Milk Snake Eggs (will hatch in another week or so)

A Physics Digest—Part 6: Light

Last time I described how the electromagnetic spectrum spans a huge frequency range—from radio waves to gamma rays, a factor of a trillion or so. Only the tiniest part (one billionth) of that range, in the very middle, is the light visible to our eyes. Everything we see is confined to that incredibly narrow strip—it’s our constricted view of life.

One property of visible light that’s crucial to our sense of sight is reflection. If ordinary objects didn’t reflect the sun’s light, we’d not see them (sort of like the Klingon cloaking device on Star Trek). Ordinary things don’t emit light on their own, so we need reflections from the sun or other light source to know they’re there.

While light waves reflect from opaque objects, they penetrate materials like glass and water—wherein they move more slowly. When a light wave is forced to slow down upon entering a transparent medium, it will bend or refract. If you look at a spoon sitting in a glass of water, it appears bent. Refraction is also used in eyeglasses and telescopes, to focus rays of light.

In air or in a vacuum all the colors (all frequencies) of light move at the same speed, but in glass the low frequencies (reds) move faster than high frequencies (blues). Thus light can get separated into its constituent colors upon entering a glass prism and becoming refracted. The same process creates a rainbow; each raindrop acts like a tiny prism.

Sunlight appears white because it contains all colors mixed together. (Actually, it’s a little yellowish, since the sun emits a little more light energy at yellow wavelengths.) So how does a red balloon appear red, when only “white” sunlight strikes it? The balloon absorbs all light frequencies other than red; only the red wavelengths are reflected. If all the colors get absorbed, it’s a black balloon.

Why is the sky blue? White sunlight enters our atmosphere and some of it gets scattered by particles in the air. Blue (high) frequencies get scattered more than any other color, so the sky gets filled with “blue rays” of light. Why is the sunset red? When overhead, the sun is whitish-yellow, but as it sets (or rises) its rays must then travel a longer path through the atmosphere to reach our eyes. The lowest frequencies (reds) are the least scattered color. So red rays penetrate the thick atmosphere best and are the ones we see.

Our eyes’ retinas contain light sensing rods and cones. Cones (at the center) respond to color and also give us acute central vision. Rods (surrounding the center) do not sense color and give us less detail in peripheral vision. They can “see” at light levels a hundredth of what cones need, however, so in dim light we can still see, but with fewer details and no color.

Two or more overlapping electromagnetic light waves can either reinforce or interfere with each other. Scientists have learned much about light—its speed, its color composition, and the nature of the media it’s traversing—by studying the reinforcement and interference patterns that the waves make.

Although we see most objects by the sunlight they reflect, a few things emit light themselves. Fireflies do it beautifully. An incandescent light does it by getting heated up so much that it glows. When some types of gas are zapped by electrical energy, the electrons in their atoms are bumped up to a higher energy state. These excited electrons quickly drop back to their usual lower energy level, and emit photons of light. This is how neon and fluorescent lamps glow.

The electrons in some elements don’t immediately jump back down to a lower energy state right away, but hold on for a while. This is phosphorescence. And when the emitted light waves are all in step with each other (reinforcing each other) we get the intense beam of a laser.

Every element emits its own unique signature of photons (i.e., color of light) when excited electrically. Astronomers use these signatures to determine what elements are present in various stars, so we don’t have to travel there to sample them directly.

Poke Milkweed

A Physics Digest—Part 5: Electricity and Magnetism

Our world is filled with electrical devices—in fact, all matter is electrical in nature. Every atom contains negatively-charged electrons orbiting a positive nucleus of protons. Positives and negatives attract each other. This is what holds an atom together. So what keeps all those mutually repulsive protons squeezed into an atom’s nucleus? The strong nuclear force—which we’ll get to in a later entry.

Some materials can be charged with static electricity by rubbing them. Shuffle across a rug in winter (when the humidity is low) and touch a door handle—watch the spark. Rub a balloon on your shirt and stick it to a wall: electrical attraction.

Some materials are good conductors of electricity; e.g., metals, which also conduct heat well. Other materials are poor conductors; e.g., rubber, so we coat electrical wires with rubber, in order to be able to handle them without a shock.

