Materials Included In Kit

Additional Materials Required

Prelab Preparation

Activity C. Relative Humidity and Dew Point

1. Construct a wet-bulb thermometer by slipping a small piece of cotton wick over the bulb of one of the thermometers. The other thermometer is the dry-bulb thermometer.
2. Attach the two plastic-backed thermometers together back-to-back using a small rubber band (see Figure 2).
   {12712_Preparation_Figure_2}
3. Slide both of the thermometers onto the screw through the hole used to hang the thermometers.
4. Twist the screw carefully into the end of the plastic handle (with the predrilled hole in it) until 3 or 4 mm of the screw’s shaft remains above the handle.
5. Place the rubber cap on the bottom end of the psychrometer handle.

Activity E. PolySnow™

Before class, add approximately 3.0 g of PolySnow to each plastic cup or set up balances at each Activity E Station.

Safety Precautions

Do not use glass bottles with the Tornado Tube. Be sure that the thermometers are securely attached to the plastic handle before swinging. Inspect the assembled sling psychrometer prior to student use. Be careful not to drop or break the thermometers. Wear protective eyeware. Use extreme care when using matches for the Cloud in the Hand Activity. PolySnow is nontoxic. However, it is irritating to the eyes and to the nasal membranes if inhaled. Wear chemical splash goggles whenever working with chemicals, heat or glassware. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The plastic bottles may be recycled. The rest may be placed in the trash according to Flinn Suggested Disposal Method #26a.

Teacher Tips

• Activity A. Tornado Tube

• You may wish to add food coloring or glitter to the water to create special effects.
• Allow students to experiment with the Tornado Tube assembly. See if they can figure out the best and fastest way to get the liquid from the top bottle to the bottom bottle. Many will discover that the most efficient technique is to create a vortex, which is a swirling motion in the fluid.
• Compare the fluid transfer rate with and without a vortex in the Tornado Tube. To do this, time how long it takes for the liquid to fall when the assembly is inverted and simply set on the table (like a sand timer). Then repeat, but this time swirl the assembly to create the tornado action.

  Activity B. Pet Tornado and Fujita Scale

• The Pet Tornado should be shaken in a circular motion and held exactly straight up and down for the best effect. The Pet Tornado may also be shaken in a circular motion and placed on the tabletop.

  Activity C. Relative Humidity and Dew Point

• One foot of cotton wick is included. Cut the cotton wick into ½" pieces for use. Extra wick is included as a surplus supply.
• Relative humidity and dew point values are given for temperature ranges between 32 and 94 degrees Fahrenheit. Plan this activity accordingly.
• The sling psychrometer may be assembled ahead of time by the instructor or in class by the students. Be sure to inspect the psychrometer before each use.

  Activity D. A Cloud in the Hand

• Consider introducing several different types of clouds. The following table describes 10 types of clouds and at what altitude they typically form.
  {12712_Tips_Table_3}
• Repeat the demonstration, only this time do not use the smoke from the match. No cloud will form. This will reinforce the concept that particles in the air are required for cloud formation.
• More precise examples and explanations of clouds can be found on the Skywatcher’s Cloud Chart (Flinn Catalog No. AP5301.)
• Flinn Scientific also carries a glass cloud-forming demonstration model called the Ultimate Cloud Forming Apparatus, AP5302.

Further Extensions

Activity A. Tornado Tube

• The Liquid Race: Have three or four tornado tubes connected to pairs of two-liter bottles. Select several students to demonstrate the best method of transferring the liquid from one bottle to the other. Give them a limit of 10 seconds. Be sure to point out that they may only handle the bottle for 10 seconds. At the end of that time, wait one minute to make sure all the liquid that is going to fall from the top bottle has fallen into the bottom bottle. Measure the volume of liquid in each bottle. Then demonstrate how you would transfer the liquid. The best and fastest way is to create a vortex by swirling the bottles. If you like, you can challenge them to transfer more liquid than you can in 10 seconds. The best they will ever be able to do is tie.
• The Tornado Tube Density Bottle: Make a density bottle using a one-liter bottle to which you add about 500 mL of corn oil and 500 mL of colored water. Connect this to a second one-liter bottle with a Tornado Tube and invert. Swirl the liquid to transfer the liquid from the top to the bottom. If you do not swirl too hard, all of the water will fall through the hole (since water is more dense than oil), vortex action will stop, and the liquid will stop transferring. This may be explained in terms of attractive forces between molecules. Since the water molecules are polar and the corn oil molecules are nonpolar, they have little influence on each other. The vortex is the result of the attraction of water molecules to each other and, once set in motion, they pull other water molecules along. This pull is not transferred to the corn oil. When the interface is reached between the two liquids, the transfer stops.

