Author: Maddie Van Beek

It's almost December and the weather will be getting colder! In Fargo, the roads and sidewalks can get pretty icy, so people take extra care with driving and walking in the winter. ​Have you ever seen salt on the sidewalks in the wintertime? Most of you probably know that salt causes ice to melt. People sprinkle salt on icy sidewalks to make them less slippery. Have you ever wondered how that works? That’s what we are going to find out today!

Why does salt melt ice?

When you dissolve salt in water, the water is harder to freeze. Usually, water freezes at 32 degrees Fahrenheit (0 degrees Celsius). When you add salt to water, it has to be colder than 32 degrees Fahrenheit in order to freeze. Thus, adding salt to water lowers the freezing temperature.
​
Watch this video to find out more about the science behind why salt melts ice: 
​

Check out this link for more information: 
http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm
 
Now that you know why salt melts ice, let’s test it out!
 
YOU WILL NEED:

• Clear glass
• Water
• Ice cubes
• String

 
Here’s what to do!

1. Fill your glass about ¾ full with water.
2. Add about 5 ice cubes.
3. Cut a piece of string about 1 foot long.
4. Dangle the string into the water and try to catch an ice cube. When you lift the string out, do any ice cubes stick to it?
5. Let’s try it again. Dangle the string into the water over the ice cubes. This time, sprinkle some salt over the ice cubes. Wait a few seconds, then lift the string up. Do any ice cubes stick this time? Yes! Why did the salt make the difference? Remember, salt causes ice to melt! When you sprinkled salt on the ice cubes, they began to melt, but the water around it quickly refroze. The refreezing trapped the string onto the surface of the ice cubes. See how many ice cubes you can catch at once!
6. Does more salt change the effect? Try it out!

 
Now that you know how salt affects ice, use this same science to make your own slushy without the aid of a freezer!
​
YOU WILL NEED:

• Fruit juice
• Ice cubes
• 1 Gallon Ziploc bag
• 1 smaller Ziploc bag
• Salt

 
Here’s what to do!

1. Carefully pour fruit juice into the smaller bag and seal it shut.
2. Put ice cubes into the gallon-sized bag and add the salt.
3. Place the sealed smaller bag inside the gallon-sized bag.
4. Seal the larger Ziploc bag shut.
5. Shake it up!!!
6. Remember, salt lowers the freezing temperature of ice, so it causes the ice to melt. As the ice melts, the salty mixture also becomes colder… just cold enough to freeze up your fruit juice!
7. Once your fruit juice reaches the desired slushy consistency, place the bag in the sink, remove the smaller bag from the larger one and rinse it off with cold water.
8. Open your fruit juice bag and enjoy your homemade slushy!

 
References
http://www.sciencekiddo.com/salt-melts-ice-experiment/
http://www.sciencekiddo.com/fruity-ice-slush/
https://www.highlightskids.com/science-questions/how-does-salt-melt-ice-and-snow
http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm
​https://en.wikipedia.org/wiki/Salt

Image and video credits, in order of appearance:

Soric, D., 2009. Salt shaker on a white background. Image uploaded from Wikimedia Commons on 11/27/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/7/78/Salt_shaker_on_white_background.jpg/800px-Salt_shaker_on_white_background.jpg File used in accordance with the 
Creative Commons Attribution 2.0 Generic Image was not changed. 

Chhe, 2009. SEM image of a grain of table salt. Image uploaded from Wikimedia Commons on 11/27/2016. https://upload.wikimedia.org/wikipedia/en/thumb/9/9b/Single_grain_of_table_salt_%28electron_micrograph%29.jpg/800px-Single_grain_of_table_salt_%28electron_micrograph%29.jpg File in the Public Domain. 

Heidas, 2005. Schneepflug strasse hinten. Image uploaded from Wikimedia Commons on 11/27/2016.
https://en.wikipedia.org/wiki/Winter_service_vehicle#/media/File:Schneepflug_Strasse_hinten.jpg File used in accordance with the CC Attribution-Share Alike 3.0 Unported. Image was not changed

Reactions, 2015. How does salt melt ice? Video uploaded from YouTube on 11/27/2016. https://youtu.be/JkhWV2uaHaA

Author: Maddie Van Beek

It has been a HUMID week in Fargo, North Dakota! What does humidity mean? Humidity is the amount of moisture that is in the air. When it's humid out, it makes a hot day feel even hotter. Have you ever gotten out of a hot shower and seen steam on your mirror? It sure feels muggy if you have the door closed without the fan running! Why is it that humid air makes it feel warmer?



