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Background Information for Science Surprises - Part 2

Cryogenics

What are cryogenics and cryology?

Cryogenics and cryology represent a branch of physics that studies very low temperatures and their effects. The prefix "cryo" comes from the Greek word "kruos," which means extreme cold. The suffixes "genics" and "logy" come from the words for "producing" and "study" ( methodical). When you put them together, you get the words "cryogenics," and "cryology," the production of very low temperatures and the study of their effects.

In outer space, things may get very hot, then very cold. This is an important factor in the design and choice of materials for spacecraft.

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 How do the following substances respond to very low temperatures?

 Metals :

Spaceships are made with several different kinds of metal, so it’s important to know how metals react to extreme cold.

Metals contract when they are cooled. In other words, they take up less space. Some metals will contract more than others at a given temperature. This is demonstrated by a bimetallic strip, which is made of two different types of metal (such as copper and zinc) stuck together. When a bimetallic strip is exposed to temperatures lower than those of room temperature, the strip will bend. This occurs because one of the metals contracts more than the other at the particular temperature. The strip will bend in the direction of the metal that contracts the most (copper in the case of the copper-and-zinc bimetallic strip).

This illustrates that interactions between certain metals can render them unsuitable for spacecraft construction. For example, a copper door in a zinc doorframe would endanger the lives of the astronauts in space, because the extreme temperatures of outer space would affect the tightness of the door’s fit.

Rubber :

Here on Earth, machines often have rubber hoses, seals, gaskets and tires. Rubber at room temperature is very flexible. However, when rubber is subjected to extreme cold, it loses its elasticity. In other words, it becomes hard and rigid. It will no longer bend if you apply pressure to it. Instead it may break. Therefore, in outer space, materials other than rubber must be used.

Gases :

The air we breathe is also curiously affected by exposure to very low temperatures. Air condenses as it cools, meaning it goes from a gaseous to a liquid state. This is well demonstrated by placing an inflated balloon in a very cold environment. The air inside the balloon liquefies. Because there isn’t any more gas in the balloon to exert pressure on the balloon’s walls, it collapses. We are left with a shrunken balloon with a small amount of liquid inside. This liquid is liquid air.

When the balloon and its contents come back in contact with warmer temperatures (room temperature), the air in the balloon expands, returning from a liquid to a gas. Air in a gaseous state can once again exert pressure on the balloon’s walls, and the balloon returns to its original size and shape.

A substance that is a gas at room temperature has a relatively low boiling point; it has enough energy to vaporize at temperatures below about 20 degrees Celsius. Nitrogen gas makes up 78% of the air we breathe. Nitrogen freezes at -210 degrees Celsius and boils at -196 degrees Celsius. Therefore, it is a gas at room temperature. A container of liquid nitrogen indoors will be boiling; if its temperature is measured, the thermometer will read -196 degrees Celsius. Immersing any object in liquid nitrogen will cool that object very rapidly.

There are many applications of liquefied gases in the world today. Liquid oxygen is used in the production of steel and as a rocket propellant. Liquid hydrogen is used as fuel for spacecraft. Natural gas is liquefied for ease of transport. Liquid ethylene is used in the plastic industry. Liquid argon is used in electronics.

Living tissue:

The effect of extreme cold on the human body is well demonstrated by plant matter. If a piece of lettuce or a flower petal is exposed to very low temperatures, it will become brittle. Living tissue in this state can be easily crushed or shattered.

The effect of extreme cold on the human body is well demonstrated by plant matter. If a piece of lettuce or a flower petal is exposed to very low temperatures, it will become brittle. Living tissue in this state can be easily crushed or shattered.

Living tissue is composed mainly of tiny cells. These cells contain a lot of water. When vegetable material is immersed in a very cold environment, such as liquid nitrogen, the water in the cells freezes rapidly. The water then solidifies and expands. The implications of this can be easily seen. A sealed container of water left in the freezer breaks because the water expands.

A similar occurrence results for living tissue at the microscopic level. When living cells are frozen very rapidly, the water in the cells solidifies and expands. This expansion, together with the formation of sharp ice crystals, causes the cell walls to rupture.

To avoid this type of problem, spacesuits are made in seven different layers, partly to handle the high and low temperatures that could be felt in space.

Are there any practical uses for freezing living tissue?