Activity B. Pet Tornado and Fujita Scale

• Have students further research the devastation caused by the different F or EF levels of tornadoes.

Activity C. Relative Humidity and Dew Point

• This activity may be done over an extended period of time to see the long-term relative humidity and dew point trends.
• Have students compare their calculated values to values given by a local weather station or the National Weather Service.

Activity E. PolySnow™

• Make a batch of PolySnow and freeze it. If you live in a climate where it snows, compare the frozen PolySnow to real snow. Could PolySnow be used in place of manmade snow on ski slopes?
• Place 3 g of PolySnow into a 1000-mL graduated cylinder. Add 150 mL of deionized water and measure the amount of swelling that occurs. Conduct experiments to determine the following:
  • How does the swelling rate change with different amounts of polymer?
  • How does the swelling rate change with different amounts of deionized water?
  • How does the rate of swelling change when PolySnow is dissolved in hot deionized water versus cold deionized water?
  • Does deionized water produce greater swelling than tap water?
  • Determine conditions to achieve the greatest amount of swelling.
• Use food coloring to color the water before adding it to the PolySnow. Fill a graduated cylinder with layers of colored “snow.” Let the snow layers sit undisturbed to see if any color mixing occurs

Answers to Questions

Activity A. Tornado Tube

1. Describe the motion of the water as it enters the lower bottle.

   The small rotation of the bottles creates a vortex in the bottle.

2. What is causing the vortex to form?

   The vortex forms a type of valve through which the displaced air can escape quickly as the rotating liquid falls through the opening. Gravity is the force that pulls the liquid into the hole, forming a continuous vortex.

3. How does the formation of the vortex compare to how tornadoes occur?

   In the atmosphere, the kinetic energy in a tornado vortex arises from varying air temperatures and strong winds. A tornado usually forms during a severe thunderstorm when a cold front meets a warm front. Cold air is forced downward as warm air is forced upward at great speed, causing very low pressure at the Earth’s surface. Strong winds approaching the center of the low-pressure system collide from different directions and begin to rotate violently. When this happens, the air pressure inside drops rapidly and a funnel cloud, or tornado, appears.

4. Repeat the procedure once again without swirling the bottles. Compare the results with the original procedure.

   The water evacuates the upper bottle at a much slower rate when a vortex is not formed.

Activity B. Pet Tornado and Fujita Scale

1. Describe what occurs when the Pet Tornado is shaken.

   A very rapidily moving vortex, or mini-tornado, forms when the Pet Tornado is shaken in a circular motion.

2. Once Activities A and B have been completed, compare and contrast the vortexes formed in each device.

   The vortex formed in this activity (Activity B) has much more of a winding motion than the vortex in Activity A. It is also much more short-lived. The vortex in Activity A is much more vertical and lasts longer than the one in Activity B.

3. Describe the Fujita Scale.

   The Fujita scale is a scale for rating tornado intensity based on damage tornadoes caused to human-built structures and vegetation. This scale ranks the increasing intensity of tornados from F0 to F6.

4. How does the Enhanced Fujita Scale (EF) differ from the Fujita Scale?

   The EF scale accounts for degrees of damage that occurs to an extensive list of structures, both manmade and natural. The expanded and refined damage indicators provide a better estimate for overall wind speeds.

Activity C. Relative Humidity and Dew Point

1. Define the terms relative humidity and dew point.

   Relative humidity is the percentage of moisture air is holding compared to the maximum it can hold. Dew point is defined as the temperature at which air must be cooled (at constant pressure and water vapor content) for saturation (dew formation) to occur.

2. Given your results, how do relative humidity and dew point compare?

   Answers will vary. When the air temperature and dew point are dramatically different, the relative humidity is low. When the air temperature and dew point are close to the same value, the relative humidity is high. When the air temperature and dew point are the same, the relative humidity is 100%.

3. Compare your relative humidity and dew point values with your local weather station or Internet weather site. How do your values compare to the actual or reported values?

   Answers will vary.

Activity D. A Cloud in the Hand

1. What does the smoke from the match represent?

   The smoke from the match represents particles in the atmosphere.

2. What causes the cloud to form in the bottle?

   Squeezing the bottle dramatically increases the pressure (and slightly increases the temperature) inside the bottle. At this higher pressure some of the water that was in the vapor phase returns to the liquid phase until a new equilibrium state is reached. When the pressure on the bottle is released the pressure (and temperature) within the bottle drops suddenly, creating a partial vacuum. To reattain equilibrium, water now goes from the liquid phase to the vapor phase. At this point the area above the liquid becomes saturated with water vapor which condenses on the “airborne” smoke particles (condensation nuclei) to form the cloud. This saturation is caused by unequal pressures of the liquid and vapor phases upon expansion of the bottle.