Test it out:



1. Stand in your bathroom with the door closed. Bring a thermometer in and check the temperature.

2. Turn the shower on hot and leave the thermometer in the bathroom. Shut the door and leave the bathroom for about three minutes.

3. Come back and check it out. What do you notice about the mirror? Does the air feel different? Check the thermometer for any temperature changes.



You probably noticed that the bathroom felt much warmer after the hot shower had been running for a while!



Option 1: Analyze the weather



YOU WILL NEED:

• Internet to check weather. 
  

1. Check the weather each day for two weeks. Record the high, the low, the humidity, and the "feels like."

2. Analyze your results.

Questions to think about: 

* Was the humidity typically higher on hotter days or cooler days?

* Did the humidity affect the "feels like" temperature?

* Did the humidity have a larger affect on hotter days or cooler days? 



Option 2: Create your own psychrometer



How do you measure humidity? In this activity, you get to create your own humidity-measuring tool called a psychrometer. Another name for the psychrometer is a wet and dry bulb thermometer. This is because a psychrometer is made of two thermometers: one with wet material wrapped around the bulb and the other with the bulb kept dry. See the picture below for reference. 

In warm weather, the water in the material keeping the bulb moist will evaporate. This evaporation will cause the bulb to cool slightly. Think of when you get out of the shower or the pool--you were warm when you went in, but as the water dries off your skin, you might get a little chilly! Because of this cooling effect from the evaporation, the wet bulb will actually have a lower temperature than the dry bulb. Let’s test it out!



YOU WILL NEED:

* Two identical thermometers

* Gauze or cotton balls

* Water

* Rubber band

* Board or sturdy piece of cardboard

* Tape 

* Thick string or wire


Here's what to do!

1. Place both thermometers outside right next to each other for 15 minutes. Check to make sure that they both say the same temperature. This will ensure that they both work identically. 

2. Wrap gauze or cotton balls around the bulb of one of the thermometers and secure it with the rubber band. Dip the gauze-wrapped bulb in water. 

3. Tape both thermometers to a sturdy piece of cardboard. They should be parallel to each other with both bulbs hanging off the end of the board. Make sure they are very secure!

4. Punch a hole in the end of the cardboard opposite the bulbs. Tie a string through the hole, about a foot long. Make sure the string is tightly knotted. 

5. Now for the fun part! Go outside in an open space and START SWINGING! Hold on tight to the string and swing the psychrometer around for 2 minutes. The swinging will help the water surrounding the wet bulb evaporate quickly. 

6. Stop swinging every 30 seconds and check the temperatures. Eventually, the wet bulb temperature will quit lowering and level off. Once the wet bulb temperature has leveled off, record the temperature for the both the dry bulb and the wet bulb. 

7. Now to find the relative humidity, you subtract the wet bulb temperature from the dry bulb temperature.

Example: 

Dry bulb = 22 degrees Celsius 
Wet Bulb = 17 degrees Celsius
22 - 17 = 5
Temperature difference = 5



8. Now that you have the difference, you consult the psychometric chart to find the relative humidity. The video below contains the psychometric chart and provides an example of how to calculate relative humidity based on your findings. 

9. Use your new psychrometer to track the relative humidity throughout the summer! 



References: 

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Weather_p017.shtml#summary

http://www.livescience.com/40663-measuring-relative-humidity-science-fair-projects.html

https://en.wikipedia.org/wiki/Hygrometer#Psychrometers

https://en.wikipedia.org/wiki/Humidity



Image and Video Credits, in order of appearance:

Draper, John William. 1861. Psychrometer, “A textbook on chemistry”.  Uploaded from Wikimedia Commons on 6/19/2016. https://commons.wikimedia.org/wiki/File:Psychrometer1861.png.  Public Domain Image.

Rafalik, Christopher.  “Calculating Relative Humidity using Sling Psychrometer” Published 11/15/2013. Accessed 6/19/2016.  https://www.youtube.com/watch?v=14Q3-VtVDAI.

