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The information below is intended to provide a description of the demonstration, an explanation for elementary students, and further explanation for high school students.

Please keep in mind that not all demonstrations are presented at each show.

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For additional information on uses of liquid nitrogen, please click here.


LIQUID NITROGEN

Figure I. Figure II. Figure III.


Figure IV. Figure V. Figure VI.


Figure VII. Figure VIII. Figure IX.


Figure X. Figure XI. Figure XII.

Description

Equipment: Container of liquid nitrogen
Copper tube, welded shut on one end and wrapped with pipe insulation to facilitate handling
Regular cork
Large pyrex dish
Styrofoam mat
Large balloon (inflated)
Dewer flask
Piece of rubber cut into knife shape
Racquetball
Orange
Styrofoam block
Block of wood and nail

Step 1: The properties and dangers of liquid nitrogen are discussed with the audience. The demonstrators also warn the audience not to touch anything unless a demonstrator says that it is OK. Some of the liquid nitrogen is poured into the copper tube. A cork is placed on the open end of the copper tube and after a few seconds the cork pops off, flying quite a distance into the air. (See Figure I., Figure II.)

Step 2: The large pyrex dish has been placed on a thin sheet of styrofoam (which serves as a mat). Some of the liquid nitrogen is poured into the pyrex dish. (See Figure III.) Water vapor flows away from the liquid nitrogen. The water vapor looks exactly like steam, but instead of rising, the water vapor falls. The demonstrators ask the audience how they might get a large balloon into a small container. After some discussion, a large balloon is placed in the liquid nitrogen and more liquid nitrogen is poured over the balloon. The balloon slowly shrinks and is eventually small enough to be placed into the container (a small dewer flask). (See Figure IV., Figure V., Figure VI.)

Step 3: Several objects are then put into the dish of liquid nitrogen: a flimsy piece of rubber shaped like a knife, an ordinary racquetball, and an ordinary orange. These objects will be allowed to sit in the liquid nitrogen for several minutes. (See Figure VII.)

Step 4: After a few minutes, the demonstrator removes the piece of rubber from the liquid nitrogen (using tongs and special gloves). The once-flimsy piece of rubber is now very rigid and is stabbed into the piece of styrofoam. The rubber knife sticks easily into the styrofoam! (See Figure VIII.)

Step 5: The demonstrator then removes the racquetball from the liquid nitrogen (again using tongs and special gloves). Instead of being bouncy like before, the racquetball is now very hard. When the demonstrator tries to bounce the racquetball, it shatters on the floor in many pieces! (See Figure IX.)

Step 6: The demonstrator now removes the orange from the liquid nitrogen. The orange, which was a little squishy before, is now very rigid. It is so rigid, in fact, that the demonstrator can use it as a hammer, hammering a nail into a board! (See Figure X.)

Step 7: Finally, the demonstrator asks the audience what they think will happen if the large balloon is taken out of the dewer flask. After some discussion, the balloon is removed and placed on the table. The balloon slowly begins to grow larger! After some time, the balloon will regain almost its original size. (See Figure XI., Figure XII.)

Description

Basic Ideas: A gas exerts pressure on all sides of the container which holds the gas. The amount of pressure is related to the energy of the gas and the amount of gas. The higher the energy, the more pressure is exerted, and the more gas is contained, the more pressure is exerted.

When two objects of different temperatures are put in contact with one another, there is an exchange of thermal energy. This exchange, known as heat conduction, causes the warmer object to cool and the cooler object to warm.

Cooling a solid only lowers the temperature of the solid, the solid will not change states. The solid will, however, become more rigid.

Cooling a liquid to its freezing point changes the material to a solid state. This process is known as freezing.

Cooling a gas to its condensation point changes the material to a liquid state. This process is known as condensation.

Heating a solid to its melting point changes the material to a liquid state. This process is known as melting.

Heating a liquid to its boiling point changes the material to a gas state. This process is known as boiling.

Heating a gas only raises the temperature of the gas, the gas will not change states.

Step 1: When the liquid nitrogen is placed in the copper tube, the nitrogen immediately begins to warm up. Some of the copper tube's thermal energy is transferred to the nitrogen. As the nitrogen warms up, it begins to boil: some of the nitrogen particles are changing from liquid form to gas form. Since a gas exerts a much greater pressure on the sides of its container than a liquid does, the amount of pressure inside the copper tube is constantly increasing. To relieve this increased pressure, the gas inside the tube is constantly being forced out the open end of the tube. When the cork is added to the open end of the tube, the gas is cut off from leaving. The pressure inside the tube builds until the force on the cork is so great that the seal is broken and the cork goes flying off.

Step 2: When the liquid nitrogen is placed into the pyrex dish, water vapor flows away from the liquid nitrogen. Instead of rising like steam, however, the water vapor sinks. When the water in the air is exposed to the extremely cold temperature of liquid nitrogen, the water molecules freeze. These frozen water molecules appear as water vapor. Since they are at a lower temperature than the rest of the air, the water vapor sinks.

Originally, the balloon is filled with air, which is in gas form. When the balloon is exposed to the liquid nitrogen, some of the air's thermal energy is lost to heating the liquid nitrogen. This loss of themal energy cools the air inside of the balloon. Eventually, the air inside of the balloon is cooled so much that some of the air's particles condense into liquid form. Since the pressure exerted by a liquid on the sides of its container is much less than the pressure exerted by a gas, the balloon now has a much smaller pressure inside of the balloon. This causes the balloon to shrink. Eventually, it is small enough to be placed in the dewer flask.

Step 3: During this step, nothing exciting happens. The rubber knife, racquetball, and orange are all placed in the dish of liquid nitrogen.

Step 4: When the demonstrator removes the rubber knife from the dish, it is immediately clear that the rubber knife has changed. It is now very rigid. When the rubber knife was exposed to the very cold temperature of the liquid nitrogen, some of the rubber knife's thermal energy was transferred to the liquid nitrogen. This caused the rubber knife to cool. As the rubber knife cooled, the particles of rubber were slowed down, allowing the chemical bonds between the rubber molecules to become much more rigid. Therefore, when the rubber knife was removed from the liquid nitrogen, it was much more rigid.

Step 5: Exactly as in the step before, but with the racquetball instead of the rubber knife, the racquetball has been cooled. This caused the racquetball to become much more rigid. The racquetball was so rigid, in fact, that the force of impact when thrown on the floor was enough to shatter the racquetball.

Step 6: As in the previous step, the orange has become more rigid as it has cooled. It has become so rigid that the demonstrator can hammer a nail. It is interesting to note that not only has the solid particles of the orange become more rigid, but the liquid particles have also frozen to make the orange even more rigid. In the previous steps, the entire rubber knife and racquetball were entirely solid prior to being placed into the liquid nitrogen. In this example, part of the orange was originally liquid.

Step 7: When the demonstrator takes the shrunken balloon out of the dewer flask, the exact opposite of what happened in Step 2 is happening. This time, the air inside of the balloon is very cold and is in liquid form. When the cold particles of air are exposed to the room temperature, there is an exchange of thermal energy. The air inside of the balloon is gaining energy. Slowly the particles of air begin to boil, changing from liquid state to gaseous state. Since the pressure exerted by a gas on the sides of its container is much greater than the pressure exerted by a liquid, there is an increase of pressure inside the balloon. This increase in pressure causes the balloon to expand.

Description


Related Topics

The following physics topics are discussed during this demonstration:

Sponsored by the Physics Department and the Center for Science, Mathematics, and Engineering Education -- University of Virginia