Physics and Biology: Dry Ice

Dry ice is unlike the ice we know and love. It's frozen carbon dioxide, and it's called "dry" because it passes from the solid phase directly into the gas phase, skipping the liquid phase entirely, resulting in some AWESOMELY weird and funky behaviors! It's CRAZY-cold, so cold in fact, we only handled the dry ice with a towel or tweezers....NEVER with our bare hands!

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).

• made long-lasting carbon dioxide bubbles by adding dry ice to soap solution.

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

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

Corrections

My fact checker (my husband) has just informed me that all of the Sharper Image stores were closed by the end of 2008 after bankruptcy.

Take the SCIENCE IN MOTION Challenge!

Today being the last day of science, seemed like a good time to do the Science in Motion Challenge. The Science in Motion Challenge has two parts: a series of questions relating to the experiments carried out over the course of the year and a few fiendishly difficult science dares including:

• Float a paper clip in water.
• Insert a sharp pair of scissors into a soap bubble without popping it.
• Have a catch with a bubble without popping it.
• Make soap bubbles that are shapes other than spheres.

Armed with their intellect, a sense of adventure, and their lab notebooks, the kids made short work of the questions, the dares, not to mention my back yard!

It's been a great year - I really enjoyed working with your kids!
Have a wonderful summer!

Rebecca

Science Fair 2010

This year's Science Fair was a big success! Our general scientists did some excellent product testing, the physicists' inventions will no doubt be lining the shelves next year at Sharper Image, and the biologists planned and executed some fascinating projects on the human body.

Here is a quick summary of the results from the biology projects:

• Spinning with your eyes closed made you dizzier than with your eyes open.
• Doing exercise slowed down drinking capacity, more so with water than with coke.
• The effects of static electricity were observed the most in people with wavy hair.
• The right hand of righties was more sensitive to temperature than was their left.
• Boys had greater lung capacity than girls.

Our scientists had a lot more to say than just the bottom line, so please ask the kids about the challenges they faced carrying out projects with human subjects.

Kudos to all our budding young scientists as well as their supportive families and friends!

Biology: Got Milk??

This week we did one of my favorite kinds of experiments, the kind that ties in pretty much everything we've been learning about all year: chemistry, enzymes, genetics, evolution...You name it, we've got it! We started out by testing the effects of adding lactaid to milk. Using glucose strips we showed that lactaid causes the lactose in milk to break down into simpler sugars such as glucose. Lactaid is a substitute for lactase, the enzyme that mammals use to break down milk.

So far, so good....but where's the drama?! After understanding a bit about the chemistry, we looked at milk digestion in the context of human evolution. No more simulations, no more flipping coins. Instead, we took a real-life example, and one that relates to our own species. In MOST humans, as is the case in most other mammals, babies STOP producing lactase around the time they are weaned. What this means for most mammals is that drinking milk post-infancy causes stomach problems. Yet among some humans - perhaps, you know one of these mutants?! - eating milk products throughout their life is done happily with no side effects.

What made these mutations persist in certain populations and not others? The strong correlation found between populations whose ancestors hung out with cows and sheep with populations with a high frequence of lactose TOLERANT individuals suggests that the distribution of this trait is the result of some serious natural selection. Having the ability to digest milk, particularly during cold winters when others food sources were scarce gave people with this mutation a real advantage, which they in turn passed down to their kids.

So if you're one of those people who use a pint of Ben and Jerry's to take the edge off a bad day, now you know why.

Biology:The birds and the beans

Building upon what the kids already know about adaptation, we began to discuss natural selection. If individuals with one version of a trait are fitter than individuals with other versions of the trait, what happens to the distribution of this trait in the population over time?

To understand this concept, we carried out the following simulation. A lab group was given 50 red beans and 50 white beans, representing the parent generation. Each group worked in 1 of 3 different environments: the white floor, the red sidewalk, and the green (very green - oh how I love my astroturf!) grass. One kid/bird from each group would hunt for 75 beans, and then the 25 remaining survivors would reproduce, having 3 offspring, each one the same color as the parent. The kids repeated the simulation 2 more times, and then observed the long-term effects of living in a particular environment on the frequency of red and white beans in the population.

As for the results, they don't call 'em bean counters for nothin...all that counting takes a lot of time. Next week we'll review and discuss our findings.

Biology: Hunting etiquette

Which fork should you use...depends on that you're hunting!