When electrical charges move along a wire, we have an electrical current; which can be thought of as analogous to water flowing through a hose. Voltage corresponds to pressure in the hose, and a battery is like the pump that pushes the water.

We can have direct current (DC), in which all the electric charge flows in one direction, or alternating current (AC), in which the charge reverses direction (60 times a second for the electric power coming into our houses). Voltage can do work as it pushes current, such as when it turns an electric motor. We measure the work that is done by the power it produces—in watts.

The discovery of magnetism predated our grasp of electricity by a few millennia. The Greeks played with magnetic stones they found. Material gets magnetized when clusters of atoms line up, military style. That lineup creates directional properties, for which we assign a north and a south pole to the magnet. Where did we get that convention? The Earth’s iron core creates a magnetic field that points towards the north and south poles. A magnetized compass needle aligns itself with this field. Some birds have a built-in magnetic compass to navigate themselves via Earth’s magnetic field.

A wonderful property of matter is that electricity and magnetism are coupled. When electricity flows in a wire, it sets up a magnetic field around it. Conversely, if you move a wire through a magnetic field, it causes an electric current to flow in the wire. Better yet, if you move a wire carrying current through a magnetic field a force on the wire can be felt. This is the essence of electric motors. That force can do work rotating a motor, maybe even moving an electric car.

One more fascinating property of electricity and magnetism is that their interaction creates electromagnetic radiation. If we vibrate a wire that’s carrying an electric current back and forth, we cause the wire’s surrounding magnetic field to similarly vibrate. This interaction sends out an electromagnetic wave, which happens to travel at the speed of light. In fact, these waves are light! They can move through the vacuum of space, like the heat radiation we saw earlier.

How fast we wave the wire back and forth determines the frequency of the electromagnetic wave. At low frequencies we get radio and microwaves (the latter can cook food). At mid frequencies we get infrared, visible light, and ultraviolet radiation. At high frequencies we get X-rays and gamma rays. These are all the same kind of waves, all moving at the speed of light.

On to more light next time.

Bald-faced Hornet Nest (We're keeping our distance)

A Physics Digest—Part 4: Sound

Sound begins when something vibrates—sending a sound wave through the air. The ear then gets stimulated and electrical impulses reach the brain. So does a tree make a sound when it falls? By this definition, only if an ear and a brain are present to sense the air’s vibrations.

While light and heat waves can travel through a vacuum, sound waves need a medium—a solid, liquid, or gas. (So a tree falling in outer space would be silent.) Sound waves travel at different speeds in different materials (they move faster in solids than air). A sound wave is transmitted within a medium when something makes a part of that medium vibrate. That part jostles neighboring parts, and the disturbance moves along—just like heat. Throw a stone into a pond and watch the circular vibration waves move outward. While the disturbance (energy) flows along, the material itself doesn’t. Watch a cork on the surface of the water bob up and down and notice that the cork doesn’t move outward with the wave.

The rate of vibration of sound is defined as its frequency. Our ears can register frequencies as low as 20 vibrations per second (Hertz), up to as high as 20,000 Hertz (although my aging ears quit at about 12,000). Sound waves transmit energy, which is often measured as loudness. Our remarkable ear can sense loudness levels of greater than a range of a factor of a trillion, so we squeeze that down into a workable logarithmic range of about 120 decibels.

Sound can become particularly attractive when we talk about music—although it can be very subjective. One person’s music is another’s noise. As a less subjective evaluation, we’d pretty much all of us define a jet engine as making a lot of noise.

Qualities of musical sounds that describe their properties are pitch (the same as frequency) and timbre. When a musical instrument makes a sound, it is composed of a fundamental tone (the basic pitch) and various overtones, which are whole-number multiples of the fundamental. The particular mix of these multiple tones defines the timbre of the instrument—its unique sound quality.

Musical instruments make sounds in three ways: by vibrating strings, vibrating air columns (horns and woodwinds) and vibrating surfaces (cymbals and drums). All of these sounds are simulated in a stereo system when an electrical signal causes a speaker surface to vibrate.

Our ear loves regular mathematical relationships between musical pitches. When the pitch of one sound is twice that of another, we hear an octave. When the ratios of pitches are whole number fractions—like 5/4 and 4/3—we hear musical intervals of a third and a fourth, respectively. That’s harmony!