Author: Maddie Van Beek

This week in Fargo has been incredibly windy! Instead of complaining, let’s embrace the wind and do some windy-day activities! 


What is wind? Another word for wind could be gust, breeze, or gale. Dictionary.com defines wind as air in natural motion that moves along the earth’s surface.


Listen to Hank Green’s explanation of wind in this video to find out more:

Now that you’ve watched the SciShow episode on wind, write down your definition of wind in your own words. 


Follow-up questions:

1. How is wind created? 
2. What is the point of wind? (Hint: What is wind trying to create/help the surrounding area reach?)
3. How is wind destructive? 
4. Can wind be a good thing? 

Wind as power
Although sometimes wind can be a nuisance, it can actually help us, too. Click the link below to learn more about how wind can be used as a source of renewable energy. Take the quiz at the end to check your understanding. ​

Now that you know how wind is created and how it can be beneficial for us, let’s analyze what wind does to the air around us. 


Windchill
How does wind affect the temperature? That’s kind of a trick question. Wind doesn’t actually change the air temperature, but it does make the temperature feel colder than it actually is. If you’ve lived in the midwest, you’ve probably heard a lot about windchill. Windchill is a temperature that conveys what the air around us feels like due to the wind. Wind makes the air feel colder than it actually is. The windchill temperature is always lower than the actual air temperature. Windchill is noticed more in cooler climates during colder temperatures. 


Now that you understand a little bit more about what wind is and how it is created, let’s move on to our activities for today. First, you are going to compare the temperature versus the windchill and create a visual for comparison. 


YOU WILL NEED:

• A computer with internet 
• Paper
• A red pencil and a blue pencil 

Here’s what to do!

1. Check the temperature, windchill, and wind speed and write down each in the chart. You can use weather.com or any other weather website. Make sure you’re checking the weather in your city or town! When you record your findings, use the chart below for reference.

2. Create a graph. The X-axis should be the date, and the Y-axis should be the temperature. Each day, you will check the temperature and the windchill at the same time. If you check the temperature and windchill at 8am on Day 1, continue to check the temperature and windchill at 8am each day. Use the graph below as an example:

3. Create a graph to show the temperatures you record. Use a red pencil for temperature and a blue pencil for windchill. 


4. At the end of two weeks, analyze your graph. When was the temperature and windchill most similar? When was it the furthest apart? Did stronger winds affect the windchill more than lighter winds? What about the direction the wind was coming from? 


For your second activity, you are going to build your own wind-powered race car! 


YOU WILL NEED:

• Plastic straws or coffee stirrers
• Popsicle sticks
• Lifesavers
• Scotch tape
• Aluminum foil
• Coffee filters
• Tissue paper
• Plastic wrap
• Stopwatch

Here’s what to do!

1. Think about a car. What are the most important parts of a car in order for it to function? 
2. The car you’re making today won’t have a motor and it won’t run on electricity. It’s going to run on wind! In order to make the most of the wind energy, you will need to create some sort of wind-catcher or sail for your car. Think about the materials that would work best to catch wind. 
3. Use paper and pencils to make a sketch of your car. 
4. Select the materials you would like to use for your car. Use the plastic straws or stirrers for the axles, and use the Lifesavers for the wheels. Other than that, use your imagination to construct the best car possible! Your car doesn’t necessarily have to look like a car, but it needs to be able to roll, and it needs to be able to be moved by wind. If you need a little help, check out the image below as an example. ​

5. After you’re done building, test it out! Take it outside to see if your car will roll with the wind. If it’s not windy outside, just use your breath. If your car does not roll, take it inside and make adjustments. 

6. Once you have a car that rolls, use the stopwatch to time how long it takes to roll 10 feet. Can you make it go any faster? Have your friends build cars and race them!

​7. After you’re done racing, analyze your results. Which materials worked best for the wind-catchers? Why do you think that is? 



References
http://stem-works.com/external/activity/199
https://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_sailcars/cub_sailcars_activity1.xml
https://en.wikipedia.org/wiki/Wind_chill

Sometimes the weather doesn't behave the way you want it to. In Fargo this weekend, it was icy and sleeting. Yuck!
​
Today, we are going to do a few science activities that allow YOU to control the weather!
​
Fog in a jar
In this activity, you will see how cold air and warm air creates fog.

