Wednesday, December 21, 2011

About the illustrations

Most of the illustrations at are written in JavaScript.  JavaScript must be enabled and theyshould run without trouble using the most recent version of  Firefox, Chrome, Safari, Opera, or           Internet Explorer (9 or higher).  Internet Explorer version 8 or lower will not work.

A limited number are written in the NetLogo language.  These require java and will not run on mobile devices such as phones or tablets.

Friday, November 18, 2011

Wave Interference

Anyone who as watched the surface of a swimming pool has observed wave interference. Wave interference occurs when two or more waves move through the same space at the same time. Unlike solid matter, waves move through each other. The principle of superposition describes the response of a medium being displaced by more than one wave.
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Sunday, October 16, 2011

Balancing Chemical Equations

In chemical reactions, sets
of compounds interact with each other to form new compounds. Chemists use equations to describe these interactions. Like mathematical equations, chemical equations conform to a set of rules. This allows equations to provide detailed information about a reaction.

Wednesday, September 28, 2011

Covalent Bond Energy

Eating, putting gas in a car and throwing a log on a campfire all involve adding energy to a system. In each case, the energy is added in the form of covalent bonds that hold atoms together in molecules.

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Saturday, September 10, 2011

Metric System Unit Prefixes

Similar to scientific notation, unit prefixes make very large and very small number easier to manipulate and to understand.

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Monday, September 5, 2011

Scientific Notation

Some people have a strong resistance to using scientific notation. Almost every time I teach an introductory science class, I have one or two students with good math skills who insist on doing all of their calculations in standard notation. Doing this invariably results in mistakes that lead to lost points on exams and homework.

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Saturday, June 25, 2011

Serial Dilutions II

***UPDATE- View the updated illustration at

Serial dilutions are a common part of may laboratory procedures. Background on serial dilutions, how they are performed and calculation of dilution factors are covered in a previous post.

The following illustration extends the exploration of serial dilution by following changes in the volume and concentration of a solution over three dilution steps.

Friday, June 10, 2011

Pendulum Period

Clocks with quartz movements are more accurate at keeping time than those that use pendulums. Quartz has largely replaced pendulums in modern clocks. But, in their day, pendulum clocks were profoundly important due to their ability to measure time accurately over long periods. The first pendulum clocks were produced in the mid 17th century and their impact was dramatic. Their use ushered in a new era of accurate time keeping. The reliability of pendulum clocks is based on the predictable relationship between the length of a pendulum and the time it takes the pendulum to complete one full swing.
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Tuesday, May 31, 2011

Buoyancy II

If you wanted to move a heavy rock across the bottom of a shallow pool, would it be easier to move it if the pool was empty or full of water?

The rock would be easier to move if there was water in the pool. The reason, buoyancy force.
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Tuesday, May 24, 2011

Charles' Law

Three parameters used to describe the characteristics of gases are pressure, volume and temperature. The ideal gas laws describe the behavior of gases with respect to these parameters. Boyle’s Law describes the relationship between the volume and pressure of a gas when temperature is held constant. Charles' law describes the relationship between temperature and volume when pressure is held constant.

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Tuesday, May 10, 2011

Specular vs Diffuse Reflection

Light is central to our experience of the world. Without its reflective properties, our eyes would not work. When we look at an object, the light rays entering our eyes are ones that have reflected off of the object. Our ability to determine the location and distance of the things we see stems from the fact that light rays behave in predictable ways.
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Friday, April 29, 2011

genotype phenotype probabilities

Patterns of genetic inheritance obey the laws of probability. In a monohybrid cross, where the alleles present in both parents are known, each genotype shown in a Punnett Square is equally likely to occur. Since there are four boxes in the square, every offspring produced has a one in four, or 25%, chance of having one of the genotypes shown.

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Wednesday, April 27, 2011

Note to mac users -

A recent update is causing the illustrations to run poorly on the chrome and firefox browsers. I expect a future update will resolve this issue.

For the time being you will get the best performance on a mac with safari or opera.