Sycamore Tussock Moth Caterpillar (Halysidota harrisii)

Sycamore Tussock Moth Caterpillar (Halysidota harrisii)

A Physics Digest—Part 3: Heat

All matter we’re familiar with possesses some amount of heat, which means its atoms and molecules constantly jiggle about. The hotter something is, the greater the jiggle. Atoms in a solid can jiggle only so much, before they break loose and form a liquid. Heat it some more and atoms jiggle even more and spread out into a gas.

Temperature: it’s a measure of the thermal energy of something—it’s a way to quantify of the amount of kinetic (jiggling) energy of the atoms and molecules. The calorie: it’s a measure of the amount of heat energy it takes to raise the temperature of a body. We convert food calories (heat energy) into the energy of walking or doing the work of lifting things (like our bodies off the couch).

Heat always moves from hotter to colder bodies (cold doesn’t move); and does so in three ways. (1) Conduction—warmer jiggling atoms in a solid pass their jiggle on down the line. Good conductors (metals) pass it on faster than insulators. (2) Convection—hotter molecules and atoms in a liquid or gas move to cooler places and warm them. (3) Radiation—heat energy gets transferred by electromagnetic waves (we’ll look at them later).

Now comes the hard part: thermodynamics. No undergraduate class gave me more grief than thermo. Thermodynamics is the study of heat and how it’s transformed into mechanical energy. It’s a macroscopic discipline—not caring about the jiggling of individual atoms, just the net impact of what they do in concert. Thermodynamics is the basic study of how engines transform heat into useful energy: your car, a refrigerator, a nuclear power plant.

One of the basic concepts in thermodynamics is the temperature of absolute zero (there is no maximum temperature). Energy can always be extracted from any warm body; but when we get that body down to absolute zero, there is no energy at all (no more jiggle). Thus it’s the absolute ground floor for all heat calculations.

Similar to Newton’s discoveries for forces, thermodynamicists have discovered two basic laws. The First Law of Thermodynamics describes the conservation of energy—that it can neither be created nor destroyed, just transformed from one type into another. Thus when we add heat to a system we can then transform it into various forms of energy, knowing we can account for every portion without something mysteriously disappearing.

The Second Law of Thermodynamics tells us that heat always flows from hot to cold locations—always downhill. Thus energy always dissipates, is always deteriorating into less useful forms; eventually into waste heat. Entropy is a measure of this disorder.

American Lady, wing bottoms

American Lady, wing tops

A Physics Digest—Part 2: Properties of Matter

Matter is what physics is all about—in contrast to mind and spirit (which are the province of other specialties). All matter is composed of identical, infinitesimal building blocks: quarks and leptons. They come together to form a little bit bigger building blocks we call electrons, protons, and neutrons—which then form atoms. Everything in this wide universe is made up of only about a hundred kinds of atoms, arranged in endless possibilities. It’s all in how it’s assembled.

Of those 100 kinds of atoms, only about a dozen are used in the common stuff we see every day (most commonly carbon). When the universe was very young it consisted almost exclusively of hydrogen atoms—which are the simplest: one proton, one electron. Gradually, over time, other kinds of atoms got manufactured in the explosive belly of stars. We are stardust!

Atoms are ageless—once created, they’re pretty much forever. They move through us continually. Oxygen atoms you inhale today were once inhaled by Jesus (or maybe a gnat on his neck). Atoms are mostly nothing—each one is the tiniest speck of a nucleus, surrounded by vast space. We’re mostly nothing!

Matter comes in three basic flavors: solids, liquids, and gases. When atoms combine into molecules and get firmly locked into a structure, we call it a solid. When the molecules are ordered in a precise fashion, we call it a crystal—like the sodium chloride molecules in salt. An electrical attraction between atoms and molecules in a solid binds them tightly together. Solids possess density (how much mass is squeezed into a given volume)—thus the iron atoms in steel are heavier and packed together more tightly than the carbon atoms in wood.

Some solids also possess elasticity: the ability to distort under force and then bounce back, once the force is removed. But inelastic solids, like a lump of clay, get bent and stay bent.

