Saturday Science Challenge #13

Layers of the Earth

The earth has 3 basic layers--the crust, the mantle, and the core. Texts will emphasize the thinness of the crust. Making models is a wonderful way to demonstrate this, though I found my kids were particularly impressed by this demonstration.

The earth is not perfectly spherical, and the crust of the earth is irregular, so exact numbers are not really possible, but these are the ones we can use for this activity:

Radius = 6378 km
Distance to core edge = 2890 km
Distance to mantle edge = 35 km (from Wikipedia)

Take a measuring tape at least 6 m long; have someone hold it in place at the "center" of the "earth." First measure out to 2.73 m. Holding chalk and the edge of the tape together, draw a circle, or at least an arc; this first line is the edge of the core. Now bring the tape out to 6m and draw a second arc; this second line is the edge of the mantle. Ask your kids, "How thick is the crust in this model? How much longer do I extend the measuring tape to draw the crust?" Have them mark where they think the line would fall.

Answer: 3 cm

For advanced students, have them calculate the ratios. I choose to have the edge of the mantle to be 6 m, so how large is the full radius for the model? The actual distance from the center of the earth to the mantle's outer edge edge is 6378 km - 35 km = 6343 km. Now set up a ratio:

distance to outer mantle (6346) is to earth's radius (6378) as model distance to outer mantle (6 m) is to model radius (rm).

6346/6378 = 6/rm --> (6378)(6) = (6346)(rm) --> (6378)(6)/6346 = rm
rm = 6.03

You can set up a similar ratio to check the edge of the core.

Saturday Science Challenge #12

Basic Rock Identification

Around here we rarely find rocks made of a single mineral that we can identify through color, luster, streak, hardness, and cleavage, but you can classify rocks into their three basic classes: igneous, metamorphic, and sedimentary.

All you need is one hammer and goggles for everyone participating. A geologist's pick hammer is most effective though this can be done with other hammers. And you need to find a flat, hard surface on which to do the cracking.

You can play the Rock Type Game at Geology For Kids as a warm up. You can also read the classic A First Look At Rocks by Millicent Selsam, or DK e.Guides Rocks and Minerals to get an idea what to look for when classifying them.

Cracking them open, as well as wetting them, really helps to see crystals and layering. And I didn't have to ask twice if anyone wanted to do this activity. For older kids, have them try to identify the specific types in each category. They can also map the location of their rocks, and see if different locations have different predominant types. The Moh's hardness scale is helpful for this, especially the hardness of common items you can use to test your samples. For advanced students, check out the igneous rocks, metamorphic rocks, and sedimentary rocks classification pages.




These two rocks are the same specimen. The picture doesn't show how much more lustrous the inner rock is compared to the worn outer surface.







It's granite, an igneous rock.

Science Saturday Challenge #11

More About Cohesion and Adhesion

I found so many experiments about the topic I created an entire webinar with a whole series of experiments including the two from challenge #9.

You can view the webinar for free anytime.

I found a lot of my material in Super Science Concoctions--a great book to have on your homeschool shelf!

Science Saturday Challenge #10

Buckyballs and Molecular Biology

I found this article to be an interesting if unusual connection between biology and math.

Buckyball Computer Simulations Help Team Find Molecular Key To Combating HIV

ScienceDaily (2009-05-25) -- Researchers have identified specific molecules that could block the means by which HIV -- the deadly virus that causes AIDS -- spreads by taking away its ability to bind with other proteins. Computer simulations were used to test more than 100 carbon fullerene, or "buckyball," derivatives initially developed for other purposes to see if they could be used to inhibit a strain of the virus, HIV-1 PR, by attaching themselves to its binding pocket.

You can build a buckyball with Zome, or use toothpicks with marshmallows or large gummy candies (yum!) If you look carefully at the picture you will see the model combines pentagons and hexagons in a soccer ball type pattern. Each hexagon has attached to it alternating pentagons and hexagons. Here is the Zome flyer with directions from the old web site should you get stuck.

For an extension, try building a molecule with a binding pocket into which the buckyball "fits" (or at least sits in.)

To help round out your lesson you can read more interesting information about fullerene.

Science Saturday Challenge #9

Surface Tension

Water is an amazing molecule for many, many reasons, one of which is it's incredible surface tension. First read this article: Sticky Water from the Exporatorium to get an idea of why water has such adhesive abilities.

A great book about water, including surface tension, with stunning pictures is A Drop of Water by Walter Wick.

These experiments are easy to do and visually impressive, both of which make for favorite science experiments in our house!

