Tuesday, November 30, 2010

Magnets and Declination

In The Joy of Science, Lesson 11: Magnetism and Static Electricity, Robert Hazen explains that the Earth is itself a giant magnet. In the Northern Hemisphere, the north end of a compass will point down towards the magnetic North Pole. He described an experiment by Robert Norman in his book The Newe Attractive which showed the declination by floating a magnetized needle in a piece of cork in a container of water. By shaving away the cork, Norman got the needle to float below the water's surface so that it's dip toward the Pole could be seen.

We tried to recreate Norman's experiment from Hazen's description using a needle and a straightened paper clip as the magnetic pointers, and real and artificial cork and pieces of a Styrofoam cup as the floatation device.We did get the needle to point on a north-south axis. But it was hard to tell if the needle dipped, because the angle would change depending on where the cork was.

There's another description of Norman's experiment at Practical Physics. And Safe and Simple Electrical Experiments (viewable through Google Books) gives some alternate ways of observing the declination of the needle. You can find the magnetic declination for your position at NOAA's Geophysical Data Center.

Wednesday, November 17, 2010

First Law of Thermodynamics: Heating Sand by Shaking It

The first law of thermodynamics says that the total amount of energy in a closed system remains constant. There are many different forms of energy, and energy can shift from one form to another. So the total amount of energy in a closed system is the sum of all the different forms of energy added together.

To test this principle, we measured the temperature of sand in a Styrofoam cup.This experiment was suggested by Professor Robert Hazen in his video course The Joy of Science. In his video, he used a jar of sand. However, we decided to use insulated cups so we didn't have to open it to measure the heat. We first measured the sand's temperature, then we sealed the cup, shook it for about five minutes, and measured the sand again. The sand's temperature actually changed from 65 degrees Fahrenheit to 68 in just the five or so minutes we shook it.


2 disposable insulated cups (we used Styrofoam)
masking tape
and a food thermometer (the kind with a sharp metal probe.)

  1. Pour the sand into one of the cups until it is about three-quarters full. 
  2. Measure the temperature of the sand.
  3. Place the empty cup on top of the cup with the sand on it. Tape them together.
  4. Shake for five minutes.
  5. Poke the thermometer's probe though the top of one of the cups. Measure the temperature again. You should see the temperature go up a few degrees.
What Happened:

Shaking the sand is a form of kinetic energy. The friction of the sand particles rubbing against each other converts the kinetic energy to heat energy. Some of the kinetic energy also converts into the energy of sound waves, which you can hear while you shake the sand.

Wednesday, November 3, 2010

The Joy of Science

Image: SmartFlix
We have been watching Robert Hazen's lecture series The Joy of Science for about a month and a half, and we are really enjoying it. A six-DVD set from The Teaching Company, The Joy of Science consists of 60 half-hour lectures using the history of science as a way to organize the major connecting principles.

Although low-tech in production values (one reviewer found it annoying that Hazen talks to an imaginary studio audience and not the camera), the series breaks down important scientific concepts and developments into small chunks that are easy to understand.

Along the way, Hazen does little demonstrations that can be used as the basis for at-home experiments with kids. We've done a couple of these already, and my plan is to post about them so others using this course will have the activities at hand, ready to go when they get to the related episode.

Just a note: The Joy of Science, like most Teaching Company courses, is not cheap. As I write, they are on sale for $149.95, down from a regular $624.95! I was lucky enough to find a library in our lending system that was willing to send me each DVD set one at a time and keep it for an extended period. (The librarian admitted that no homeschoolers in her area were interested in it because it included evolution.) We were luckier still to discover that a family in our homeschool group owned the set and were willing to lend it to us for as long as we needed.