The definition of pH is straightforward: pH describes the concentration (or activity) of positively charged hydrogen ions (H+) in a solution. Underlying this definition is a set concepts that can be challenging to understand. The challenge comes from needing to appreciate:

Tuesday, March 29, 2011

Phase of the moon

The moon is second only to the sun as the most dynamic feature of our sky. It moves across the sky from east to west once every day and each month it goes from being invisible to the brightest object in the night sky and back to invisible again. These patterns result from the motions of the earth, moon and sun relative to each other.

Thursday, March 17, 2011

Features of a wave

A standard set of terminology is used to describe the feature of waves.
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Saturday, March 12, 2011

Boyle's Law

On Earth, naturally occurring matter exists in one of three phases: solid, liquid or gas. Matter in each phase exhibits distinct characteristics. Gases, for example, do not have a fixed volume or shape. As a result, gases respond to pressure changes by changing their volume. In other words, gases are compressible. In contrast, liquids and solids are not compressible. Their volume does not change in response to changing pressure. This is the reason air filled spaces in our ears “pop” during airplane takeoff and landings while the liquid filled spaces in our bodies do not. Boyle's Law describes this relationship between gas pressure and volume.

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Saturday, February 19, 2011

Light reflection and refraction

Light is a complex phenomena. It exhibits both wave-like and particle-like properties and its exact nature is not completely understood. This complexity makes it difficult for one model to describe all of light’s properties. As a result, different models are used to describe different aspects of light’s behavior. The electromagnetic wave theory explains light’s ability to travel through a vacuum. The light ray model, on the other hand, can describe interactions between light and matter.
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Friday, February 4, 2011

Gravitational Acceleration

We all understand that if we hold something up in the air and then let go, it will fall to the ground. Things fall because of gravity. Gravity is an attractive force between all things that have mass.  It is one of the fundamental forces of nature. Gravity causes objects with mass to accelerate towards each other. The rate of acceleration depends on the mass of the objects and their proximity. The more mass an object contains, the more it will attract other objects. The closer an object is to another the greater the attraction between them will be.
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Wednesday, February 2, 2011

Punnett Square

During sexual reproduction, a parent is equally likely to pass on to its offspring either of the two alleles it has at each genetic locus. This makes it possible to list and estimate the probability of specific genotypes being produced from the pairing of two individuals. Given two allele from each parent, four allele combinations are possible. These combinations and their probabilities can be readily visualized using a Punnett square.
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Wednesday, January 26, 2011


Why do some things float and others sink? The first thing that comes to mind for many people is that it depends on how heavy an object is. While an object's weight, or more properly its mass* does play a role, it is not the only factor. If it were, we could not explain how a giant ocean liner floats while a small pebble sinks. Mass matters, but there is more to it.
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Saturday, January 22, 2011

Serial Dilutions

***UPDATE- View the updated illustration at

Many modern biology and chemistry laboratory procedures require compounds to be mixed or dissolved in a liquid such as water.  These mixtures are called solutions.  Solutions have two components: a solute and a solvent.  Solutes are the suspended or dissolved material and the liquid is the solvent.  The amount of solute present in a particular volume of water or other solvent is called its concentration. For chemicals, common concentration units include weight/volume percent, weight percent, molarity and normality.  For biologically active compounds such as antibodies or enzymes, concentrations are often described using activity units/ml.  Concentration of bacterial and cell cultures are often reported in cells / ml or CFU (colony forming units)/ml.

Thursday, January 13, 2011

Alleles, genotype and phenotype

Genetics is the study of the organization, expression and transfer of heritable information. The ability for information to pass from generation to generation requires a mechanism. Living organisms use DNA. DNA is a chain, or polymer, of nucleic acids. Individual polymers of DNA can contain hundreds of millions of individual nucleic acids molecules. These long DNA strands are called chromosomes. Information is contained in the order of the individual nucleic acids that make up the DNA polymer. The use of DNA as the information molecule is a universal property of all life on Earth. Genetic information is read by our cellular machinery and allows our bodies to synthesize the many enzymes and proteins required for life

Friday, January 7, 2011

Types of waves

Every sound we hear, every photon of light that hits our eyes, the movement of grass blown by the wind and the regular beat of the tides are all examples of waves. They are all around us.  Visible, physical waves such as those we see when a rock is thrown into water are what many people think about when they first began to think about waves. These waves have distinct properties specific to their type but also exhibit characteristics in common with more abstract waves such as sound waves and light (electromagnetic) waves.