Materials
A small bowl of water
Pepper
Liquid soap (for hands or dishes)

Procedure
Sprinkle pepper onto the surface of the water until it pretty much covers it.

Dip a clean finger into the bowl of water, and Ds#2 and Ds#3 are doing in the picture below.



Now rub your fingertip with a little of the liquid soap and dip it back into the center of the bowl.



Now try the experiment with milk and food coloring for a more dazzling display!





Soap has a polar "head" that attracts the hydrogen bonds of the water, but also has a hydrophobic "tail" that stick up at the water surface. When the water bonds to the soap the tails break up the surface tension. That makes the pepper and the food coloring scatter, and gets dirt off of surfaces!

Science Saturday Challenge #8

I successfully completed my first webinar! It has all sorts of information about homeschooling science, resources, and lots of experiments regarding static electricity. Just click on the Science Saturday logo to view the show.

Thanks to everyone who attended, and to Homeschool Connections for making this possible!

Post a comment when you try some of these yourself.

Science Saturday Challenge #7

I know, it's Sunday, but I had to work all day yesterday...

Any guesses what this is a picture of?

Science Saturday Challenge goes live!

I have thoroughly enjoyed the live webinars at Homeschool Connections, and many more have been scheduled, including mine! Science At Home: Static Electricity live webinar airs on Wednesday, May 13th at 8:30pm Eastern time. You can register here. I will be discussing homeschooling science as well as static electricity, and then demonstrating several experiments relating to the topic.

If you miss the live webinar I will post a link as the next Science Saturday Challenge so you can view it at any time.

I hope this effort will make homeschool science easier for those who are just a touch intimidated by the subject, or for those who want to break away from the textbooks and boxed curricula.

You can see all the upcoming webinars here.

Blessings,

Science Saturday Challenge #6

Tinkering With Inertia

Newton's first law of motion describes inertia: a body a rest will stay at rest, and a body in motion will stay in motion in a straight line at a constant speed unless either is acted upon by an outside force. We read about inertia in the Dynamics section of the Usborne Science Encyclopedia (pg. 122.) This is not just a linear property, but a rotational one as well.

We used Tinker Toys to explore rotational inertia. (You could also do this with clay and dowels if you want.)

Ds#3 is holding two Tinker Toy configurations that use the exact same pieces. I had the boys hold each one in the center and twist it back and forth, making the top and bottom swing back and forth like a pendulum. I asked which would be easier to swing; they thought the one with the weights at the ends would be.

They were surprised!

The farther the weight, the greater the inertia, so the harder it is to move.

Ds#2 is showing our next experiment. Here I asked the boys to try and balance this structure on their palm. They tried it with the weight closer to their palms...

...and with the weight farther away from their palm. They predicted the first position would be easier to balance.

They were surprised again!

As in the first experiment, the farther the weight, the greater the inertia, so the harder it is to move.

Next Ds#1 is demonstrating another structure that I had them balance on one finger. You see that his finger is at the center of the structure with equal weights in each end.

I asked what they thought would happen if I moved the weight in on one side. Ds#2 thought the side with the closer weight would be heavier, and Ds#1 thought the other side would be heavier. The toy fell towards the weight that was farther away. In the picture, Ds#1 shows that he had to move his finger so that it was midway between the weights, not the middle of the bar, to balance the structure.

Here gravity is acting on the mass creating a force; rotational force is called torque, which is a force exerted at a distance from the axis of rotation. The longer the arm, the greater the torque.





I then showed them how this all relates to something common: a seesaw. I asked which end of the seesaw they would rather have to lift. At first they thought the side with the closer weight, but after a moment they changed their mind.

This time they were right!

Just like the second experiment, a fulcrum is the axis of rotation, so the longer the arm the greater the gravitational torque.


We then played with the Torque and Moment of Inertia Gizmo. Torque equals the force multiplied by the distance from the fulcrum:

T = r F

Even without knowing actual values, you can see that the farther the weight is (the greater r is) then the greater the torque is. If you have to lift a weight using a fulcrum, like a seesaw or a pulley, you certainly don't want the short end of the stick!

Another example of this is when skaters spin. With their arms out, the center of mass is farther from the center and the spin is slower than when they bring their arms close to their bodies. This is also why two balls of the same mass but different size will roll down an inclined plane at different rates. The smaller ball rolls faster since less energy has to be spent to overcome the rotational inertia.

For an advanced discussion, see Fizzics Fizzle.

Science Saturday Challenge #5

This week’s challenge is inspired by the Journey North: Mystery Class in which our co-op is participating.