If an antifreeze agent such as glycerol is added to the cells before freezing, one can lower the temperature at which the cells’ water freezes and control the rate of freezing. This helps to prevent ice crystals from forming outside the cell. In this way, cells can be preserved for extended periods of time. If properly thawed, the cells will regain their functions. Problems increase considerably when one attempts to cool large cell masses. It becomes more difficult to control the cooling rate, and antifreeze additives may not reach cells on the inside of the cell mass in sufficient quantities. Furthermore, cells may suffer from oxygen deprivation. As a result, the long-term preservation of people and their limbs and organs is not yet feasible.

Nevertheless, there are a number of applications in the preservation of small cell masses. One of the earliest uses in the 1950s was the freezing of cattle sperm for the purpose of artificial insemination. Sperm can be stored in this manner for years. This technique provides a means for the spread of high-quality breeding stock to all parts of the world.

Scientists freeze micro-organisms used in the production of cheese. It is also possible to freeze pollen from various plants so that cross-breeding experiments may be carried out on plants not usually found together. The freezing of biological cultures assures a continuous supply for experiments.

The preservation of whole blood or separated blood cells is among the most useful of applications. Blood refrigerated in the conventional way keeps only 21 days. After this time it must be processed. The plasma is kept, while the white and red blood cells are discarded. Storage in liquid nitrogen, however, permits the build-up of large stocks needed to cope with catastrophes, as well as the storage of uncommon blood types. A person can build up a supply of his or her own blood. Most apparatuses use liquid nitrogen for blood preservation, as it is convenient, biologically inert, relatively cheap and plentiful.

Liquid nitrogen is also used in the preservation of food by means of refrigeration or flash-freezing. The latter method is carried out either by immersing the food directly in liquid nitrogen or by spraying it with liquid nitrogen. The advantages of this are low cost, rapid freezing and low water loss.

Knowledge of the effects of supercold on tissue can be employed in cryosurgery, which is the local application of intense cold for the selective destruction of tissue, using an instrument the size of a knitting needle. This technique is employed to relieve the tremors and rigidity of Parkinson’s disease. Liquid nitrogen is also used (by physicians only) in the removal of warts and cold sores.

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The Van de Graaff Generator / Electricity

< strong>What is electricity?

  1. It is a form of energy, evident from the fact that it runs machinery and can be transformed into other types of energy such as light and heat.
  2. It is invisible. During an electrical storm, we do not see electricity. We observe the air being ionized when the electricity travels through it.
  3. Electricity is created when particles become charged. Some are negatively charged (electrons), some are positively charged (protons). These opposite charges attract; whereas particles with similar charges repel each other.

The nucleus of the atom contains protons (positively charged) and usually neutrons (no charge) around which whirl electrons (negatively charged). An electron is two thousand times smaller in mass than a proton but its electrical charge is equal to that of a proton. Electrons of many elements, particularly metals, are easily knocked off from their parent atoms and can wander freely in the atomic structure. If a state of unbalanced charge exists, these constitute an electric current. When a battery or other electrical source is attached to a wire, it releases electrons into the wire. They bounce against the free electrons in the wire which are repelled because they have the same electrical charge. They go on bouncing against other free electrons down the wire, causing an instantaneous pressure wave. Provided there is somewhere for them to go, such as a lamp or a motor, the electrons flow out the far end.

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What is static electricity?

Static electricity is electricity at rest. It is produced by friction, by rubbing.

All matter contains positively charged particles called protons and negatively charged particles called electrons. In an uncharged atom, the protons and electrons balance each other and the atom is neutral. If this neutral atom loses an electron, because it has an excess of protons, it is said to be positively charged. If the neutral atom gains an electron, it is said to be negatively charged.

Rubbing can tear electrons loose from certain atoms. Some substances, because of the character of their atoms, tend to lose electrons and become positively charged; other substances gain electrons easily and become negatively charged.

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Why does your hair stand on end at the Van de Graaff generator in the Museum?

The Museum’s Van de Graaff generator removes electrons from the large globe, giving it a high positive charge. If you stand on an insulated plate and touch this globe, all parts of your body become positively charged, including your hair. Since like charges repel, every hair on your head is now trying to get away from every other hair. The best way is to stand straight up. Result - flyaway hairdo!

The Van de Graaff Generator

History of the Van de Graaff Generator

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