Don’t worry to much if you don’t have whole milk or heavy cream. Nearly any milk will work and you can substitute half-and-half for the cream. Ideally you want ingredients with a high fat content because these will create a creamy texture when cooled. Remember that we’re just experimenting here, so try what you have on hand!

Ingredients

• 1/2 cup milk (Whole or 2% work best)
• 1/2 cup heavy cream (optional)
• 1/2 teaspoon vanilla
• 1 tablespoon sugar
• 4 cups crushed ice
• 4 tablespoons salt
• 2 quart size plastic bags
• 1 gallon size plastic freezer bag
• a hand towel or gloves to keep fingers from freezing as well

Basic Directions

Begin with mixing the milk, vanilla and sugar together in one of the quart size bags. If you want, you can mix this in a bowl first so that you get all the sugar dissolved. Seal the bag tightly, you want to try to get as much of the air out of the bag as you can. Too much air left inside may force the bag open during the mixing stage.

Place this bag inside the other quart size bag, again leaving as little air inside as possible and sealing well. By double-bagging, the risk of salt and ice leaking into the ice cream is minimized.

Put the two bags inside the gallon size bag and fill the gallon sized bag with ice, then sprinkle salt on top. Again, squeeze out as much air as possible and then seal the bag. Wrap the bag in the towel or put your gloves on, and shake and massage the bag, making sure the ice surrounds the creamy mixture. Five to eight minutes should be enough time to allow the mixture to freeze into ice cream.

When you are all done carefully open the bags and extract your ice cream. Enjoy!

If you’d like to experiment a bit more you can try substituting a mixture of heavy cream and your choice of milk. Mix up a few different batches and compare the texture of ice cream. Which to you think will have a smoother texture?

We suggest using freezer bags because they are thicker and less likely to develop small holes, allowing the bags to leak. You can get away with using regular plastic bags for the smaller quart sizes, because you are double-bagging. If you plan to do this indoors, we strongly recommend using gallon size freezer bags.

What does the salt do?

Salt forces the ice surrounding the bag of ingredients to melt. This “brine” solution or liquid that forms in the gallon bag absorbs the heat from the ice cream mix and gradually lowers the temperature of the mix until it begins to freeze.

If there were no salt added to the ice, it would melt at 32 degrees Fahrenheit and eventually the ice water and mix would come to equilibrium at 32 degrees. The ice cream mix, however, does not begin to freeze until its temperature falls below 27 degrees. Therefore, in order to freeze the mix, we need to add salt to the ice to lower the freezing temperature.

With 4 tablespoons of salt mixed with our ice, the brine temperature should remain constant at around 8 to 12 degrees Fahrenheit. This will give the rapid cooling and freezing that is essential to making smooth creamy ice cream.

What you need:

• 1 cup hot water
• 1.5 tsp. Borax (non-toxic/available by laundry detergents)
• 2 cups clear glue
• 2 cups warm water
• 1 tsp. liquid watercolor

What to do:

1. Mix 1 cup hot water and 1.5 tsp. of Borax until dissolved. Set aside.
2. Mix 2 cups of clear glue and 2 cups of warm water together in a plastic bowl.
3. Using a metal spoon, slowly pour Borax mixture into the glue mixture while stirring quickly. Stir until the mixture leaves the side of the bowl. Slime will be sticky. Knead the mixture until it is no longer sticky. The more you work with it the easier it will become.

What’s the science?
Slime is an excellent example of a polymer. The word polymer comes from the Greek language from poly “many” and meros “parts”. Polymers are large molecules consisting of repeating identical structural units connected by covalent chemical bonds. Polymers can be naturally occurring or manmade. Manmade polymers are materials like nylon, polyester, and polystyrene. Examples of naturally occurring polymers are proteins in our body like tubulin and actin. These proteins make up microtubules and microfilaments that serve as structural components within our cells.

Storage and Safety Guidelines:
Store Slime in an airtight container for about 3 weeks of use. Slime is non-edible. When you are through with it, discard in a trash container. Do not wash down the drain.

With just a few gumdrops and some toothpicks you can build some pretty cool structures that are amazingly strong yet simple in design.

What you need:

• Box of Toothpicks
• Bag of Gumdrops

What to do:

1. Use gumdrops to connect 5 toothpicks in a ring. This is your base.
2. Use 2 toothpicks and 1 gumdrop to make a triangle on one side of the base.
3. Repeat all the way around the base until you have 5 triangles.
4. Use toothpicks to connect the gumdrops at the tops of the triangles. Now how many triangles do you have?
5. Push 1 toothpick into each of the top gumdrops.
6. Use one last gumdrop to connect these toothpicks at the top.

What’s the science?
Engineers often use triangles when they design buildings. Did you notice that your dome is made up of lots of triangles? That’s because triangles are stable shapes. That means they don’t bend, twist, or collapse easily when you push on them. A square is not as stable as a triangle. Test it. Make a square and a triangle out of toothpicks and gumdrops.  Press down on one corner of each shape. How do the two shapes compare? Does one bend, twist or collapse more easily than the other?

What will happen if . . .

• you make a base with six sides instead of five sides?
• you build squares rather than triangles on top of the base?

Choose one thing to change (that’s the variable), and predict what you think will happen, then test it.