Seasons change because the earth rotates around the sun at a 23.5° angle. Because of that angle, the amount of daylight—photoperiod—changes from day to day, and on any given day it is different based on your latitude.

Here’s an interactive animation about the seasons at Teacher’s Domain (free registration.) Also check out The Reasons for the Seasons by Gail Gibbon or Sunshine Makes the Seasons by Franklyn M. Branley.

This week's challenge involves calculating and plotting photoperiods to demonstrate how they vary throughout the world.

Materials

• USNO web site for sunrise and sunset data (and US longitude and latitude information)
• Getty Thesaurus of Geographic Names web site for worldwide longitude and latitude information.
• A world map or globe
• Graph paper
• Colored pencils

Procedure
First create or download a photoperiod graph. The X axis is the date and the Y axis is photoperiod (from 0 to 24 hours; see here for an example. Scroll down to the Mystery Class graph.)

Figure out your own longitude and latitude by entering your U.S. town or one nearby into the USNO web site and click “Get Data” or entering your location outside the U.S. at the Getty site.

Find the longitude and latitude of 6 cities north and south of you. Spread these out from north to south as much as possible; it does not matter what longitude they are in. Find two cities east or west along the same latitude as you. You will also need to know the time zones (map here) based on Greenwich Mean Time (GMT.) Note: if you use cities in the US you can just enter the name into the USNO site and get longitude, latitude, and time zone (see below.) For cities outside the US you can use the Getty site or a map.

Use the USNO web site to find the sunrise and sunset data for your home and your chosen cities. If you are using US cities you can simply enter the city name in the top FORM A section. For cities outside the US, use the lower FORM B section by entering in the longitude, latitude, and time zone. Repeat this for several dates; I suggest doing the same day of the week for several weeks before and after the equinox, and then several weeks before and after the solstice.

Calculate the photoperiod (amount of daylight) for your nine locations and plot them on your graph, each in a different color.

Check out the slopes of the lines and consider where these locations are in relation to each other. How does moving east to west affect photoperiod? Can you tell if a location is north or south of you based on the photoperiod? How do photoperiods affect climate? How does the data change around the equinox and the solstice? There's a lot of science and math you can discuss relating to this project.

Science Saturday Challenge #4

We've been learning about properties of matter, and this week's experiment demonstrates a few of them. We read pages 10 - 19 in the Usborne Science Encyclopedia. Search for keyword "properties of matter" at your library for relevant titles.

First you'll need to make a super saturated salt solution (a.k.a. brine) by boiling 2cups of water and then adding salt in batches, stirring in between, until the salt no longer dissolves. Let it cool.

Materials:

Brine
Water (hot and cold)
Food coloring
3 small glass containers

Procedure:

Put equal amounts of brine, ice water, and hot tap water into each of the three containers (we used special plastic test tubes, the ones from which 2L bottles are made, with 2 tablespoons of liquid in each.)

Add a drop of food coloring into each at approximately the same time and watch what happens. In this video, red is hot, yellow/green is cold, and blue is brine.



The red and the yellow/green drops sank at about the same rate, but the red diffused throughout the water much faster. You can see this better with purple dye better (purple is cold, red is hot water.)

Density is mass (g) per volume (ml) or

D = m/v

For a liquid this is easy to calculate. For a solid you can figure out the volume by how much water it displaces (see pg. 17 of the encyclopedia to set this up.)

Other Resources:

Chem1 Virtual Textbook: Density and Buoyancy (advanced)

I Love Density has a complete science project on density (intermediate)

We found several Gizmos that demonstrated density. One had objects on a shelf that you could put on a scale to get weight (mass), then in a graduated cylinder to get volume. I did the calculation for the kids (they were fractions that I converted to a decimal.) You can then put the object in a liquid in which you can adjust the density. The kids were impressed when I started out with the object floating and as soon as I adjusted the fluid density to a number less than the object, the object sank.

Science Saturday Challenge #3

Expanding and contracting air has myriad applications; in our home lab we'll use it to inflate and deflate a balloon. Adding heat energy to air causes it to expand and displace cooler air, thus decreasing its density and causing it to rise. It follows that cooling the air has the opposite effect.

Materials

Plastic soda bottle

Balloon


Procedure


Fill the soda bottle with very hot tap water and let it sit for around 5 minutes to warm it up; empty the hot water.

Put the opening of the balloon over the opening of the bottle. Run the bottle, cautiously, under the hot tap water. You will see the balloon inflate a little.