3. What would happen if the smoke from the match was not present? Why?

   If the smoke from the match was not present, the cloud would not form within the bottle.

Activity E. PolySnow™

1. Explain why the artificial “snow” forms when the water is added to the PolySnow power.

   The PolySnow absorbs the water because the osmotic pressure of the PolySnow forces water into the solid polymer lattice in an attempt to equilibrate sodium ion concentration inside and outside the polymer membrane.

2. Compare and contrast PolySnow to real snow.

   Student answers will vary.

3. What happens when salt is added to the PolySnow? Give an example of how this process is commonly used.

   When salt is added to the PolySnow, a slurry is formed. This is similar to the process of placing salt on the roads to melt the snow during winter.

Teacher Handouts

12712_Teacher1.pdf

Introduction

Weather is all around us! Perform the following weather-related activity stations to gain a better understanding of common weather events.

Concepts

• Tornadoes
• Dew point
• Snow
• Relative humidity
• Cloud formation
• Air pressure
• Kinetic energy
• Fluid motion
• Vortex action
• Fujita scale
• Water vapor
• Condensation
• Gas laws
• Polymers
• Osmosis
• Super absorbent
• Cross-linking

Background

Activity A. Tornado Tube
The purpose of the Tornado Tube is to cause the water in the top bottle to empty into the lower bottle as quickly as possible. The lower bottle, however, is not empty—it is filled with air. Air takes up space, so in order for the water to flow from the upper bottle into the lower bottle, the air has to be displaced to the upper bottle. The way to do this is to create a vortex in the water. A vortex is a tornado-like, swirling motion that causes a liquid or a gas to travel in a spiral around a center line. Because the center of a vortex is hollow, the air from the lower bottle flows through the vortex into the upper bottle as the water flows downward into the lower bottle.

This interesting phenomenon of vortex action can also be observed in everyday occurrences. Examples include the way water swirls as it drains when the plug is pulled in a bathtub drain, and miniature rotating tornadoes called dust devils are produced by gusty winds. Then there is the most commonly known example—a fierce windstorm or powerful rotating column of air known as a tornado.

Vortex action results from a concentration of kinetic energy, or motion, within a fluid. In the atmosphere, the kinetic energy in a tornado vortex arises from varying air temperatures and strong winds. A tornado usually forms during a severe thunderstorm when a cold front meets a warm front. Cold air is forced downward as warm air is forced upward at great speed, causing very low pressure at the Earth’s surface. Strong winds approaching the center of the low-pressure system collide from different directions and begin to rotate violently. When this happens, the air pressure inside the vortex drops rapidly and a funnel cloud, or tornado, appears.

With the Tornado Tube, the initial slow rotation of the bottles creates a similar-type vortex. The vortex forms a type of valve from which the displaced air can quickly escape as the rotating liquid falls through the opening. The force of gravity pulls the liquid into the hole, forming a continuous vortex, that will naturally spin until something occurs to stop it.

Activity B. Pet Tornado and the Fujita Scale
The Fujita scale is a scale for rating tornado intensity based on damage caused by the tornadoes on human-built structures and vegetation. When a tornado occurs, the official Fujita scale rating is determined by meteorologists after a ground or aerial damage survey. Eyewitness and media reports are also considered when determining the Fujita scale rating. The Fujita scale, which was introduced in 1971 by Dr. T. Theodore Fujita, is broken down into 6 categories as shown in Table 1.

Some of the original wind speed numbers have since been found to be higher than the actual wind speeds required to cause the damage described in each category. The wind speed numbers were found to be increasingly inaccurate as the F# category increases. Therefore another scale called the Enhanced Fujita (EF) scale was created and, as of early 2007, it is now considered to be the standard for rating tornadoes. The EF scale accounts for degrees of damage that occurs to an extensive list of structures, both man-made and natural. The expanded and refined damage indicators provide a better estimate for wind speeds and set no upper limit for the wind speeds of the strongest level tornados, EF5. The wind speeds are defined at a three-second gust (mph) in the EF scale. See the refined EF scale in Table 2. The back of the Pet Tornado model lists the types of damage that typically result from each type of tornado. Activity C. Relative Humidity and Dew Point
Water vapor is the gaseous, invisible form of water in the atmosphere. It is better known as humidity. When the air in the atmosphere contains a large amount of water, the air feels very humid. The opposite is true when the air is relatively void of water vapor—the air feels very dry. When air holds the maximum amount of moisture, dew or frost will be present and small droplets will begin to form as clouds. As the clouds become saturated with water droplets, they will become too dense to hold all of the droplets and the droplets will start to fall toward the Earth’s surface in the form of rain or snow. This is known as 100% humidity.

