General Science: What's a yeast's favorite food?

This week we learned a little bit about our tiny unicellular fungal friend, the yeast. After all, we have a lot in common: We eat, reproduce, respire...we're practically identical. So when it came to investigating which foods yeast like best, we decided to use something else we have in common: When we're done eating (and transforming the energy from food into energy our cells can use), we all release carbon dioxide. This comes in handy when we use yeast to help us make bread. It is the carbon dioxide gas that causes the bread to rise.

We compared carbon dioxide production in yeast when fed 5 different kinds of food: salt, flour, sugar, ground-up cookies, and ground up vaflim (wafers). To get an idea of which food was eaten most heartily by our yeast, we covered each bottle with a balloon. Then we sat back and watched the show. The samples of yeast fed sugar, cookies, and vaflim were the happiest, i.e. the balloons were the most inflated because of the greater production of carbon dioxide. The flour came in second place. We discussed how cookies contain sugar, and how flour, a complex sugar, can be broken down into simpler sugars. A little more work, but when you're hungry, you do what you have to. Yet one more thing we and yeast have in common...LAZINESS! Who here isn't counting down the days 'till summer vacation?!

Ice cream in a bag!

This week we did a pretty COOL trick....we made ice cream, without a freezer, without an ice cream machine. How did we do it and what does it have to do with science?

First we demonstrated that ice covered in salt will melt faster than ice alone, and most surprisingly that the liquid salt water is actually COLDER than the frozen ice. We then discussed how phase change, or matter moving back and forth between solid, liquid, and gas states, involves a transfer of energy or heat. In other words, when there is a phase change, heat is absorbed in one direction and released in the other. These ideas and observations formed the basis of our ice cream experiment.

The kids poured the ice cream ingredients (milk, vanilla, and sugar) into a small plastic bag. Then they placed this bag into a larger bag filled with a lot of ice and a lot of salt. The whole business was then wrapped in a towel and then shaken until the milk mixture solidified. The rock salt caused the ice to melt quickly and reach a sub-zero temperature, so that the resulting freezing salt water could quickly absorb heat from the milk mixture, giving you yummy, delicious ice cream or at the very least, a super-cool milk shake.



Here's the procedure in case anyone wants to try it at home.

1. Pour ¼ cup of milk into a sandwich-size zip lock bag.
2. Add 1 teaspoon of sugar and a couple drops of vanilla extract.
3. Close the bag carefully, while getting rid of the extra air.
4. Mush the bag around to mix the contents.
5. Place this bag in another sandwich zip lock bag, remove the extra air, and seal.
6. Fill a 1-gallon zip lock bag with ice and a half a cup of rock salt.
7. Place the double bagged milk mixture inside the larger bag, squeeze out the extra air, and seal.
8. Wrap each bag in a towel and mix, shake, and churn until the inner bag's contents freeze.

Tips:

* Make sure all bags are closed, especially before you start shaking up the bag of ice and salt.
* Double-bagging the milk mixture is important, to help reduce the odds of salt penetrating the bag and getting into the ice cream (yuck!).
* Err on the side of too much ice and too much salt.
* Try to keep the milk mixture bag in the middle of the ice, and especially in the middle of the melted salt water.
* See what happens if you add different flavors like chocolate syrup or lemon juice.

Chemistry in a bag

The kids started off with calcium chloride, sodium bicarbonate (see if your kids remember this compound's common name...it's baking soda), water, and phenol red, an indicator for acids. They put all of these materials in a plastic bag, the catch being that the liquids (water and phenol red) were first poured into plastic cups, which themselves were carefully placed in the bag. Why all the extra steps? This allowed us to measure the whole business BEFORE the chemical reactions began. After tying off the bag, the kids allowed the powders and liquids to mix, and that's when things got exciting! The kids observed many changes including: bubbles, the bag inflating, the red liquid turning yellow, and the contents both heating up and cooling down. The kids then measured the weight of the bag with its contents, and they were pretty surprised to find very little if any change. That's conservation of mass for ya! Step 2 of this experiment was breaking down the reaction into parts to see what happens when you combine different pairs of ingredients.