In liquids the molecules are not fixed—there’s less electrical attraction between them—so they slide over each other and can assume the shape of the container they’re in. Analogous to the weight of a solid is pressure in a liquid: the force that a liquid exerts on the surface that contains it. Liquids also possess density; thus less dense oil will float on denser water. Useful properties of a liquid are hydraulics (a property of pressure) and capillarity (which allows trees to suck up water).

The third flavor of matter is gas—in which the molecules are even freer from each other. A gas will expand to fill its container, as its molecules spread out. But gas does have weight (also expressed as pressure), so we experience atmospheric pressure, when all that air piles up above us. Gas can also float less dense objects, such as air floating a helium-filled balloon. Gases can exert forces: hold your hand out of a moving car’s window and you’ll feel it.

The force of gas also holds up an airplane—which is far denser than air. How? Air flowing over the curved top of a wing must travel farther (and thus faster) than that across the flat bottom of the wing. Bernoulli showed us that the faster air moves, the lower is its pressure; so more pressure (force) is applied to the bottom of the wing, lifting it—along with the solid airplane attached to it.

Tiger Bee Fly (parasite of carpenter bee)

A Physics Digest—Part 1: Motion

A discussion of the mechanics (the physics) of motion is pretty much a look at the early history of European physics—as it morphed from a general topic of natural philosophy into a precise science of physics. It began, however, with the Greeks. (What doesn’t, in Western culture?) A few of the Greek natural philosophers arrived at very accurate understandings of motion, while others conducted “thought experiments”—never testing out their ideas—that were shaky at best. Some of their misinterpretations hung around for nearly 2000 years, before they were fixed.

One of the key fixers was Galileo, who became one of the first natural philosophers to put his ideas to test—in 16th century Italy. He introduced the concept of inertia: that a body at rest wants to stay inactive until something budges it. More importantly, Galileo also showed us that inertia means that a moving body wants to keep in motion (at a constant speed), until something either slows it down or accelerates it. His insights paved the way for the understanding of the motion of projectiles and satellites. The moon is a satellite of Earth, as we are a satellite of the sun.

These Galilean insights opened the door for Isaac Newton to formulate his three laws of forces. He understood that a force was the thing that overcame the inertia of a body—getting it moving or slowing it down. He also discovered that every body has mass: an inherent quality that provides a measure of its inertia. Massive things have a lot of inertia. It takes more force to push them. So what is weight? It’s just a measure of how much force Earth’s gravity pulls on a body.

Newton was also the first person to grasp the essence of gravity. As I wrote in an earlier posting (5/26/09), Kepler got some hunches about gravity—believing it to be some kind of force that the sun exerts on planets—but never quite got the full picture. Newton did. The popular image has him getting his inspiration when an apple (being pulled down by gravitational force) hit him on the head. Whatever really happened, Newton understood that gravity is the force that pulls the apple and keeps us circling the sun. He came up with an elegant equation to describe it.

August is a Berry Good Time

A Physics Digest

Over two millennia ago the Greeks founded the study of philosophy—fundamentally defined as the love or pursuit of wisdom. It is the search for underlying causes and principles of reality. That love of wisdom soon divided itself into two fields of study: (1) discerning the truth of existence as we humans perceive it (what is today’s philosophy) and (2) seeking to understand the reality of the universe, independent of human perception (i.e., not filtered through human senses). The latter branch of philosophy became known as natural philosophy: the study of natural phenomenon. Today we call it physics—the most basic of the modern sciences. (Other physical sciences: chemistry and astronomy. Life sciences: biology, botany, and zoology.)

Some 25 years ago I had the opportunity of teaching physics at the local college. Physics had been one of my stronger subjects when I was in school, so I looked forward to passing on the insights of this most basic of sciences. I love physics, but I also know that it intimidates most people. It needn’t. It scares people mostly because it’s usually taught by constantly throwing equations at students and then making them mindlessly crank out solutions, with minimal understanding of the concepts. So I made it my mission to get students excited about physics—rather than becoming frightened of it. My success was uneven, but I had fun at it for a few years.

