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.

NatGeo's Known Universe

Known Universe premiered this month on the National Geographic Channel. If you missed it, I suggest you find out when it will air again.

It's a three part series: The Biggest and the Smallest, The Fastest, and The Most Explosive. It covers topics like the time-space continuum, the Big Bang, black holes, meterorites, gravity, and much more. It can be intense at times with some discussion of the likelihood of future dooms-day scenarios, but mostly it is filled with lots of great physics and astronomy presented in a clear and engaging program.

Living Book (and publisher): Little Skink's Tail

Little Skink is a lizard with a brilliant blue tale that falls off to protect her. She then imagines herself with the tail of other forest creatures until she is surprised by finding her own tail has regrown.

The book is geared towards younger children and is a lovely nature story, not just a telling of facts. The illustrations of the five-line skink with various tales are beautiful and amusing. The book even has mapping and matching activities in the back. According to the book flap, this is Janet Halfmann's 28th book so I am very interested in her other writings.

The book is published by Sylvan Dell Publishing, a company dedicated exclusively to math and science literature. Their offerings are mostly on Nature, but with several other topics as well. Still, their nature books alone are well worth adding to your "must read" list for living science. The editor and co-owner homeschooled her children, and they even ran a contest for homeschool student last year. What a perfect Living Science publishing house!

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.

Skeleton model

We finished our skeleton model this week, as well as the corresponding chapter in Blood and Guts.

In the picture, the models are being held onto a magnetic bar by magnets embedded into color plastic spheres that I placed in the eye sockets.

My kids also taped their thumbs to their palms and tried to do their daily activities that way. It lasted 30 minutes.