This week we learned about adaptation. We decided to test which hand adaptation: fork, knife, or spoon would be best at hunting different types of prey such as marbles, rubber bands, and hair clips. These items were spread out on the grass, and the kids, with the help of forks, knives, or spoons went hunting. We found that spoons were best overall, but when it came to catching rubber bands, knives won hands down.

We concluded that there is no "perfect" adaptation. What works well in one environment may be less effective somewhere else.

Science Fair coming soon!

Biology: Science Fair Projects, Day 1

This week we talked about the kinds of projects the kids will be carrying out for this year's Science Fair. The theme for this group will be the human body. Over the next few weeks the kids will be choosing a question to investigate and then designing an experiment that they will carry out at the Science Fair itself, where (hopefully) there will be no shortage of available subjects.

Biology: 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.

Biology: Life in the Warsaw Ghetto

This week, biology fell out on Yom HaShoa. I decided that it would be appropriate if we discussed some issues that related both to science and to the Holocaust. We looked at some data on the typical diet of a resident of the ghetto and compared these numbers to the U.S. recommended daily allowance for proteins, fats, and carbohydrates. Then we looked at labels on different food packages to prepare a plate of food that would consist of the daily allotment for a resident of the Ghetto. Afterward we compared the population density of Raanana to that of the Warsaw Ghetto. Hopefully these two exercises helped give the kids another perspective on the suffering endured by the Jews living in the Warsaw Ghetto.

We concluded with a bit of social science: a discussion on stereotypes. The kids were given a list of sentences to complete such as, "All sephardim are...." "All Arabs are.." "All haredim are ..." The kids were given free reign to express whatever stereotypes came to mind. We put everyone's ideas on the board, and then I gave them one last sentence to complete: "All Jews are..." I suggested some of the negative stereotypes of Jews we unfortunately know too well, and as my proof gave a quick summary of the whole Madoff scandal. Many of the kids were upset, pointing out how unfair it is to judge a whole people based on the actions of one person. From there we worked backwards, reexamining many of the other stereotypes we had discussed. We left chug on a hopeful note, observing that while it is natural to group and classify people based on our experiences and knowledge, both of these things may be limited and therefore skewed. Given our unfortunate history of playing the role of the scapegoat, it is crucial for us to constantly be on our guard against harming others through negative stereotypes and discrimination.

Biology: The Genetics of Blood Types

This week we continued learning about genetics. Once again we carried out a simulation. However, there were a couple key differences from last week:

• Last week "parents" produced 1 child with a lot of different traits, and this week "parents" produced MANY kids, focusing only on a single trait.
• Last week the kids looked at made up traits, such as star- vs blast-shaped eyes, while this week they looked at a true example: ABO blood types.
• Because we had such a large sample size of offspring, we were able to compare the distribution of the different genotypes and phenotypes to what we would predict based on chance alone.
  

Biology: Chip off the old block

This week the kids carried out a simulation in which they flipped coins to see which genes they would pass on to their offspring, the offspring being different kinds of smiley faces. In this simulation, each parent was heterozygous for the 12 traits carried by smiley faces. Despite the fact the parents all shared the same genotype, the offspring displayed a wide range of variation. We discussed the importance of chance and how the number of potential combinations grows as the number of traits or more accurately, chromosomes increase.

Biology: The birds and the bees

 

This week we investigated flowers...beautiful displays of nature, so fragrant, so delicate, so easy to cut into lots of tiny pieces! Yes, this week ten flowers donated their bodies to science, so that your children could learn about the birds and the bees...literally.

The kids dissected lilies and matched each part with a description of the role it plays in making more flowers. Pollination, fertilization, ovules, and anthers, we covered it all...a comprehensive discussion of the facts of (plant) life.

Biology: DNA: Recipe for life

This week's topic was DNA, so naturally we made 3 batches of chocolate chip cookies. Confused?
Let me explain. We started by reviewing a recipe, and then the kids were divided into 3 groups, each of whom was given a slightly different version. Some of the differences involved spelling mistakes, some were missing parts of or entire words, and some had slightly different measurements. We baked cookies from each of these recipes and discussed what if any effects these different versions produced. With the recipes the kids used, the cookies all came out pretty much the same. This in itself was an interesting result. In addition, we agreed that certain typos would have yielded significantly different cookies, like say adding 1 teaspoon of flour instead of 1 cup, or adding 2 legs in place of 2 eggs.