Chugim will run as usual next week for all groups, INCLUDING Tuesday's sessions, which will meet at their usual times.

General Science: Hunting for bacteria

Here are the results from last week's Bacteria Hunt:




Take-home message:

For the most part soap works, particularly with those bacteria samples taken from the trunk of my avocado tree.

General Science: Indicators for acids and bases

This week we learned about acids and bases and two types of indicators you can use to identify them. We began by using red and blue litmus paper to test different household liquids. We were then able to classify them as acids, bases, or neutral. However while litmus paper is useful, it doesn't tell you anything about how strong or weak a base or acid is. So, for example, while baking soda and bleach, the two bases we encountered, score the same on a litmus test, baking soda tastes mildly bitter whereas tasting bleach will land you in the hospital (hypothetically speaking, of course!). We observed that in order to appreciate this without landing in the hospital, pH paper comes in real handy.

General Science: Dry Ice

We started off the session by discussing what makes dry ice so COOL.

While it looks like regular water ice, it is actually frozen carbon dioxide. It is genuinely cooler than regular ice. That's why we ONLY handled the dry ice with tweezers. Possibly the coolest part is how it sublimes, meaning it changes directly from solid into a gas, skipping the liquid phase.

Then we demonstrated its coolness in the following ways....

• froze cooked pasta and flowers by dropping them in acetone with dry ice. (Acetone is good thermal conductor, so it gets really really cold.)

• produced a lot of spooky fog.

• "poured" carbon dioxide gas into a cup on a scale and noted that it weighed more than an equal volume of air.

• used carbon dioxide gas as a fire extinguisher (Don't panic, the fire was a single lit candle).

• measured temperature changes in water after adding dry ice.

• made the dry ice "squeal" and vibrate after pressing it with a metal spoon.

• inflated a latex glove by putting a piece of dry ice inside and then tying off the open end.

• produced a loud popping sound by placing a piece of dry ice in a small plastic container and then closing it.

General Science: The Case of the Stolen Handouts

This week we were supposed to do a fascinating investigation, Salt: What makes it taste so darn good? As usual, I placed the handouts on the table, and then left for a few minutes to gather some supplies. When the kids arrived, my whiteboard was lying on what I thought was the pile, but when I lifted it, I was quite shocked to find no paper, but a PILE OF MYSTERIOUS WHITE POWDER!!!

While the kids were checking outside for clues, I quickly dusted for fingerprints, messengered the fingerprints over to the police station, and after a lightning-fast search through their databases, they faxed me a list of suspects (further proof Raanana is in fact Israel's most efficiently-run city).

Suspects:
1) Danny Sadinoff, a real meat-and-potatoes guy who likes his gravy so much (and so thick), that he is often seen carrying a bag of corn starch. When questioned he admitted that he needed some paper to block the sun out of his office since there are no curtains.

2) Chen Sadinoff, aka babyface likes nothin' better than Cheerios with a generous sprinkling of sugar. She's known to be quite mischievous, stealing people's homework and other important documents only to scribble on them in some top secret language known only to her and her evil associates.

3) Asaf, owner of the popular Yaar Kasum stationery store: Asaf could not be found when we came to question him, but a woman who works there mentioned that she has heard him complain about my having cut back on the copies I make there. Also suspicious were the packets of baking soda sitting on the counter.

4)Me...Look, it's not surprising that MY fingerprints were found. After all, it is my kitchen. Still, some of the more cynical members of the chug had the nerve to suggest that I had planned the whole thing. Pretty ridiculous, I know.

Luckily our amateur detectives had some previous experience identifying white powders. With the help of iodine, vinegar, a microscope, and an electrical circuit run through water, they were able to identify the powder and ID the bad guys.