Now run cold tap water over the bottle. The balloon will not only deflate, but may also be pulled into the bottle quite a bit. Run the hot water again to re-inflate the balloon.

Here are three videos demonstrating what happens:





Sometimes this is done by putting burning paper into the bottle, and instead of a balloon you use a hard boiled egg on top of a jar with just the right sized opening, sucking the egg into the jar. But this can mislead some to think that the flame is creating a vacuum by consuming the oxygen (which is replaced by other gases so no vacuum is formed.) And this version can be reversed in both directions repeatedly, making it a hit if you have multiple children that want to try it out.

Here's a PBS interactive demonstration of what is going on.

Science Saturday Challenge #2

Pressure is force applied over an area, P = F/A. The larger the area, the less the force on each unit of area. In other words, the force is "spread out" across the whole area.

Materials:

4 balloons
1 small table or other long, flat area that kids can stand on

Procedure:

Inflate the balloons about half way, tie them off, and place them on the floor.

Turn the small table over and place it on the balloons.

Holding the table stady help your children stand in the center of the table.

Ds#1 knew right away that the balloons would not pop, though he thought it had more to do with the balloons not being directly under his weight.

They noticed how the balloons changed shape; I pointed out that all 4 balloons changed because the weight (force) in the center of the table created pressure in all 4 balloons and was, in fact, divided among the balloons. Also, the balloons spread out so that more area touched the table, which decreased the pressure on any one spot.

When you do it, put the balloons under the table a bit more, otherwise the corners of the table can dig into a balloon if a child does not step directly onto the center of the table. Ds#3 stepped up with ds#1 for a total combined weight of about 100 lbs. Ds#2 had a fever and only wanted to look on.

The standard unit of Pressure is 1 pascal (Pa) = 1 Newton/m² = kg/(m· s² ), named after Blaise Pascal, who invented the hydraulic press and the syringe, among other things. The Imperial equivalent is psi, or pounds per square inch.

You can also demonstrate this using straight pins. Tape graph paper to cardboard. Stick a pin through every corner. Place an inflated balloon on the pins and a brick on top of that. Just like the bed-of-nails trick!

For more information visit:

Pressure

School for Champions

Fluid Statics calculation challenges

Science Saturday Challenge #1

Welcome to Science Saturday Challenge #1!

We'll start with something you have probably seen before: making a pH indicator.

Materials:

Red cabbage (1 head)
White vinegar (1/2 cup)
Baking soda (1 tsp)
Water
Eye dropper
Clear glass containers (at least 3)

Procedure:
Shred the cabbage. Put it in a medium pot and add water until the cabbage is covered. Bring to a boil and then let it cook for about 15 minutes. Really, I just watch it on the stove until the water turns a dark purple. Strain the mixture so you only have the liquid. Do whatever you'd like with the cabbage.

I got almost a quart of indicator from one small head of cabbage. That will keep in the fridge for awhile (my jar has been sitting there for several months.)

While the liquid is cooling, get out three glass containers (or more if you are testing more than baking soda and vinegar.) In each put:

1/2 c water + 1 tsp baking soda (stir to combine)
1/2 c water
1/2 c vinegar

In my pictures, I actually used a cup of water but the color will be more intense if you use less.

Once the indicator has cooled a bit, add 15 drops of it to each of the three containers.

The acid turns pink, the base turns blue, and the water will stay purple (red + blue = purple, acid + base = neutral liquid)

Why? Because cabbage and many other plants contain anthocyanins that change color depending on pH. These substances are what show through in colorful autumn leaves when the chlorophyll drains away. They are also why some plants will have different colors when planted in different soils.

Links for more information:

What are acids, basis, and pH? See if your acids and bases have these properties. Instead of vinegar, I actually added ascorbic acid to water. Ascorbic acid can be purchased through The Baker's Catalogue as a dough enhancer and to make sourdough bread more sour! What about slippery soap--any guesses as to its pH?

How Stuff Works: Where does the color come from in purple cabbage?

Acids and Bases: Frequently Asked Questions (advanced)

Water to Wine: the molecular basis of indicator color changes (advanced. If the chief stewart tasted these liquids, though, he would not comment to the groom that he had saved the best wine for last!)

Introducing Science Saturday

I am starting a new project here called Science Saturday. On Saturday I will post a science experiment for you to try out during the week.

Blog about your experience and leave a comment on the Science Saturday blog entry for that experiment. Include a link to your blog entry for others to see.

I hope this will encourage homeschoolers to explore more science and have a lot of fun!