DNA is essentially the recipe for life. How this recipe gets translated into different kinds of "cookies" (personally, I prefer oatmeal) will be our topic for the next few weeks.

FYI: I sent home each kid with a baggie of some of the unused dough, so check their bags before this evolves into an entirely different experiment.

Biology: Sensational Skin

This week we investigated a type of cell called the sensory receptor. These receptors are found in our skin and allow us to feel pressure, pain, heat, and cold. The kids made pressure probes (see photo), which were used to test 4 different areas of the body: fingertip, forearm, cheek, and calf. The idea was to GENTLY (In this particular experiment we were investigating pressure NOT pain) poke these areas with the probe, gradually decreasing the distance between the 2 toothpicks until the subject could only feel 1 prick. The area with the smallest 2-point discrimination was the area that was most sensitive and was assumed to contain the highest number of sensory receptors for pressure. The kids were surprised to find quite a great deal of variation. Subjects could distinguish 2 distinct pricks at an average of 7 cm on their fingertips, while the 2-point discrimination was much larger for the calf - as much as 30-40 cm.

Biology: What do yeast like to eat best?

Following our discussions on cell transport, we spent some time this week on cellular respiration, that's fancy talk for the breakdown of food within a cell to release energy. This process produces carbon dioxide as a byproduct.

We focused on yeast, a single-celled fungus. Some of the yeast we fed flour, some sugar, and of course some unlucky yeast got nothing at all. To get an idea of which food was eaten most heartily by each sample of yeast, we covered each bottle with a balloon. Then we sat back and watched the show. The samples of yeast fed sugar 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, and not surprisingly, the yeast fed nothing did nothing.

We related this experiment to earlier discussions comparing the size of different carbohydrates. Flour is an example of a starch, and as such is LARGE and must be broken down first before entering the cell. That takes time. Sugar, on the other hand is smaller, and can be broken down more easily.

Next week we'll be making bread and butter, so send your kids with an appetite.

Skeletons in your closet

I love chanukah! Lighting the menorah, eating latkas, and of course let's not forget the gifts. On day 6, I received the best gift ever...an animal skull! Two kids were hiking in the Carmel forest and came upon this beauty and managed to lug it home. Too good an opportunity to pass on, we skipped the usual physics and did some skeletal analysis. The kids examined a couple different skulls and mandibles and used their observations to infer a number of things about the animals including: what they ate, how they walked, and what they used more: smell or sight.
Finally they made educated guesses about the identities of the skulls. I will be consulting with my friend Efrat, the vet, to get a final verdict. Look at the 2nd picture to see if you can id the skulls.

Biology: You must be this small to ride this ride

What does the cell membrane have in common with filters, sifters, and colanders? All of the above are SEMI-PERMEABLE, meaning some substances can pass through them, while others can't.



Today we used a plastic bag to model the cell membrane. We filled the bag with corn starch solution and submerged the bag in a jar of iodine. The idea was to see which if any molecules could pass in or out of the bag. Since iodine is an indicator for starch, a color change inside or outside the bag would demonstrate which molecules had traveled through the bag.

Turns out bigger isn't always better. It's the smaller molecules, like iodine that can pass through the bag, while a large molecule like starch is going nowhere fast! We concluded by relating this to the importance of digestion. Our cells can't process large molecules like starch, so we need to break them down into smaller ones, like sugar, that can be transported more easily through the cell membrane.

Biology: Why are cells so small?

On the heels of our investigation of cells using the microscope, we addressed the question: Why are cells so small?
In order to answer it, we carried out the following experiment:
We took a whole hard-boiled egg and significantly smaller cubes of egg-white and submerged them in food- coloring. After waiting 10 minutes we took them out, cut them in half, and measured how deeply the food-coloring had penetrated. In both the whole egg and the small egg cubes, the food-coloring moved less than a millimeter in. However, the big difference was when we considered what percentage of the egg had been exposed to the food-coloring. We discussed how cells are limited in size so that they can transport food and other products in and out of the cell efficiently. We also looked at this question mathematically, considering how the surface area and volume change as the sides of a cube increase.

We looked at a few other examples where the ratio of surface area to volume matters. To name a few, cooling off hot water, root systems, and our lungs.

We concluded by making latkas.
What does this have to do with latkas? EVERYTHING!!! Like latkas, cells work best with a high surface area to volume ratio.