A sling psychrometer can be used to measure the relative humidity of the air. Relative humidity is the percentage of moisture air is holding compared to the maximum it can hold. When water in the air evaporates, a certain amount of heat is required to convert the air into water vapor. Therefore, a cooling effect takes place when evaporation occurs. A sling psychrometer consists of two thermometers; a dry-bulb and a wet-bulb. The dry-bulb thermometer measures the temperature of the surrounding air while the wet-bulb thermometer records the amount of cooling that is required for the water to evaporate at that specific temperature. If the air is very humid, the differences between the dry-bulb and wet-bulb thermometers will not be large because there is little evaporation. However, if the air is arid or dry, a large amount of evaporation takes place (which causes a cooling effect on the wetbulb thermometer) and the difference between the two temperatures of the thermometers will be greater.

To use the Relative Humidity Table, first find the temperature difference between the dry- and wet-bulb thermometers. Locate this value on the Relative Humidity Table. Now use this value and the final temperature of the dry-bulb thermometer to obtain the relative humidity reading.

Dew point is defined as the temperature at which air must be cooled (at constant pressure and water vapor content) for saturation (dew formation) to occur. When the dew point is below freezing, (32 °F), it is commonly referred to as the frost point.

The dew point is an important measurement used to predict the formation of dew, frost and fog. Since atmospheric pressure varies only slightly at the Earth’s surface, the dew point is a good indicator of the air’s water vapor content. High dew points indicate high water vapor content and low dew points indicate low water vapor content.

The difference between the air temperature and dew-point temperature indicates whether the relative humidity is low or high. When the air temperature and dew point are dramatically different, the relative humidity is low. When the air temperature and dew point are close to the same value, the relative humidity is high. When the air temperature and dew point are equal, the relative humidity is 100% (see the Dew Point Calculation Chart in the Teacher PDF).

To find the dew point, use the temperature of the air and the relative humidity percent reading. Find each of these values on the Dew Point Calculation Chart and locate the corresponding dew point value.

Activity D. A Cloud in the Hand
This activity provides a rough analogy for cloud formation in the atmosphere. Water is added to a 1-liter plastic bottle along with smoke from a burning match and then capped. Squeezing the bottle dramatically increases the pressure (and slightly increases the temperature) inside the bottle. At this higher pressure some of the water that was in the vapor phase returns to the liquid phase until a new equilibrium state is reached. When the pressure on the bottle is released the pressure (and temperature) within the bottle drops suddenly, creating a partial vacuum. To re-attain equilibrium, water now goes from the liquid phase to the vapor phase. At this point the area above the liquid becomes saturated with water vapor which condenses on the “airborne” smoke particles (condensation nuclei) to form a cloud. This saturation is caused by unequal pressures of the liquid and vapor phases upon expansion of the bottle. Think of the inequality of pressure as an instantaneous partial vacuum.

After going through a few squeeze and release cycles hold the bottle up to a fluorescent (overhead) light. By releasing and applying the pressure slowly, various colors may be evident (primarily purple and orange). This occurs because light passing through the bottle is differentially scattered by the smoke particles as the pressure varies, similar to the atmospheric effects seen at sunset!

Activity E. PolySnow™
Snow is a type of precipitation in the form of crystalline ice consisting of numerous snowflakes that fall from clouds. Snow is composed of small ice particles and is a granular material. It has an open and soft structure, unless packed by external pressure.

Snow forms when water vapor condenses directly into ice crystals, usually in a cloud. These crystals typically have a diameter of several millimeters and have six lines of symmetry. A snowflake is an aggregate of these ice crystals and may be several centimeters large. The individual ice crystals are clear, but because of the amount of light reflected by the numerous individual crystals, snowflakes usually appear white in color unless contaminated by impurities.

In this activity, an artificial snow made of a chemical known as PolySnow will be studied. PolySnow is an example of a super absorbent polymer. Superabsorbents operate on the principle of osmosis—the passage of water through a membrane permeable only to water. In PolySnow, osmotic pressure results from a much greater concentration of sodium ion inside of the polymer lattice membrane than in the solution in which it is immersed. This osmotic pressure forces water into the solid polymer lattice in an attempt to equilibrate sodium ion concentration inside and outside the polymer membrane. The electrolyte concentration of the water will affect the osmotic pressure, subsequently affecting the amount of water absorbed by the polymer. For example, PolySnow will absorb approximately 500–800 times its own weight in distilled water, but will only absorb about 300 times its own weight in tap water, due to the high ion concentration of tap water.

