## Monday, February 9, 2015

### Great Weather Experiments

Air Pressure - Two Simple Experiments     More than two hundred years ago, scientists discovered that a fluid (or material that flows) has lowest pressure wherever it moves fastest, and that air under high pressure (or air of greater density) flows towards areas of lower pressure (or where air is less dense). This can be demonstrated by conducting two simple experiments:
"1) Hold a strip of paper in front of your lips, with the strip hanging downward. Now blow over the top of the strip. The paper will rise because the pressure is greatest underneath the paper than above it. Since the pressure under the paper is not changed in any way, the moving air must have caused a lower pressure on the top of the paper.
"2) Place a piece of paper or card across two books of equal thickness separated by a small distance. Try blowing the paper or card off the books. You'll find it difficult to do so. The reason is that when you blow under the paper or card, between the books, the fast moving air causes a reduced pressure. The higher pressure above the paper or card then pushes down and makes it cling to the books. On the other hand, when you blow down on the paper or card the air also pushes the paper or card against the books. Thus, whether you blow over or under the paper or card it tends to cling to the books." (Quoted from an earlier non-referenced scientific publication.)
Here are some additional experiments on air pressure (taken from an earlier non-referenced scientific publication):

Air Pressure - The AirZooka Air Gun     The AirZooka air gun fires a 60-mph ball of wind up to 20 feet away. It uses several principles of physics--including those related to how air pressure changes as air travels faster and how atmospheric vortexes form.

"When you fire an AirZooka, a high-pressure shock wave leaves the toy first, quickly followed by an air ball. The shock wave creates a vortex of swirling air in its wake, which keeps the air ball intact and in place. If you've pulled the plastic sheet back just right, the ball threads the spinning ring of air and carries it on to your target. If your shooting angle is a bit off, however, you shoot a ring of air, not an air ball--though it feels the same to your target." (Discover magazine, June 2003). As of September 2003, the AirZooka air gun sold for about \$11.00.

Clouds - Make a Cloud in a Cloud-Forming Apparatus     "A cloud forming apparatus consists of a glass bulb having two tube outlets. One of these is attached to a rubber bulb, the other to a rubber tube having a pinch clamp. The rubber blub is partially filled with water. The air in the glass bulb becomes nearly saturated with water vapor because it is standing over the water surface located in the rubber bulb. Smoke is introduced into the glass tube through the rubber tubing and the clamp is then closed. The rubber bulb is compressed, then suddenly released, causing the air in the glass bulb to expand and cool, and water vapor to condense around the smoke particles that results in a 'cloud' of visible water droplets forming in the glass bulb." (Quoted from a non-referenced scientific instrument publication.)
As of September 2003, a Cloud-Forming Apparatus is available from Wards Natural Science for \$36.75. Wards states the following about its Cloud-Forming Apparatus: "Show fog and cloud conditions over and over again with this simple device, water, and the introduction of dust or smoke particles. Water and dust are regulated by simply squeezing the attached rubber bulb. The model consists of a glass flask with a rubber bulb and rubber tube with pinch clamp. Height: 11"; volume: 500 mL."

Tornadoes - Tornado Demonstration      "The 'pressure' of air is the 'weight of air' on an object. Under 'high pressure,' air molecules press down on an object and pack close together. Under 'low pressure,' air molecules rise and spread apart. Air flows from an area of high pressure to an area of low pressure. The flow of air is called 'wind.'
"Nearly 250 years ago, scientists discovered that the faster air travels the lower its pressure. Therefore, when a tornado--which has extremely low pressure and fast winds of 100 to over 300 mph--approaches an object, the object is literally 'pushed' towards the tornado by the 'higher' pressure air outside the tornado that is trying to move into the tornado.
"You can demonstrate the above facts by using a simple vacuum tube and pieces of packing foam. By spinning the top of the tube with one hand, you'll create 'low' air pressure in the tube. The 'higher' air pressure in the room will move towards the bottom of the tube and push the pieces of packing foam off the table and up into the tube. This is exactly what happens when a tornado approaches an object--like a car or house." (Quoted from non-referenced scientific teaching materials.)
Note: According to the AMS Bulletin of April 1988: "Opening windows during tornadoes does not protect your home and it could cost your life.... The time spent in opening windows does little to save your home and should be devoted to seeking shelter because of the danger of flying glass.... For years it was thought that a home could be protected against a tornado's sudden drop in atmospheric pressure by opening windows. It is now known that the practice increases the chances of collapse by exerting higher pressure on the wall opposite from the open window.... Studies reveal that most buildings have adequate venting, which allows for sudden pressure drops."

Above: Clayton Brough uses white packing foam and a spinning vacuum hose to demonstrate that "By spinning the top of the tube with one hand, you'll create 'low' air pressure in the tube. The 'higher' air pressure in the room will move towards the bottom of the tube and push the pieces of packing foam off the table and up into the tube. This is exactly what happens when a tornado approaches an object--like a car or house."