I love physics because it is so basic. It’s the foundation of all other sciences. It’s also the most elegant science; the most graceful and simple. Now, I never used the word simple with students who considered physics to be devilishly hard, but it is simple, in the manner of being unadorned. Physics shows us the “how” of this universe—not necessarily the “why”. That’s the province of metaphysics.

To me, physics is the study of nature’s fundamental behavior—often expressed in elegant equations. I think it is beautiful and wonderful that the natural world behaves in such a straightforward, dependable, and honest manner. God doesn’t play capricious games with creation; the basic truths and beauty are constant and await anyone who puts attention to them.

I believe that as we develop an understanding of our world, we cannot have anything other than awe and a reverential attitude towards it all. The loveliness and harmony of nature are exquisitely expressed in the so-called laws of physics. Physicists do not create these laws; they are nature’s rules of conduct. They ain’t just equations; they’re sacred rules.

Over the next several posts I will attempt to provide a very brief digest of a year’s physics course. It won’t provide anyone a detailed comprehension of natural philosophy, but it will touch most of the bases of what the study of physics encompasses: the basic structure of this divine creation.

Robber Fly

Cardinal Window Woes

While our homestead may host a small flock of chickadees and titmice, we’ve never had more than one mating pair of cardinals. The resident male cardinal has consistently been intolerant of having any other guy of his species hang around. For a few years after we moved here the male was devilishly irritating; he kept attacking his own image in our windows, assuming it was his dreaded foe. Some days he’d land on a sill and bash away at himself for an hour or two. When that hour or two was at five in the morning, I was ready to throttle him.

I began to think that he’d addled his brain, turning it to mush, in his compulsive assaults that seemed to grow ever longer. I read with great trepidation that cardinals could live more than 20 years. That longevity, however, was achieved by a bird in captivity. Wild songbirds are lucky to live to an age of five. It made me wonder how old this guy was. How many more years would he pester us? Would he break the wild record and live with us for many more years? And would his replacement just carry on the tradition? I found my fondness for cardinals waning.

I tried taping pictures of hawks, owls, and other birds of prey to the inside of the windows, in a futile attempt to intimidate him. The fierce photos didn’t faze him. He pecked in their faces. I finally hit on the idea of tacking strips of chicken wire over some windows—just to keep him from reaching the glass. After attacking the wire a few times, he finally gave up.

A related problem had been disturbing us during that period: birds flying headlong into the windows and either becoming stunned or killed by breaking their neck. When a bird flies toward a window it sees the reflection of the sky behind it, not realizing it’s about to meet hard glass. We coddled a few birds until they regained consciousness, but it was heartbreaking to hold a bird whose life ebbed away.

After several failed experiments (like my earlier taping up of raptor photos) I hit upon an idea: fasten small tree branches to the outside of the window, so a bird perceives a tree, not open sky. It even allowed me to remove the ugly chicken wire, as the cardinal had by now apparently changed his ways. Window collisions dropped drastically, and cardinal peckings continued to be lacking.

Mom and pop cardinal even eventually became adapted to our presence—if not exactly tame. Once too shy to come to the feeder, they’ve now grown to be regular customers. They are usually the first at dawn and the last at dusk. It’s quite a sight, when light levels are diminishing, to see the brilliant red of the male fly to the feeder and sit there for several minutes, cracking sunflower seeds and spitting out the shells.

Just recently I was treated to the sight of the father feeding one of his fledged offspring, who’d scarcely acquired flying skills. Dad would pick up a seed, discard the shell, and fly to a tree. The youngster would immediately and awkwardly fly to him and get its reward: the seed stuffed into his gaping bill. The father always flew to a different spot, making his baby fly to him. It seemed to be both feeding and flying practice.

A couple of days later we heard a crash against the window and we once again sickeningly looked at each other, knowing this was a hard impact. I went out to find an immature cardinal lying on the ground, bleeding from its bill, quickly expiring. I winced yet one more time at a death that we had caused, while in vain trying to prevent it. Casing the situation out, I guessed that the inexperienced bird had tried to aim between two twigs on the branch that was tacked to the window, but failed.

I was greatly relieved later that day, when I saw the father feeding another of his offspring. I apologized to him for placing a window in his baby’s way and wished him success in his current parental investment. Could he also pass on the lesson of avoiding those branches on the windows?

Phoebes Just Hatched