What exactly is fog? Fog is actually very similar to a cloud, except it's near the ground. Both fog and clouds are actually tiny droplets of water in the air. There are many different types of fog and ways that fog can form, but all kinds of fog form because of a temperature difference between the air and the ground.
​
Check out the link below to learn about some common types of fog:
https://weather.com/science/news/how-does-fog-form-20131010


Now that you know a little bit about fog and how it forms, you get to create your own!


YOU WILL NEED:
* Jar
* Strainer
* Ice
* Warm water

As you may know, tornadoes are known for their funnel shape and their power of destruction. Most tornadoes form from thunderstorms. Warm air and cool air meet, and sometimes a swirling mass is created and escalates into an even more violent storm. Another name for the shape of a tornado is a vortex. Vortexes also appear in black holes or whirlpools. You are going to create your own vortex today to simulate a tornado.


Check this link out to learn how more about tornadoes form:
http://eschooltoday.com/natural-disasters/tornadoes/how-do-tornadoes-form.html


YOU WILL NEED
* 2 Liter bottle
* Large pitcher
* Water
* Stopwatch

Here's what to do!

1. Fill the 2 liter bottle 3/4 full of water.

2. Your challenge is to identify which way water escapes the bottle the fastest--when it’s swirling like a tornado, or when it's allowed to just fall through without swirling.

3. Flip the bottle upside-down over the pitcher. What happens? Not much. You’ll see the water pass from the bottle to the pitcher. You might hear a kind of glugging noise as the water escapes the bottle.

4. Pour the water from the pitcher back into the bottle. This time, you are going to time how long it takes for the water to pass from the bottle to the pitcher, so get your stopwatch ready!

5. Flip the bottle and time how long it takes for the water to empty into the pitcher. Record your result, then pour the water back into the bottle.
​
6. Now, it's time to create a tornado! You’ll flip the bottle again, but this time swirl the bottle in a clock-wise motion until you see a tornado form. You should be able to see the vortex right in the middle of the bottle. Did the water seem to fall through quicker or slower this way? Try it again and time it! Which way was faster?


You may have noticed that water fell through to the bottom bottle much faster when it was swirling. This is because as the water falls from the top bottle to the bottom bottle, the air at the bottom needs to get to the top, to make room for that water. The vortex that you created by swirling the water creates a tunnel for the air to move to the top bottle at the same time that the water is moving to the bottom bottle. When you flip the bottles without swirling the water, there’s no pathway, so the water and air have to take turns falling through the neck of the bottle, hence the glug-glug noise.


Extension: Create a tornado-simulator that you can use over and over!

YOU WILL NEED
​
* Two 2 liter bottles
* Water
* Food coloring
* Super Glue
* Duct tape


1. Fill one 2 liter bottle 3/4 full of water.

2. Add food coloring of your choice. You could even add glitter or confetti!
​
3. Carefully line the mouth of the bottle with super glue. Place the mouth of the second 2 liter bottle on top of the mouth of the first 2 liter bottle and hold for 30 seconds. Leave the bottles alone while the glue dries for 20 minutes.

4. Tape around the necks of the bottles. Make sure to use a lot of tape so the bond is secure! It should look like this: 

5. Once your bottles are securely taped, try out your tornado! Flip the bottles upside-down and swirl them just like you did before to get the vortex going.


For another weather-related activity, check out our blog about air masses: http://discoveryexpress.weebly.com/blog/the-science-of-air-masses-what-happens-when-air-masses-collide




References:
http://www.universetoday.com/85349/how-does-fog-form/
http://www.funology.com/london-fog-anywhere-you-want-it/
https://weather.com/science/news/how-does-fog-form-20131010
https://www.stevespanglerscience.com/lab/experiments/tornado-in-a-bottle1/

Author: Maddie Van Beek

Fargo is FREEZING right now, so in honor of the arrival of sub-zero temperatures, we are going to have some fun with ice!


Build your own ice!

Author: Maddie Van Beek

Before we get going, think about these questions: How often do you watch the weather on TV? What kind of weather conditions have you seen reported? What kinds of weather conditions have you experienced in your lifetime? How has weather impacted your life? 