Experiment Overview

The purpose of this “activity-stations” lab is to investigate and explore the following weather events—tornadoes, relative humidity, dew point, cloud formation and snow. There are five activity stations set up around the lab. Each one focuses on a weather event and is a self-contained unit, complete with background information and discussion questions. The activities may be completed in any order.

• Activity A. Tornado Tube
• Activity B. Pet Tornado and Fujita Scale
• Activity C. Relative Humidity and Dew Point
• Activity D. A Cloud in the Hand
• Activity E. Polysnow™

Materials

Safety Precautions

Do not use glass bottles with the Tornado Tube for safety reasons. Be sure that the thermometers are securely attached to the plastic handle of the sling psychrometer before swinging. Inspect the assembled sling psychrometer prior to use. Wear protective eyewear in the lab. Be careful not to drop or break the thermometers. Use extreme care when using matches for the Cloud in the Hand Activity. Although PolySnow™ is nontoxic, it is irritating to the eyes and to the nasal membranes. Wear chemical splash goggles whenever working with chemicals, heat or glassware. Please review current Safety Data Sheets for additional safety, handling and disposal information. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Activity A. Tornado Tube

1. Fill one plastic soda bottle approximately two-thirds full with water.
2. Screw the Tornado Tube onto this bottle.
3. Attach the other empty plastic soda bottle to the other end of the Tornado Tube.
4. Invert the assembly so that the water-filled bottle is on top.
5. Holding the assembly securely, swirl the bottles briefly in a small circular motion to create tornado action, or a vortex. (Note: The direction of rotation may be either clockwise or counterclockwise.) Observe the resulting fluid motion.
6. Answer the questions in Observations and Results.

Activity B. Pet Tornado and the Fujita Scale

1. Shake the Pet Tornado vigorously.
2. Let the bottle settle until the viewing area is clear.
3. Hold the bottle upright and shake briskly a few times in a circular motion (see Figure 1).
   {12712_Procedure_Figure_1}
4. Observe what happens in the viewing area.
5. Repeat steps 1–4 as desired.
6. Answer the questions in Observations and Results.

Activity C. Relative Humidity and Dew Point

1. Determine the air temperature using the dry-bulb thermometer. Record the temperature in the data table.
2. Using a Beral-type pipet, place a few drops of water on the cotton wick of the wet-bulb thermometer.
3. Place the plastic handle of the sling psychrometer in your hand and slowly rotate the thermometers around the screw. The spinning motion will increase the rate of the evaporation rate of the water.
4. Spin the thermometers on the sling psychrometer for thirty seconds or until the wet-bulb thermometer drops to a point where it remains constant.
5. When the wet-bulb thermometer reading is stable, immediately record the temperature of both thermometers in the data table.
6. Determine the difference between the dry-bulb and wet-bulb thermometers. Record this value in the data table.
7. Use the Relative Humidity Table (in the Teacher PDF) to determine the relative humidity of the air. Record this value in the data table.
8. Use the relative humidity value and the Dew Point Calculation Chart to determine the dew point. Record this value in the data table.
9. Answer the remaining questions in the Observations and Results section.

Activity D. A Cloud in the Hand

1. Add approximately 10 mL of water (room temperature) to the 1-L bottle and screw on the cap.
2. Shake the bottle to distribute the water on the interior surface and let the bottle stand for at least a few minutes. This will allow time for some of the water to evaporate.
3. Uncap the bottle and light a match. Allow the match to burn for a few moments. Extinguish the match and immediately toss it into the bottle. Quickly cap the bottle very tightly, trapping some of the smoke from the extinguished match.
4. Using both hands, squeeze the bottle. The pressure in the bottle will increase significantly.
5. Quickly release your grip and observe the bottle interior. A cloud will form. Repeat as often as desired.
6. Answer the questions in Observations and Results.

Activity E. PolySnow™

1. Add 3 g of Polysnow to a plastic cup.
2. Add approximately 150 mL of distilled or deionized water to another plastic cup.
3. Slowly add the water to the cup containing the 3 g of PolySnow. The PolySnow will turn white and start to grow. Within a minute, it will overflow the cup.
4. Add a small amount (1 g) of sodium chloride to the cup of PolySnow. The PolySnow will release the water and transform it to a slurry.
5. Answer the questions in Observations and Results.

Student Worksheet PDF

12712_Student1.pdf