors. There are specially designed scissors without holes for people with carpal tunnel syndrome, arthritis, or other hand disorders. A special mechanism is used to open and close the scissors.

 

Projects to try at home.

l. Mystery hole

Pour some melted butter into a small, narrow container until it is filled to the brim. Refrigerate until the butter has re-solidified. What do you notice? What do you think happened?

 

2. Holes and filters

Muddy water can be cleaned through a series of filters that have "holes" of different sizes to screen out different sized particles. Make a slurry of water and soil containing organic matter and small pebbles or sand. Filter the slurry sequentially through a series of filters ranging from coarse to fine:

a. kitchen sieve

b. a large funnel lined with coffee filter paper and containing three layers of filtering material with crushed charcoal on the bottom, fine sand in the middle, and fine gravel on the top.

The filtered water is not clean enough to drink but the large particles have been removed. Filters with finer holes are necessasry to remove the smaller bacteria.

 

3. Holes and water pressure

Cut the top off a 2-quart plastic bottle. Make four holes in it with a nail.

Place a strip of a plastic grocery bag l" wide and long enough to extend beyond the height of the bottle. Stand the bottle in a large container. Fill the bottle with water with the plastic strip in place to cover the holes. Pull out the plastic strip and observe the results. What do you notice? What conclusions can you make about the relationship between the pressure of a liquid and depth?

 

4. Quick exits

(a) Fill a gallon plastic jug with water until it is about 4/5 full and close the opening with your hand. (b) Turn the jug upside down over a plant that needs to be watered. (c) When the water is relatively still, remove your hand and watch what happens. Repeat steps a and b. Now, rotate the jug until you can see the water moving in a vortex. Now remove your hand and watch what happens!

 

5. Making craters

In a large baking pan, prepare a l/2 inch layer of flour over an inch layer of sand. Over the flour layer, add a thin (about l/4 inch) layer of fine sand. Drop marbles or pebbles onto the surface from different directions and have someone else figure out the direction that you threw the objects by examining the impact trails of the flour.

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