Get your brain warmed up! Write about a specific weather memory. 


Make a connection: Why would you need to pay attention to the weather? Can you think of a time that knowing the approaching weather would be important? 


Predict: Before you read ahead, hypothesize what do you think creates or influences weather conditions. Write down any guesses you think of! 


When you were thinking of what might influence or change the weather, did you ever think of air masses? Air masses are extremely important to consider when predicting what the weather may be like! 


According to education.com, an air mass is a large body of air with consistent temperature and humidity. When air masses form, they are taking on the temperature and humidity characteristics of the region they are in. The density of an air mass depends on the temperature and humidity levels. Warm or humid air masses are less dense then cold or dry air masses. 

Does it surprise you that humid air is less dense than dry air? 

This is because a molecule of water has a smaller mass than a molecule of oxygen or nitrogen (a large percentage of dry air molecules are nitrogen). 

But what happens when two different air masses meet? That’s our focus today! Think of oil and water as two separate air masses. If oil represented the warm air mass and water represented the cold air mass, what would you see happen? A boundary would form between the oil and water, and the oil (warm air) would float above the water (cold air). 

Here’s a little more information about fronts:

“Vilhelm Bjerknes (1862-1951), a Norwegian physicist and meteorologist, coined the term front to describe the boundary between warm and cold air masses. The leading edge of a warm air mass advancing into a region occupied by a cold air mass is called a warm front. A cold front occurs when a cold air mass advances into a region occupied by a warm air mass. If the boundary between the cold and warm air masses doesn't move, it is called a stationary front. The boundary where a cold air mass meets a cool air mass under a warm air mass is called an occluded front. At a front, the weather is usually unsettled and stormy, and precipitation is common." 

Here is a visual to help you understand the difference in air movement during cold fronts and warm fronts:

Analyze the visual and explain what you see.

As the warm front approaches, there may be fog or increasing rainfall, and thunderstorms may form, as well. This is due to the (usually) higher humidity in the air of warm fronts compared to that of cold fronts. Because warm air is less dense than cold air, the warm air rises as it runs into the cold air, which is followed by condensation and cloud-forming. 

Similar events happen when a cold front encounters a warm front, except they happen more quickly. Because cold air is denser than warm air, cold fronts are able to force warm air out more quickly. The cold air pushes the warm air upwards, which may be followed by precipitation or storms due to moisture in the air. 

Don’t quite get it? Try out this air mass activity to help you better understand air masses before we move on! 

Air Mass Activity

Check out this video to see a demonstration similar to the activity we will do next!

Here’s another similar example. Think about how this demonstration is similar to the one we already watched. What did these experiments have in common? What are they demonstrating? How are the demonstrations different? Do the differences show us different things, or are they basically two different ways to show use the same concept? Explain. 

Let’s try this on our own! 

Our task today, using food-colored cold and hot water as a visual, is to find out what happens when a warm front and a cold front collide. 

Hypothesize: What do you think will happen when you combine warm water and cold water? Will they mix immediately? If not, how long do you think it will take to mix? 


YOU WILL NEED:

• Writing utensil
• Paper
• Blue crayon or marker
• Red crayon or marker
• 10-gallon aquarium or container
• Piece of cardboard
• Scissors
• A large spoon
• Five gallons of very cold water (you may refrigerate the water in advance or put it in the freezer to chill it) 
• Blue and red food coloring
• Five gallons of very hot water (you may use the stove or microwave to heat the water, but ask an adult for help) 
• Timer 

HERE’S WHAT TO DO!
1. Before we start the demonstration, use a writing utensil to draw seven pictures of the aquarium we will be using. Label the pictures 0 minutes, 1 minute, 3 minutes, 5 minutes, 7 minutes, 10 minutes, and 15 minutes. You will be using these rectangles to create visuals of what you see for the next 15 minutes.

2. Measure the tank’s width and height, and then use those measurements to cut a piece of cardboard of identical measurements. Use the ruler to draw a straight line where you will cut the cardboard in order to make sure your piece of cardboard is cut as exactly as possible. 