Turns out the powder was a mixture: salt and corn starch suggesting that it wasn't one perp but two. And, if it weren't for you meddling kids, Danny and I would have gotten away with it!

General Science: Iodine as indicator

This week the kids learned how to use an INDICATOR, a compound that will change color when it comes in contact with a particular substance. Without too much background on what starches are, the kids were given around 10 different foods to test using iodine, a compound which changes from orange to black on contact with starch. As they made their way through the food samples (testing them, not eating them), they were able to refine guesses about what starches have in common. Finally, we concluded that starches come from plants and are how plants store simple sugars.

Afterward we discussed how simple sugars are connected by chemical bonds to make complex sugars and conversely, how the chemical bonds within complex sugars are broken to produce simple sugars. The kids chewed on that for a few minutes...literally! I gave each one a cracker, and they observed how after a few minutes of chewing, they could taste the sugar that resulted from their saliva breaking down the starch.

General Science: Elements we know and love

This week we in introduced the Periodic Table of Elements. At first the kids were a bit overwhelmed by all the scary looking numbers and letters, but on closer inspection, they realized that there were a lot of elements they know quite well. After talking a bit about different elements the kids carried out an experiment in which they explored the properties of sulfur and iron using a magnifying glass, a microscope, and a magnet. They combined them, and then assessed whether they had performed a physical change or a chemical change.

Here are some of the high points of their results:

iron: black, magnetic
sulfur: yellow, smelly, not magnetic
iron + sulfur: grayish yellow, smelly, BUT easily separated from each other with a magnet

Physical or chemical....you decide!

Chemistry trivia: What are the chemical symbols for sulfur and iron? Ask your kids and let them show off their Latin!

General Science: Plant cell and animal cells...up close and personal

Last week we continued our investigations with microscopes. Having already gotten some experience with the ins and outs of using a microscope, we focused on different kinds of cells. The kids got a chance to compare plant and animal cells by extracting human cheek cells (sounds much more painful than it actually is) and onion cells (a little smelly, but otherwise no tears). We talked about how animal cells are more "blob-like," and plant cells have a rigid exterior, which makes them look like boxes or bricks.

General Science: It's a gas and "Ooblek"

For our experiment this week, we did an oldie but a goodie...what happens when you combine baking soda and vinegar?
Perhaps because of some past experience building volcanoes, the kids guessed correctly that the combination would produce, in their words, "AN EXPLOSION!!!" (Aren't you glad this happens at my house and not yours?!) But more than that, they observed that the mixture of baking soda and vinegar interacts with a lit candle differently than would vinegar or baking soda alone. Passing a lit candle over baking soda had no effect on the flame. Same deal for the vinegar alone, but when you combine the two, and you get your EXPLOSION (i.e. bubbles), passing the candle over extinguishes the flame. Why does this happen? Mixing baking soda and vinegar is a chemical reaction, and as such, produces something new, carbon dioxide. Those are your bubbles, and they have the property of putting out a fire. That's why they put it an actual fire extinguishers. Cool, huh!?

Afterward the kids mixed cornstarch and water to create a really neato substance. What's so cool about "oobleck?" Well, it behaves like a liquid until you apply pressure to it. Then it behaves like a solid. Check out this video to see what I mean. http://www.instructables.com/id/SMEOL98FIWH3SZ4/

General Science: I can't believe it's butter!

This week the kids learned how to make butter. It's pretty simple, really...you take some heavy cream at room temperature, put it in a jar with a marble, and shake it up until it turns into butter. The kids made observations of the contents of the jar every 3 minutes, noting when the cream changed from liquid to solid. We discussed why this happens, and how it is COMPLETELY different from what we learned last week about phase changes. The reason the cream turns into butter is NOT because it is losing heat, but rather because the tiny fat bubbles that are suspended in the cream gradually stick together until the mixture separates into butter, a solid, and buttermilk, a liquid.

