Water Jamboree 2006 – April 26 & 27 
 Harlan County Reservoir Nebraska  
 

            On April 26 and 27, 2006 staff from the Hastings Weather Forecast Office participated in the annual Water Jamboree at the Harlan County Reservoir, which was hosted by the Nebraska Natural Resource Division.  WFO Hastings provided a program of six experiments designed to demonstrate principles of physics than can be related to weather.  This program was provided to 12 groups of elementary and middle school students during the two-day event for a total of approximately 300 students and teachers.  This document was produced to share the program that was provided during the event with other WFOs in Central Region. 
 

Piercing a straw through a potato 

In this experiment, students attempt to thrust a drinking straw through a small to medium-sized potato.  In this particular instance, flexible drinking straws were used.  However, non-flexible drinking straws would probably work just as well, and perhaps even better.  The premise behind the experiment is that simply trying to thrust a straw through a potato will yield limited results because straws generally break and crumple when one end of the straw is forced into a solid object.  In the best-case scenario, a straw can be driven a short way into a potato.  The demonstrator leading the experiment makes a suggestion to the students that if one end of the straw is bent, air will be trapped and compressed within the straw when it is thrust into the potato.  This will make the straw quite rigid.  Because of this increased rigidity, and because of the relatively sharp edge of the straw being thrust into a small area of the skin of the potato, the straw can actually pierce through the entire potato.  After the students take a turn at piercing potatoes with their straws, the demonstrator ends the experiment by explaining to the students they have witnessed one tangible effect of air pressure.

 



Sucking an egg into a bottle   In this experiment, the demonstrator states they can force a hard-boiled egg into a bottle without physically pushing it in with their hand. 

Beginning with a seven inch tall glass bottle with a wide mouth, the demonstrator lights 5 or 6 wooden kitchen matches and drops them into the bottle.  



Immediately after the lit matches are dropped into the bottle, a peeled hard-boiled egg is placed on top of the mouth of the bottle.  The egg is quickly sucked into the bottle.



The demonstrator explains that the lit matches placed in the bottle heated the air within the bottle and the air expanded.  When the egg was placed on top of the bottle, a seal was created between the egg and the bottle, which cut additional oxygen off from entering into the bottle.  The lit matches inside of the bottle were quickly extinguished as the oxygen was used up.  This allowed the air inside of the bottle to rapidly cool and contract.  The contracting air within the bottle caused the egg to be sucked in.  The demonstrator explains that as the air contracts within the bottle, lower air pressure is artificially created inside of the bottle relative to the air outside of the bottle, and this is what causes the egg to be drawn in.  Beyond this, the demonstrator can underscore that differences between high and low air pressure cause the movement of air, which correlates to the wind we feel.  

Note:  A seven inch tall glass cappuccino bottle, or something similar, allows the experiment to work best.  Glass bottles with large inner volumes will severely restrict the expansion of air within the bottle unless 10 or more matches are used to heat the air in the bottle.  Of course, lighting this many matches at once may yield results you don’t want.  Additionally, the mouth of the bottle used must only be somewhat smaller than the circumference of the peeled hard-boiled egg.  If a bottle with too small of a mouth is used, the egg will either shear apart as it is pulled into the bottle or it will simply become lodged into the neck of the bottle and progress no further.  Never use plastic bottles for this experiment.   

Creating dew and frost 

This experiment works best when set up well in advance.  To set up the experiment, two thermometers are placed individually into two small metal bowls, which are then filled with ice and some water.  Rock salt is placed into one of the bowls.  Dew will form on the bowl that contains only ice and water.  If the experiment goes perfectly, frost will form on the bowl that contains ice, water and rock salt.  



The demonstrator directs the students’ attention to the two thermometers in the two bowls, which should show noticeable differences in temperatures.



 
The students are told rock salt has been added; to the bowl with the thermometer that is recording the colder temperature. It is explained that the rock salt absorbs latent heat from its surroundings, which causes a lower temperature in the bowl, and ideally, the formation of frost on the outside of the bowl.  The demonstrator then explains the formation of frost is an indication that water (dew) on the outside of the bowl has undergone a change of phase from a liquid to a solid.  Attendees are then asked where the water came from originally.  The correct answer is that it existed in the air as water vapor, which then appeared on the side of the bowl as a liquid after another change of phase brought about by the condensation process.
Inverted water-holding cup
 
In this experiment, a volunteer is solicited to hold a plastic drinking cup that is three-quarters full of water.  The demonstrator wets the rim of the cup and then places an index card on the rim of the cup.  The demonstrator then asks the volunteer to place the palm of the hand they are not using flat on top of the index card. 



Once this is done, the volunteer is asked to invert the cup and the index card, while they continue to hold both of them. After inverting the cup, the volunteer is asked to slowly remove their hand from underneath the cup. If the experiment works correctly, the index card will remain sealed against the rim of the inverted cup and no water, or very little water, will leak out.

 
This experiment is conducted to demonstrate, once again, the effect of air pressure. It is explained that because the pressure on the index card from the air outside of the cup is greater than the pressure of the water pushing down on the index card from inside of the cup, the water stays inside the glass. 