3. Place the piece of cardboard in the middle of the aquarium so that it fits snugly and can stand on its own. From an aerial view, you would see something like this:

4. Make sure the cardboard fits snugly, as it needs to keep water from passing through the center of the aquarium for at least one minute! 

5. Next, grab your container of cold water and your container of hot water. Color your cold water with blue food coloring and your hot water with red food coloring. Add the desired amount of food coloring to the water and mix in with a large spoon. 

6. Once the water is colored, the cardboard is in place, and you have your drawings ready, fill the left side of the tank with the cold, blue water.

7. Now, fill the right side of the tank with the hot, red water.  

8. Remember, the blue water represents a cold air mass and the red water represents a warm air mass. 

9. Using the drawing labeled 0 minutes and the red and blue markers, sketch what the tank looks like right now. Do this quickly--it does not have to be perfect. 

10. Finally, carefully remove the cardboard from the tank and start your stopwatch. 

11. Using your pre-labeled drawings, sketch what the tank looks like at 1, 3, 5, 7, 10, and 15 minutes.
 
12. Organize your pictures in chronological order and analyze the sequence. What happened initially when you removed the cardboard barrier? What happened as time went on? Did the “air masses” stay side by side, or did they shift? Describe the movement. Explain the behavior you observed. 


Extension: Create captions that describe what is happening for each visual you created. 


YOU SHOULD KNOW: 

What is an air mass?

What is a cold front?

What is a warm front? 

What happens when two air masses collide? 





References: 

http://ww2010.atmos.uiuc.edu/(Gh)/guides/crclm/act/arms.rxml

http://sciencenetlinks.com/lessons/air-masses/

http://www.education.com/science-fair/article/when-air-masses-collide/

http://www.education.com/science-fair/article/fronts-moving-air-masses/

http://en.wikipedia.org/wiki/Cold_front

http://en.wikipedia.org/wiki/Warm_front

http://en.wikipedia.org/wiki/Humidity

 Tornadoes are some of the most violent and dangerous storms.  While they are usually short-lived (most last less than 10 minutes according to the National Weather Service), some can last more than one hour.  Even in a short time on the ground tornadoes can take lives, cause terrible injury, and do millions of dollars worth of damage.  So why do tornadoes form in the first place?

Before we discuss how tornadoes form, it’s important that we understand thunderstorms.  Thunderstorms occur when warm, moist air rises from the surface of the earth, cooling and condensing into clouds as they reach higher altitudes where the temperatures are colder.  These clouds then produce rain, causing rapid downward-moving cool air known as a downdraft.  Usually this downdraft and its cool air quench the updraft, and the storm ends.  However, occasionally a thunderstorm will develop into a much stronger, more violent storm called a supercell. 

Supercells are different from normal thunderstorms because they rotate; they form when the air near the Earth’s surface and the air at higher elevations are moving in different directions, causing internal rotation of the clouds.  This phenomenon is called wind shear, and frequently happens when cool, dry air moving south from Canada reaches areas where warm, moist air is moving north from the Gulf of Mexico. 

Because of this wind shear, the air begins to rotate horizontally.  This combined with the strong updrafts from the rising warm air near the Earth’s surface cause the rotation to become vertical; this vertical rotation is called a mesocyclone. 

As the storm intensifies, the cooling rain and resulting downdraft begin to drag the mesocyclone downward toward the ground.  Continuing updrafts intensify also, creating an area of low pressure near the ground, dragging the rotating mesocyclone down further.  Eventually this rotation touches the ground, officially becoming a tornado.  

BUILD A WATER TORNADO!

Here’s what you’ll need:

1.       Two empty, clear 2-liter soda bottles

2.       Duct tape

3.       Super glue (you could use calking from a hardware store also)

4.       Enough water to fill one soda bottle about ¾ full. 

Here’s what you need to do:

1.       Remove the caps from your bottles

2.       Fill one of your empty bottles with water until it is ¾ full

3.       Turn the other empty bottle upside down, and use the super glue or caulk to glue the openings of the two bottles together.

4.       Wrap the duct tape around the openings of the bottles and up the sides of each bottle, so that the duct tape is wrapped securely around not only the necks of the bottles but also at least ¼ of the main body of each bottle.

5.       Allow the glue to dry for at least 20 minutes

6.       Once the glue is dry, rapidly turn the bottles over so that the water is at the top.  Do not shake or rotate the bottles.