Recipe for Oobleck

To mix up some Oobleck grab a box of cornstarch, some water and a mixing bowl. In general, a mixture of about 1.5 cups of cornstarch to 1 cup of water is a good starting point. You will have to tweak these amounts to get the perfect mixture. Keep in mind that the mixing process can get messy so be prepared to clean up.

• Cornstarch
• Pitcher of water
• Aluminum pie pans
• Measuring cups
• Mixing spoon
• Newspaper for covering tables
• Food coloring or tempera paint (for fun)

Pour the cornstarch into a large mixing bowl and slowly add the water. You are shooting for a mixture that feels kind of like honey and tears a bit when you run your hands across the top. You will have to experiment with more or less cornstarch or water until you get the right mixture. If you want to color your Oobleck add some tempera paint. You can use food coloring if that’s all you have on hand. Food coloring tends to stain more than the paint, especially if you have a spill while preparing your Oobleck.

One thing to keep in mind is that Oobleck is a suspension, not a solution. The cornstarch does not dissolve in the water like salt or sugar would. Instead, the tiny starch particles are suspended in the liquid. If you let it sit long enough in a glass, the cornstarch will settle to the bottom leaving a layer of clear water on the top. This is why it is very important to not pour Oobleck down the drain. Should the suspension separate in your drain pipes, you will be left with a hard clump of cornstarch that will block the drain. The best way to get rid of you Oobleck is to simply put it in your trash can.

What does non-Newtonian mean?

All fluids have a property known as viscosity that describes how the fluid flows – commonly thought of as how thick or thin a fluid is. For instance, honey is much more viscous than water. When a fluid’s viscosity is constant it is referred to as a Newtonian fluid. Oobleck is an example of a fluid whose viscosity is not constant, it changes depending on the stress or forces applied to it. If you poke it with your finger and apply a large force, it becomes very viscous and stays in place. If you gently pour it, applying little force, it will flow like water. This kind of fluid is called a dilatant material or a shear thickening fluid. It becomes more viscous when agitated or compressed.

Another non-Newtonian liquid is ketchup. Ketchup behaves in just the opposite way from oobleck. It becomes less viscous when agitated. Liquids like this are called thixotropic. If you leave a bottle of Ketchup on a shelf, it becomes thicker or more viscous. Nearly everyone has experienced this while trying to pour the liquid from a new bottle – it refuses to move. If you shake the bottle or stir it up it becomes less viscous and pours easily.

Why does Oobleck behave the way it does?

The most generally accepted explanation for the behavior of Oobleck is offered by Cary Sneider in “Oobleck: What do Scientists Say?”. When sitting still the granules of starch are surrounded by water. The surface tension of the water keeps it from completely flowing out of the spaces between the granules. The cushion of water provides quite a bit of lubrication and allows the granules to move freely. But, if the movement is abrupt, the water is squeezed out from between the granules and the friction between them increases rather dramatically.

Experiments to try

The first thing you have to do is simply place your hands into the Oobleck and start squeezing it. Have some fun! Try to make a ball by moving it around quickly in your palms. Once you stop applying pressure to the mixture it will flow out of your hands like a liquid.

Try filling a pie plate with a think layer of Oobleck and then slapping the surface with your open hand. Because of the dilatant properties, becoming more viscous when a force is applied, the liquid will all stay in the plate. Try the same experiment with water and compare the results!

If you have a lot of cornstarch and a small pool (or a large one like in the video) you can supersize this experiment. Since the liquid becomes more viscous when pressure is applied you can actually walk or run on the surface without sinking. Of course, once you stop moving you will begin slowly sinking into the liquid.

Another fun experiment is to fill the cone of a speaker with some Oobleck. Connect the speaker to a low frequency sound source and watch as the Oobleck seems to come alive. Typically low frequencies get the fluid up and moving better than higher pitched sounds. A plastic subwoofer works the best, or you can use a sheet of plastic wrap to protect a paper cone speaker.

Film canister rockets are always pretty amazing considering all that powers them is a little bit of Alka-seltzer and water. The launching time is always a bit unpredictable and that just adds to the fun.

What you need:

• Paper, Index cards or cardstock,
• Translucent film canister, Tape,
• Scissors, Effervescing antacid tablet,
• Water and Paper towels

What to do:

1. Wrap and tape a tube of paper around the film canister. The lid of the canister goes down.
2. Cut fins from the index cards and tape to the rocket.
3. Make a nose cone by cutting a circle out of paper. Cut out a pie shape from the circle and twist the paper into a cone. Tape the cone together. Then tape it on the open end of the paper tube.
4. Turn the rocket upside down and fill the canister 1/3 full with water.
5. Work quickly! Drop in a 1/2 tablet and snap the lid on tight.
6. Stand the rocket upright and stand back!

CAUTION: Be careful when launching your rocket. Stand back and don’t point it at anyone.

What’s the science?
As the antacid tablet “fizzes” carbon dioxide inside the canister, pressure from the gas builds and eventually pops the lid off. The amount of force, or push, created is related to the amount and speed of gas and water propelled from the canister.

What will happen if…

• you change the design of your rocket?
• you use more or less “fuel?”
• you use hot or cold water?

Choose one thing to change (that’s the variable), then predict what you think will  happen and test it.