Making a (very small) Virtue of Necessity

As I climbed to the third-floor classroom yesterday, I got to wondering how much energy I was burning.  I was predisposed to think of stair-climbing in term of calories (rather than, say, heart health) because I have put on a few pounds lately.  (Okay--more than a few.) 

This could be quite complicated as a biology question, but in terms of physics, it can be done--very roughly but adequately--in five minutes on the back of an envelope.  In fact, with some simplification it can be done in your head.

The first thing to realize is that height is a kind of energy (potential energy).  Consider a car about to roll down a hill in neutral: when that car steam-rolls you at the bottom, you will have experienced that potential energy converted into the form of motion (kinetic) energy.  By the same token, energy is "stored" in an object as it is raised to a height.  That means the energy I burn in walking up the stairs is roughly equal to the amount I gain in potential energy in going up two floors. 

A moment's thought will convince you that potential energy depends on both the mass of the object, and how high it is.  (An anvil falling on your head will affect you differently than a marble from the same height.)  It also depends on the "acceleration of gravity" (symbolized "g"), which describes how quickly a falling object on earth accelerates, and is equal to 9.8m/s².  (This translates: a falling object increases its speed by 9.8 meters per second for each second that it falls.)  The actual equation for potential energy (E_p) is:

                                           E_p=mgh               

--where "m" is mass in kilograms, and "h" is height in meters.  (E_p is in Joules; a Joule is the amount of energy needed to accelerate a 1kilogram object by 1 meter per second every second.)

I'm guessing the floors of the school to be 4 meters apart, so 8m total height.  Taking g to be nearly 10, and my mass to be almost exactly 100kg, we have:

                               100kgX10m/s2X8m=8000J

Sounds like I'm burning a lot of energy on my climb!  Now to turn that into a more familiar unit: a calorie is four-point-something Joules--call it four even for simplicity.  Now I have burned about 200 calories on my climb.  But wait! in one of the stupider coincidences in science, there are two kinds of calories**: the regular sort used by physics, and the Calorie (big "C") used in considering food.  A Calorie is equal to 1000 calories.  So my climb actually only burned about 2 Calories. 

Bummer.

According to the sugar bag in my pantry, a teaspoon of sugar--not much more than I put in my coffee--has 15 Calories.  So every time I walk up to the third floor, I burn through only a few sips of my morning brew.**

Deep funk.

I suppose the take-home lesson is one I already knew: you can't exercise yourself into weight loss (unless maybe you're the athletic type, in which case you probably don't have to); you have to control your eating.  (Yes, there's more to it, but it's still unavoidable.)  Probably I should stop making hermit cookies, full of deadly brown sugar, molasses and butter.  From the scientific point of view, it's pretty cool (and scary) how much energy food contains. 

*Another definition: a calorie (small c) is the amount of energy needed to warm one gram of water by one degree Celsius.  Therefore a Calorie can warm a whole kilogram by the same one degree.


**Okay, so it isn't really that simple: since I am assuming our bodies are 100% efficient at converting chemical (food) energy--via muscles, joints, etc.--into potential energy.  What if our bodies were only 25% efficient? or 15%?  I still don't burn that whole cup of coffee!

Misconceptions of the Seasons

 

From Wikimedia, via EarthSky.org

I was collapsing a cereal box last Wednesday for recycling when I noticed an explanation of the seasons on the back.  It had been quite a while since I'd noticed "educational packaging" of this sort, and here it was on a box of Shaws store brand (Essential Everyday) cold cereal. 

Does anyone pay attention to these things?  In this case I hope not.  Alas, Shaws disappointed: they got the importance of the axial tilt, but explained that the northern hemisphere warms in summer because it is "closer to the sun" than the southern hemisphere.  Out of a total earth-sun distance of 93,000,000 miles, that's only a difference of 0.0086% from one side of the earth to the other.  And that's the maximum possible distance; the actual difference between distances to the poles would be less than a tenth of that.

Here's a better explanation. 

The rest of the article--which isn't really about the seasons--interests me more.  It first explains the slow wobble in earth's axis, and its consequences.  Then it mentions seasons elsewhere in the solar system.  Finally it discusses the common misconception that our changing distance from the sun causes seasons. 

Three comments on these.

First, Uranus has extreme seasons because its axis is tipped nearly 90 degrees, so that its poles alternately face the sun directly--well and good; but what does it mean that Venus (with no seasons) has a tilt of 177 degrees?  Although Venus' axis is nearly upright, we know it was tipped completely over early in its history because it rotates in a direction opposite that of Earth and other planets.  That is, Earth, Mars, etc., both rotate and revolve in the same direction (counterclockwise viewed from above the north pole), while Venus rotates clockwise! 

Second, although Mars has a similar tilt to earth, unlike Earth its seasons really are caused by changing distance from the sun!  The reason is Mars' orbit is less circular than ours, a longer ellipse, so that the greater difference in distance overwhelms any seasonality related to axial tilt. 

Finally, two facts help refute the idea that earth's seasons are related to its distance from the sun: (1) the seasons are opposite in the northern and southern hemispheres, and (2) the earth is actually closest to the sun in early January.  The difference in energy received is simply overwhelmed by the difference in angle and daylength. 

It does make me wonder, though, whether southern hemisphere seasons are more extreme--with the effects added together--than those in similar latitudes and situations in the north.

