Summer Science: Making Ice Cream

It's time for some ice cream! Wait...wait...no need to pull out the industrial-sized, hand-cranked monster from the 1940's. You don't even need to make that trip to the grocery store. With some ingredients and supplies that you have right in your home, you can make your very own ice cream. Of course, it helps if you know a little science. That's what I'm here for! Forget Ben and Jerry's! So long Häagen-Dazs! Hasta la vista Baskin-Robbins! Say hello to my little friend...Ziploc Bag Ice Cream!

Here's What You Need

• 1 cup of Half & Half
• 6 tablespoons rock salt
• 2 tablespoon sugar
• 1 teaspoon vanilla extract
• Ice 
• 2 Ziploc freezer bags (two different sizes, 1 gallon size and 1 quart size)

 Here's What You Do

1. Fill the larger (gallon size) Ziploc back 3/4 full with ice. Sprinkle the rock salt over the ice, seal the bag (very important), and put it to the side. We will use this a little later.
2. Put the Half & Half, the vanilla, and the sugar in the smaller (quart size) bag. If you want to add a couple of special mix-ins (like chocolate chips), place them in the bag also. Squeeze out the excess air, seal the bag (once again...very important), and shake it around to mix the ingredients. Believe it or not...this liquid mixture will become solid ice cream!
3. Open the large bag of ice and place the small bag inside. Seal the large bag (still very important). Now, it's time to churn the ice cream. Gently turn, flip, and knead the bag. The goal is to turn the liquid ice cream mixture into solid ice cream. That's the science part! The trick is to make the mixture very cold. Trust me...it's going to get very cold! In order to avoid frozen fingers, I suggest you wrap the plastic bag in a towel and take turns churning the ice cream with a partner. Make it a whole family activity!
4. The time it takes to turn your ice cream mixture into a solid depends on how well you churn. In my experience, it takes about 10 - 20 minutes of churning to produce good ice cream. When you think your ice cream has hardened, open the large bag and remove your bag of ice cream. If it is ready, your bag will be stiff. If you didn't churn long enough, you might notice liquid inside the bag (more like ice cream soup then ice cream). If this happens just stick it back in the ice, seal the bag, and churn a bit more. If your ice cream is ready, use a cloth to wipe any salt water or rock salt off the small bag (especially around the opening). You don't want salt water in your ice cream.
5. Grab a spoon, open the small bag, and dig in!

The Science Behind the Ice Cream
Who knew science was so de-li-cious?! Let's talk about some of the science behind the ice cream. You started this adventure in science with a mixture of Half & Half, sugar, and vanilla; a liquid. After all of the flip, kneading, and turning, you ended up with ice cream; a solid. If you didn't eat your ice cream fast enough, you might have noticed that some of it began to melt (solid becoming a liquid). Scientists call this shift from solid to liquid or liquid to solid a change of state. Changes of state are happening all around us all of the time. Liquid water changes into solid ice to make snow. Liquid gasoline turns into gaseous gasoline to power our cars. There are plenty of others.

Why couldn't we just use ice to freeze the ice cream? What's up with the rock salt?! Well, that's really a question of temperature. Water freezes at 32 degrees Fahrenheit. In order to freeze the ice cream, we needed temperatures lower than 32 degrees Fahrenheit. That's where the salt comes in. Salt lowers the freezing point of water. In other words, salt water freezes at a lower temperature that fresh water does. Remember, water freezes at 32 degrees Fahrenheit. Well, a 10% salt solution freezes at 20 degrees Fahrenheit, and a 20% solution freezes at 2 degrees Fahrenheit. That's why people sprinkle salt on icy sidewalks, steps, and streets. The salt lowers the freezing point of the water and causes the ice to melt.

In order for a solid to become a liquid, it must absorb energy. For a liquid to become a solid it must give away energy. Scientists call this energy heat. In this activity, the liquid ice cream mixture gave up heat energy. That energy was absorbed by the ice as it melted. By adding salt to the ice, you lowered the temperature inside the bag. In fact, the mixture of rock salt and ice gets as cold as about 14 degrees Fahrenheit (-10 degrees Celsius)! That's real cold! Just right for making ice cream!