Finally, we added a little salt to the butter, spread some on a baguette, and had a yummy treat! Of course, eating the bread and butter was preceded by an interesting conversation about what the threshold amount of bread is requiring a bracha. Someone in the group suggested 56 grams. (Is this true and are there other considerations besides the mass? I don't know, and I'd appreciate more information from someone who does.) In any case, we measured a slice of bread on the triple beam balance and found it weighed about 10 grams less. Most kids preferred the baguette, and while we didn't take measurements, I would guess that they consumed at least 56 grams.

Three cheers for torah u'mada!

General Science: Vanishing ice cubes

This week we started talking about states of matter and observed and documented temperature changes in ice cubes as we heated them in a pot on the stove. At first the kids started off working in pairs, but ran into several problems. I gave each group 2-3 ice cubes and they went from solid to gas in under 3 minutes (the ice, not the kids), plus keeping track of the time and taking measurements was very difficult to do consistently with just 2 people. So while we were able to see that the temperature went up, we didn't learn much about what happened along the way. As a group we brainstormed how to redesign the experiment so that we could see whether the temperature goes up consistently or not. We decided to a)start with more ice, so that is would take longer to melt and b) work as one big group with each kid being responsible for 1 measurement. This worked great and after conducting the experiment, the kids graphed their data and noted some interesting, even surprising results. The temperature did go up, but not in a straight line. Along the way, there were periods of time where the temperature didn't change much at all. Even more surprising was one example of the temperature going down. Were these results because of mistakes we made, or do they reveal something cool about phases changes.....stay tuned!

General Science: The Right Stuff

This week the kids had to design a spacesuit that could withstand the intensely high temperatures one might find on Venus. Lacking the funding to actually travel to Venus and not wanting to violate the Helsinki Declaration (ethical principles for research on human subjects), we used shlukim instead of people, and boiling water instead of Venus. The kids decorated their icy subjects, and then dressed them in spacesuits they designed from a range of materials including aluminum foil, paper towels, and inflated ziploc bags. To make it a proper experiment, we first tested a control shluk, a subject not wearing a spacesuit. The subjects were then placed in boiling water for 1 minute. Afterward, the kids opened up each shluk and measured the volume of liquid to see which one melted the least. While many an alien/astronaut costume is made out of aluminum foil, the clear winner in this experiment was the inflated ziploc bag.

General Science: 200 grams of furry love

This past week we applied some of the principles of measurement to a real life question: How can we study a kitten's growth?

Some back-story is necessary...a very cute kitten found its way into my yard, and had the good/bad fortune to be abandoned by its mom, lose its brother/sister, and fall asleep next to my automatic sprinkler. If it hadn't been quite so pathetic, maybe I would have had an easier time ignoring it. Anyway, here I am feeding a 3 week-old kitten with a bottle. Go figure.

Seemed like an excellent opportunity to learn something about cat development. The kids decided to make the follow observations: weight, eye color, tail length, as well as how much it eats and how well it walks. There were a few other characteristics, but Cucumber was getting a little tired, so we decided to give it a rest. The kids used this opportunity to learn how to use a triple beam balance (a kind of mechanical scale) and to think through how you measure something that's kind of frisky (wrap it in a towel, weigh the cat and the towel, then weigh the towel, and subtract the weight of the towel). Hopefully, Cucumber will still be around Oct 28th, next time we meet, so that the kids can do some follow-up observations. I did warn them, however, that there's a chance that Cucumber might not make it, as kittens, like all babies, do much better with their moms, plus we are looking to find him a new home, since Danny is allergic!

Anyone want a kitten?

You can have a peek at http://tinyurl.com/3vxvx4 (These are pix from my PHYSICS groups last experiment in which they "renovated" my dollhouse - see if you can find the kitty!)

Chag Sameach.

--Rebecca

Quiz: Measuring Volume

Quiz: The Candle Experiment

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