Effects of High and Low Pressure (Catherine Eskandar)

Title: Effects of High and Low Pressure

Principles Investigated: High Pressure, Low Pressure, and Condensation.

Standards:

Grade 5 Earth Science

3.C Students know water vapor in the air moves from one place to another and can form fog or clouds, which are tiny droplets of water or ice, and can fall to Earth as rain, hail, sleet, or snow.

Grade 6 Earth Science

Energy in the Earth System

4.E Students know differences in pressure, heat, air movement, and humidity result in changes of weather.

Materials:

Clear plastic bottle with cap (Large Kirkland water bottle or soda bottle)

Foot pump or bicycle pump with rubber stopper attached. (I didn’t have a rubber stopper so I used duct tape to hold the pump in place without letting air escape.)

Water

Rubbing alcohol

Safety glasses

Procedure:

· Place just a few drops of rubbing alcohol in the bottom of the bottle.

· Swirl the alcohol around in the bottle, making sure to coat the sides.

· Then put the rubber stopper in the bottle. (Or tape the pump to the bottle to hold in place.)

· Pump air into the bottle using the bicycle pump. (About 15-20 pumps for a more impressive cloud.)

· When you are done pumping, remove the stopper. (In my case, yank off the pump from the tape.)

In order to demonstrate the return of clear skies:

· With the cloud still formed in the bottle, attach the pump again and pump air into the bottle again until the bottle is clear.

· The bottle is now experiencing beautiful sunny weather. Clear skies…clear bottle!

Prior Knowledge:

Students must have a basic understanding of the water cycle. If working with the lower grades, the focus should be placed more on the basics of condensation. (Water vapor condenses and creates a cloud.)

For the upper grades, students should have an understanding of the water cycle and the different wind patterns around the planet. (Coriolis Effect, Hadley cell circulation, atmospheric pressure variations, etc.)

Explanation:

Cloud in a Bottle

Introduces the basic principles behind cloud formation and how it relates to high and low pressure. Shows how pressure and water vapor in the air compress and expand in a small scale version of what happens in the atmosphere every day. As you pump air into the bottle with the pump, you’re creating high pressure. Since high pressure areas are where we typically see clear skies, the bottle is free of any clouds. Once the stopper is removed, you are stimulating a cold front since the pressure of the air outside the bottle is much lower. The pressure inside the bottle is released and a condensation occurs forming a cloud.

The Liquid = Water Vapor

Even though we don't see them, water molecules are in the air all around us. These airborne water molecules are called water vapor. When the molecules are bouncing around in the atmosphere, they don't normally stick together. Pumping the bottle forces the molecules to squeeze together or compress. Releasing the pressure allows the air to expand, and in doing so, the temperature of the air becomes cooler. This cooling process allows the molecules to stick together - or condense - more easily, forming tiny droplets.

Why Use Rubbing Alcohol?

The reason the rubbing alcohol forms a more visible cloud is because alcohol evaporates more quickly than water. Alcohol molecules have weaker bonds than water molecules, so they let go of each other more easily. Since there are more evaporated alcohol molecules in the bottle, there are also more molecules able to condense. This is why you can see the alcohol cloud more clearly than the water cloud.

High Pressure - A region where the atmospheric pressure at the surface of the planet is greater than its surrounding area. On a weather map, high pressure areas are generally associated with fair, sunny weather. As high pressure is an area of sinking air, and air tends to dry out as it sinks, leaving sunny CLEAR skies.

Low Pressure - A region where atmospheric pressure at sea level is below that of surrounding location. Low pressure areas are generally cloudy/rainy areas; where we have the stormiest weather. Low pressure areas are of rising air, and as air rises, it condenses into clouds and rain. Air moves from higher pressure to lower pressure, so if you have a high and a low nearby, it can be windy as air rushes between the two. The stronger the pressure difference, between the nearby high pressure system and low pressure system, the stronger the wind. Thus, stronger areas of low pressure are associated with stronger winds.

Unit of Pressure - Pascals (Pa) are the SI unit of pressure. A unit of force per unit area. (One newton per square meter.) In weather reports, it is used in the form of hectopascals or kilopascals. (1hPa = 100Pa 1kPa = 1000 Pa) Named after the French mathematician, physicist, inventor, writer and Catholic philosopher Blaise Pascal.

1 pascal (Pa) = 1 N/m² = 1 kg/(m·s²)

Q&A

1. How can you prevent condensation in your car?

- We turn up the heat to prevent condensation so that our view isn’t obscured.

2. Where else do we see the rising and sinking of hot and cold substances?

- A teapot that contains boiling water. Hot water rises where as the cooler water sinks. The cool water soaks up more heat and the cycle repeats.

3. In a high pressure area, which way does the wind flow?

- Wind flows outward. This is because of the higher density of the air near the center.

Applications to Everyday Life:

· Butane and Propane Gas Tanks – these gases, when compressed and stored under high pressure in the tank form a liquid. When the tank is opened, you release the it into a gas form.

· Dry Ice - Through a process called sublimation, under the right amount of pressure, the ice which is a form of solid carbon dioxide, changes into a gas.

· Adding Air to Tires – If your tire pressure is low, never change your car’s tire pressure when it’s cold out. The molecules are contracted since it’s cold. When the temperature outside warms up, the molecules will expand and cause your tire to pop!

Applications of Condensation:

· When my glasses fog up upon entering a warm room on a cold day.

· When it’s warm out and you pour yourself a cold beverage. Water droplets start to form on the outside of your glass.

· After taking a hot shower, the mirrors in the bathroom create condensation and you can doodle with your finger.

References:

"Cloud in a Bottle at Steve Spangler Science." Science Projects Experiments, Educational Toys & Science Toys. Web. 05 Dec. 2010. <http://www.stevespanglerscience.com/content/experiment/00000030>.

"Introduction to Air Pressure (Part I)." Hong Kong Observatory-Official Authority For Hong Kong Weather Forecast. 03 Oct. 2009. Web. 05 Dec. 2010. <http://www.weather.gov.hk/education/edu01met/wxobs/ele_pressure1e.htm>.

"High-pressure Area." Wikipedia, the Free Encyclopedia. 03 Dec. 2010. Web. 05 Dec. 2010. <http://en.wikipedia.org/wiki/High-pressure_area>.

"Low-pressure Area." Wikipedia, the Free Encyclopedia. 27 Nov. 2010. Web. 05 Dec. 2010. <http://en.wikipedia.org/wiki/Low_pressure_area>.

Pool, By Steve. "How Do High Pressure and Low Pressure Affect Our Weather? | Seattle News, Weather, Sports, Breaking News | KOMO News | F.A.Q." Seattle News, Weather, Sports, Breaking News | KOMO News. Web. 05 Dec. 2010. <http://www.komonews.com/weather/faq/4347756.html>.

"YouTube - Cloud in a Bottle - Cool Science Experiment." YouTube - Broadcast Yourself. Web. 05 Dec. 2010. <http://www.youtube.com/watch?v=msSVQ903T8k&featu>.