Coke and Mentos   Only conduct this experiment outdoors! 

This was the biggest attention-getter with regard to any of the experiments in the program.  It is designed to demonstrate one more aspect of air pressure.  Some preparation beforehand is also necessary for this experiment to be conducted properly.  To begin with, drill a 3/16th inch wide hole into a discarded plastic cap from either a 20 oz. or 2-liter plastic carbonated beverage bottle.  Drill a 1/8th inch wide hole into three pieces of Mentos candy.  String the three pieces of candy onto a paper clip, or a short firm wire, which has been bent into a “J” or fishhook shape. 

The demonstrator begins by having attendees recount what they have learned about high and low pressure.  The egg sucked into a bottle and the inverted water cup showed how high pressure outside of a container caused air to want to flow into the container where lower pressure existed.  In this experiment, the reverse would be shown, where a substance under high pressure inside of a container would want to flow to lower pressure outside of it.  Attendees are reminded what happens when a canned or bottled carbonated beverage is shaken and then opened.  It is explained that the demonstrator will attempt to super-charge the liquid inside of a 2-liter plastic carbonated beverage bottle to get more of the contents to come out of the bottle than otherwise would if the bottle was only shaken.

To conduct the experiment, the cap is taken off of a full 2-liter plastic carbonated beverage bottle.  The upper end of the “J”-shaped paperclip, or firm wire, is inserted into the hole of the previously drilled plastic cap from below.  The demonstrator then pinches and holds the end of the paperclip that is sticking up out of the hole in the cap.  The string of Mentos on the paperclip is then slid into the mouth of the full 2-liter bottle of carbonated beverage, which is standing on a solid level surface.  

   
The cap is screwed down tight on the bottle, while the paperclip is still being held.  After a brief countdown, “five, four, three, two…” the paperclip is released and the Mentos fall into the beverage.  A dramatic fountain of the carbonated beverage is then spewed upwards of 20 feet into the air.  (Fig. 11 and Fig. 12)  (Note:  The height of the fountain is dependent on the size of the hole drilled into the plastic cap, which has been screwed onto the 2-liter bottle.  For a taller fountain, drill a smaller hole.  For a wider, shorter fountain, bypass the placement of the plastic cap onto the 2-liter bottle entirely.  Additionally, it is recommended that a diet beverage be used to avoid sticky messes.  
 



Basic concept discussion:  When carbonated beverages are produced, they are bottled with carbon dioxide gas that is pushed into the bottle at a pressure about three times that of normal air.  The heavy pressure helps thousands of tiny carbon dioxide bubbles to dissolve into the beverage, but the high pressure also keeps them very small.  When the bottle is opened and the pressure is released, these bubbles get a little larger, and as they escape to the surface, they provide the characteristic fizz or carbonation.  These bubbles would get much bigger much quicker if not for the fact that the water molecules in the beverage attract strongly to one another.  The attractive force between water molecules, or surface tension, forms a tight web around each bubble and this makes it difficult for the bubble to expand.

When Mentos are added to a carbonated beverage, the candy begins to dissolve and the gelatin and gum arabic found in the candy instantly act to break up the surface tension between the water molecules.  This makes it easier for the bubbles to grow and thousands of tiny bubbles can instantly expand to hundreds of times their original size. Additionally, the rough surface of the Mentos provides many little nooks and cracks that help new bubbles to form.  The combination of these two processes causes the carbonated gas to erupt from the bottle like a super-heated geyser.   

For more information on this experiment, including several videos, please see the following web sites:

KSL TV Weather Experiments

NPR - All Things Considered 

Tornado in a bottle  The tornado in a bottle is constructed with two empty 2-liter plastic beverage bottles and a plastic coupling, which allows the 2-liter bottles to be screwed into it from each end.  This coupling can usually be purchased at a grocery store for $1 or $2.  Before connecting the two 2-liter bottles to the coupling, fill one of the bottles three-quarters full of water.  Also, add a couple of drops of dish soap and a couple of drops of food coloring to the water to help the vortex that will be made inside of the bottle to be more visible.(Notes:  As a caution, using yellow food coloring will typically garner giggles and funny remarks from youngsters for reasons that do not need to be explained here.  A poor-man’s version of this apparatus can also be constructed by using duct tape to hold the two 2-liter plastic bottles together.)   



  

Especially with younger kids, the demonstrator can begin this section of the program by asking if anyone knows what a meteorologist does.  In particular, it can be explained that a National Weather Service meteorologist is responsible for issuing warnings for severe weather.  From there, the demonstrator asks how people receive information about severe weather.  Attendees are then asked if they have ever seen a tornado.  Subsequently, they are asked if they know what to do if they see a tornado for themselves or are alerted to one in their area.  This is a great time to impart tornado safety messages.  After this explanation, the 2-liter bottle that contains water inside of it is held horizontally with two hands and rotated in circles to get the water inside of the bottle to swirl in one direction.  Once the water is in motion, the apparatus is tilted into the vertical and a tornado will form in the bottle. The particulars relative to the formation of actual tornadoes can then be shared with the attendees based upon the educational level of the attendees.



Written by Jim Reynolds
Webpage Composition by Steve Carmel and Michael Montefusco




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