by: Martin Sagendorf
Most everyone knows that an equilateral prism will refract white light into its constituent colors: a spectrum ranging from red to violet. But, if one uses two prisms, there’s much more to be discovered.
Two Prisms: Four Demos
November 26, 2011
8 Comments | 
High School level, Middle School level, Physics | Tagged: light, light spectrum, PBL, phenomenon based learning, phenomenon-based science, prisms, refraction, science, Sir Isaac Newton | 
Permalink
Posted by Tami O'Connor
Thermal Conductivity: If you Want a Good Thermometer, Don’t Use Your Body
November 26, 2011by: Martin Sagendorf
An Easy Question: Which is warmer – which is cooler?
In the strictest sense, it’s a matter of energy. And we use temperature as a measure of energy level. As we all know, the greater the energy level, the higher the temperature… But, although this is absolutely true; sometimes it’s not exactly what we perceive in everyday life. When asked, we all can testify that when we touch a piece of metal we’ll say it feels cold. But is it really cold? Is it or isn’t it ‘cold’?
The Answer Is…
… very simple. If the piece of metal is at room (ambient) temperature it cannot be ‘cold’ – it must be at the same temperature as the temperature of the room.
But First:
Let’s discuss ‘perceived temperature’: this is what we ‘think’ the temperature is. It isn’t always the actual temperature (of the object we touch). Thus we enter a wonderful combination of both physics and biology. Physics describes the absolutes. Biology describes the biological reactions (interpretations) of our physical world.
It’s a matter of thermal conductivity and our nerves. Some materials are good conductors of heat (energy) and some are not. Our nerves sense only temperature – so if thermal energy is rapidly removed from the tissues surrounding our nerve endings (like at our finger tips), our nerves sense that the temperature ‘they feel’ is cooler – e.g. the material is removing thermal energy from the body tissue surrounding the nerve ends at a rate faster than our body can re-supply energy to the tissues – thus our nerves sense this as ‘cooler’.
Now:
A truly illustrative and memorable way to present the question: Read the rest of this entry »
Leave a Comment » | Biology, Elementary level, High School level, Middle School level, Physics | Tagged: conductors, discrepant event, heat energy, insulators, perceived temperature | Permalink
Posted by Tami O'Connor
Ghost Eyeballs | Growing Spheres
October 14, 2011
by: Norman Barstow
Educational Innovations’ Growing Spheres can be used to add a note of ‘horror’ to your classroom or home Halloween experience. Once fully expanded, Growing Spheres have an index of refraction almost identical to that of water. This means that when the Growing Spheres are placed in water, they are nearly invisible.
3 Comments | Chemistry, Elementary level, High School level, Middle School level | Tagged: ghost eyeballs, halloween fun, homeschool, index of refraction, parent friendly, polyacrylamide, polymer crystals | Permalink
Posted by Tami O'Connor
Make Your Own Clock Faces
October 10, 2011by: Martin Sagendorf
A Definition:
Clocks measure time – it can be a continuous measure of events passing or the measure of the interval between two events.
Of Hours:
After years of evolution, our modern clocks now divide the day into 24 equal length hours. And, as we know, there are two systems in use today: Americans use the “double-twelve” system while the rest of the world uses the 24 hour system.
As An Aside:
The word “hour’ comes from the Latin and Greek words meaning season, or time of day. A “minute” from the medieval Latin pars minuta prima (first minute or small part), originally described the one-sixtieth of a unit in the Babylonian system of sexagesimal fractions. And “second” from partes minutae secundae, was a further subdivision on the base of sixty – i.e. “a second minute”. (ref. Pg. 42 The Discoverers by Daniel J. Boorstin)
The “Double-Twelve” Clock Face:
Has 12 at the top – probably because at noon the sun is at its highest point in the sky.
But…
We can make a clock with 12 o’clock anywhere we wish and the clock will still work just fine. Read the rest of this entry »
2 Comments | Chemistry, College level, Elementary level, High School level, Middle School level, Physics | Tagged: clock making, homeschool, interesting clock, parent friendly | Permalink
Posted by Tami O'Connor
The Law of Dulong and Petit
September 3, 2011
by: Dr. Jean Oostens
Atoms were proposed in antiquity without any experimental evidence by Democritus, a Philosopher. This must have been a problem for Newton and Leibnitz who posited that there was always a mean of considering smaller and smaller intervals of space to calculate the “instantaneous velocity”.
The introduction of the precision balance in chemistry by Lavoisier paved the way for Dalton to formulate his laws on the “definite and multiple proportions” governing chemical reactions. This supported the atomic theory, without giving it general acceptance.
Specific heat was defined as the quantity of heat needed to increase one gram of a substance by one degree. There was no definite pattern when specific heats of various substances were compared. Until two French scientists in 1819 calculated specific heat by atomic mass, forming the Law of Dulong and Petit. There appeared a number of cases where the results were quite similar: about 6 calorie per mole. This was equivalent to stating that any atom is as good as any other to store heat! This was a small step towards acceptance of the existence of atoms. An explanation for this, and the reason for the exceptions, had to wait the early 20th century explanation by Albert Einstein. By that time, atoms had gained wide acceptance from the work of Rutherford, and soon by Bohr.
Lesson on the Law of Dulong and Petit:
You are given several chunks of metal, each containing 0.6 * 1024 atoms (i.e. one mole) of one element. How will each of those samples, when dropped in a standard quantity of hot water (typically 200 mL and 70 C) affect the temperature?
Step 1. Use a good balance (at least 0.1 gm resolution) to determine which element you are dealing with. If possible confirm your identification with an additional cue. Read the rest of this entry »
1 Comment | Chemistry, College level, experiments, High School level, Physics | Tagged: Chemistry, Dulong and Petit Law, metals, mole, specific heat | Permalink
Posted by Tami O'Connor