Help NASA Learn More About the Clouds

Looking for something interesting to do with you children this summer?  Why not help NASA scientists understand the connections between clouds and the Earth's climate?  On the NASA website, they state:

It is the clouds, in part, that affect the overall temperature and energy balance of the Earth. The more we know about clouds, the more we will know about our Earth as a system! 

Just think...you can brag to all of your friends that you and your kids are part of an elite groups of scientists working on a nationwide environmental science project!

I'm sure you're wondering how you can help NASA.  After all, don't they have satellites, space stations, and lots and lots of really powerful computers?  True.  What they don't have, however, are accurate ways to quickly identify clouds around the world.  Satellites are great, but they often have a tough time distinguishing clouds from other white surfaces like snow or ice covered ground.  NASA needs you and your eyes.  NASA is in the process of recruiting people around the country to collect data about the clouds they see in the sky above their communities.  They will use your observations to help them validate satellite data and create a better picture of clouds in the atmosphere

NASA's idea isn't new.  In fact, there are all types of projects that use everyday people to collect data.  There known as Citizen Science projects.  They harness the power of the internet and large groups of people to move scientific understanding forward.  Citizen Science has helped us chart stars in the night sky (Galaxy Zoo), understand the natural world (The Great Sunflower Project), and solve puzzles (FoldIt). Now, you can get involved with citizen science with NASA's Rover or S'COOL project.

To get more information about the project, learn how to get involved, or register, visit NASA’s S’COOL Roving Observation website. If you are are teacher or a homeschooler and you want to do scheduled observations from your home or school, you can also visit the CERES S’COOL Project website. As usual, let us know about your experiences!  We love to hear about all the great science you are doing!

Hanging Out with Amateur Astronomers: The Transit of Venus

Did you miss it?  It won’t happen again for another 105 years; December 2117 to be exact.  What exactly am I talking about?  Why the Transit of Venus, of course.  On June 5, 2012, Venus, the second planet in the solar system, traveled between the Earth and Sun.  The alignment of these three celestial bodies allows anyone with a little ingenuity and a clear sky to see a clear view of Venus silhouetted against the sun.  The Atlanta Astronomy Club and Stone Mountain Park organized a public viewing event and more than 100 people gathered on top of Stone Mountain to witness the transit. The Science Wondershop teamed up with Macaroni Kids Decatur to check out this rarest of predictable astronomical events.

More then 100 people gathered at Stone Mountain to see Venus cross the Sun.

 Astronomy has always been and continues to be one of my children’s favorite areas of science. There’s just something about the planets, moons, and stars floating around in outer space that inspires lots of curiosity and questions.  When Macaroni Kids Decatur and Stone Mountain Park invited us to participate in the viewing of the Transit of Venus, my wife and I packed up the kids and made our way to the top of the Stone Mountain to take advantage of this once in a lifetime opportunity.

My daughter uses Solar Glasses to look up at the sun.

Venus began its trip across the sun at 6:03 PM.  Similar to a solar eclipse, it was impossible and dangerous to attempt to see Venus without special equipment.  The Atlanta Astronomy Club provided lots of options for safely viewing the transit.  People like Astronomy Club member, Marie Lotte,  brought specialized telescopes with solar filters, dedicated solarscopes, solar binoculars, welders glasses, and lots and lots of solar sunglasses.  Using any of these pieces of equipment, people on top of Stone Mountain could watch Venus, a tiny black dot, move slowly across the face of the sun. 

A telescope equipped with an oil filter and sheet of projection film created this image.

The Transit of Venus happens on a 243 year cycle.  The last time it happened was 8 years ago.  It will occur again in 105 years.  Besides being rare and beautiful, the event has historical significance to the astronomy community.  Early astronomers used the Transit of Venus to estimate the size of the sun and the distance between the Earth and the Sun.  Today, scientist track similar spectacles in an attempt to understand the size of our solar system and other worlds.  Yesterday, however, our world paused for a moment, looked up, and witnessed a truly fascinating lesson in the beauty of our world.  As a dad, husband, and science guy, I couldn’t have asked for a better way to spend a breezy, summer evening with my family.