7.       When all the water has gone from the top bottle to the bottom, write down your observations

8.       Next, turn the bottles over again, but this time swirl the water in a clockwise motion as you turn the bottle over.

9.       When all the water has gone from the top bottle to the bottom, write down your observations

What happened the first time you turned the bottles over?  What about the second time? 

What effect did rotating the bottles have?  How is this like how a tornado forms? 

Be sure to write down all your answers and observations!

To see a hot air balloon in flight is truly something to see!  A typical hot air balloon is 60 feet wide, 80 feet high, contains 77,000 cubic feet of air, and weighs about 800 pounds without passengers (skydrifters.com, sundanceballoons.com)!  So how do these behemoths manage to float so gracefully through the air?

As it turns out, hot air balloons work based on the same principle that causes air currents and wind, thunderstorms, and tornadoes.  They work because hot air rises, while cool air sinks!  If you watch a hot air balloon being filled for flight, you’ll see a large gas burner forcing hot air into the opening at the bottom.  This allows the balloon to fill with air that is hotter than the air surrounding the balloon.  As the air inside the balloon rises in temperature, the balloon rises off the ground!  Have a look at the YouTube video presented below  to watch some hot air balloons being filled for flight (this great video was uploaded to YouTube by Geoffrey McKay--we did not make this video!!).  You’ll notice at the beginning of the video that cool air (the same temperature as the surroundings) is being blown into the balloon with a fan—this fills the balloon with air, but does not cause it to lift.  Only when the balloon is filled by the burners does it lift off the ground.

So why does hot air rise, while cool air sinks?  First, let’s discuss what air really is.  Air is a mixture of different gaseous elements that surround the planet because of gravity (for a more thorough review, see our previous blog, “Can Anything Really be Lighter Than Air?”).  We call this layer Earth’s atmosphere.  The density of this layer of gas—that is, the number of molecules per unit volume—depends on the temperature of the gas.  As the gas heats up, the molecules move faster and faster, and therefore they spread out, making the gas less dense.  As the gas cools down, the molecules slow down and thus get closer together, making the gas denser because there are now more molecules per unit volume. 

This phenomenon is responsible for much of the weather on our planet:  the air closer to the Earth heats up, as the temperature is warmer close to the ground.  This air begins to rise, causing updrafts (you can see these updrafts clearly in the clouds during the summer, when the air near the Earth’s surface is very hot).  These are called thermal columns, because the heated air rises in a column.  As the air gets farther and farther from the Earth’s surface, it begins to cool.  This cooler air then sinks back down to Earth’s surface, and the whole cycle begins again.  This is called atmospheric convection. 

Now that we understand why hot air rises, we can begin to understand why a hot air balloon is able to fly.  The material the balloon is made of is able to keep all that hot air inside the balloon, separated from the cool surrounding air.  This makes the air inside the balloon much less dense than that surrounding it; in effect, the hot air balloon is like a giant bubble of less dense gas!  This is what makes it float up off the ground—it’s just like a bubble of less dense air rising through more dense water! 

TRY FLYING YOUR OWN HOT AIR BALLOON!

Here’s what you’ll need:

1.       One or more ignitable floating lanterns, such as Sky Lantern® (available at www.skylanterns.us, or at your local fireworks outlet)

2.       Matches or a candle lighter

3.       A fire extinguisher...just in case!

NOTE:  Be sure to do this on a calm day!  Wind will interfere, and will increase the risk of starting a fire.  Also be sure that your area does not have burning restrictions!

Here’s what you need to do:

In general, just follow the instructions on the lantern’s packaging!  You will light the fuel below the large paper lantern using your matches or lighter, being careful not to burn the lantern.  Allow the lantern to fill with hot air, let it go, and watch it fly!

CHALLENGE:

Now that you’ve seen a paper lantern fly, try to make your own!  Use light tissue paper, some strong glue, and some very thin wire for the base.  Use old newspaper soaked in vegetable oil for the fuel.  Try your lantern in an open area, far away from any homes! 

If you make a paper flying lantern, take pictures or video, and share with us!  Go to https://www.facebook.com/discoveryexpresskids, and post them on our page!!