Thursday, December 31, 2009

Physics: What color is it really?

This week we did 2 mini-experiments to investigate how we perceive color. The first was with spinning color wheels. The kids compared the patterns of the discs when still to the patterns they saw when the discs were spun. The second mini-experiment involved looking at magazine pictures under the microscope and comparing the images seen with the naked eye to the colors revealed at greater magnification. Both experiments demonstrate how our brains process stimuli that our eyes receive in either in too short a time or in too small a space.

With the spinning color wheels, when we see 2 colors within a short period of time, our nervous system combines the colors. Pictures in a magazine are actually made up of patterns of tiny dots, placed closely together. Once again your brain can't process them separately and instead combines them to produce the experience of various colors. What is especially cool about the magazine pictures is that no matter what color you "see," when examined under the microscope you realize that the image is made up of just 3 colors: magenta, cyan, and yellow (aka red, blue, and yellow). By producing images that include different ratios of the primary colors, you can get just about any color.

Next time your kids paint, just give them red, blue, and yellow - make them to do the work!

Wednesday, December 23, 2009

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 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.

Monday, December 21, 2009

General Science: Iron and Sulfur

Last week we started some chemistry. The kids carried out an experiment in which they explored the properties of sulfur and iron using a microscope and a magnet. Then they combined the 2 elements and determined 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 decide!

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.

Thursday, December 3, 2009

Physics: Magnets

After completing their quizboards (hopefully 2 days later they're still intact), we started a new unit: MAGNETS

The kids investigated which materials are magnetic, compared the strengths of different magnets, learned how to turn iron nails into weak magnets, observed the effects of magnets on compasses, and used iron filings to observe magnetic fields.

Biology: 10,000 micrometers under the sea

This week the kids hunted for microorganisms in samples of pond water.

They turned up some interesting single-celled organisms, and even a worm or two. Believe me when I tell you, these 2 mm guys are pretty alarming swimming around eating algae magnified 100x!

The kids used what they learned last week to estimate the size of the different organisms. Surprisingly, we noted that the size of single-celled organisms are roughly the same size as the cheek and onion cells we looked at last week.