Citizen Science Phenology

Poking around the Web as I investigated the idea of phenology*--a preoccupation of Thoreau's and many 19th century contemporaries--I discovered that there is still data to be gathered--it's not simply a 19th century hobby--and WE CAN HELP.  The National Phenology Network (whoda thunk?) has a citizen science project called Nature's Notebook that allows anyone who is interested to enter a location they want to observe over time, choose species of plants and/or animals they want to collect data on, and then upload all this on a regular basis to their database.  The nature of the observations needed differs depending on the species.  If you were watching a white oak, for example, you would record any buds opening, leaves expanding, flowers blooming, leaves turning, and so on.  For an animal like the wooly bear caterpillar (which metamorphoses into a tiger moth), it might be the presence of caterpillars, their feeding, the presence of adults, their mating, and so on. 

Of what use is this data?  One urgent need is to track the effects of global warming on ecosystems, and because phenology records have been kept for a long time, these are particularly valuable.  (Henry Thoreau's own century-and-a-half-old records have even been pressed into service to show that spring temperatures have been arriving earlier than ever before.)  The Nature's Notebook site lists several recent discoveries made with their data.

I was so pleased to find usefulness for my interest in nature, that I immediately signed up; yesterday I uploaded my first observations.

If you'd like to get involved, here are some tips.

· Think about where you can observe (your site) that is very accessible and not too close to a building: you choose when you want to observe, and how intensively, but in times of rapid change (spring, fall) frequent observations (every few days) will be more useful in pinpointing timing. (I chose my own yard to avoid the time needed to travel.)

· When you begin to choose species to observe, you will notice that data is only being collected on certain species. (I was disappointed to discover I would not be able to enter data on my beautiful scarlet oak.) Some, called calibration species, are especially valuable to observe because they are widely distributed, and so allow comparisons over much of the US. In the case of plants, it may be valuable to observe several individuals (though not near neighbors). Of course, make sure you correctly identify what you will observe!

· Be careful not to get in over your head; choose just one or a few species to start with. (I blithely signed up for three tree species and two grasses, and was surprised to find out how long it took to observe all the details and then upload them; I'm hoping I get faster with practice!) When you have become familiar with the time commitment, you can always add more species, or more individuals of the same (plant) species.

· Finally, I had trouble getting through the site set-up process, maybe because I was using Internet Explorer; the website is optimized (I was told later) for Firefox and Google Chrome.

· Other questions you might have will probably be answered in the FAQ

To see the big picture, maybe figure out what is most needed in your area, you can use the Phrenology Visualization Tool to see where in your state and nationwide data is being collected, and on what species. (I found some surprises here.) You can even get data to analyze yourself. These pages are back at the original USA-NPN site.

NOTE that there are other citizen science initiatives that might interest you. Internet-based citizen science started years ago with Seti@home, which put idle home computers to work analyzing radio telescope data from space in search of intelligent extraterrestrial signals. A modern one I've participated in is Zooniverse, which began by putting peoples' eyes and minds to work classifying objects from the zillions of space telescope images, and which has now branched out in interesting ways. These do not get you outdoors the way Nature's Notebook will, though!

*Phenology refers to key seasonal changes in plants and animals from year to year—such as flowering, emergence of insects and migration of birds—especially their timing and relationship with weather and climate. --Nature's Notebook

For Spacious Skies

Take some time each day to look at the sky.  I am trying to begin each day with a few minutes outside, coffee in hand, looking up.

Block Island Sound, RI, September 7, 2013, by the author.

 

Thanks to the efforts of the late Jack Gordon's For Spacious Skies, I find myself looking at clouds more and more.  But I make two mistakes: either (1) I enjoy their beauty without thinking about how they form and relate to weather, or (2) I think about how they form and relate to weather without enjoying their beauty.  I probably get nearest the happy medium when, rather than simply gazing, or fixating on whether they're stratocumulus or altostratus, I instead see a cloud as dynamic atmosphere made visible: air roiling, temperature changing, and water molecules ricocheting around before my very eyes.  To "see" clouds this way, you need to know a little physics and chemistry.  And after another post or two, you'll be able to see clouds this way, too.

 

To start with, clouds do NOT form because the air is like a sponge that can hold only so much water vapor, and cooling the air is like squeezing the sponge more and more, yada yada yada.  That was what I was taught, believed for many years, and taught many 7th graders (may they forgive me).  As an explanation, it works pretty well, but is simply wrong.  So what is the truth?

The first thing to understand is that water is evaporating and condensing all the time.  That means that a cloud is less a "thing" than it is a dynamic PROCESS.  To understand it, we will start with the fundamentals. 

1. All molecules and atoms move, and they move all the time.   Gas molecules bounce off each other, molecules packed together in a liquid jostle each other, and molecules locked into a solid simply vibrate--but all are in motion.  In a gas, molecules are separated, so they zing around and ricochet off each other like pool balls--with the difference that, unlike on a pool table, the collisions of gas molecules are perfectly elastic--so the balls never "run out of energy" the way pool balls eventually do.*

image from: http://saburchill.com/chemistry/chapters/chap033.html

2. Moving molecules have kinetic energy which is a consequence of their mass and speed.  (The equation for kinetic energy is E_K=mv², which means that heavier, faster-moving molecules have more energy than lighter, slower ones.  And the speed (v, for velocity) has a big impact on energy, because this number is squared.)  We experience this energy of movement as temperature, because temperature is proportional to the average kinetic energy of a sample of molecules.  In short, the warmer something is, the faster its molecules are moving.  Try to picture this when you hold a hot cup of coffee!

3. Every water molecule has a little positive charge at one end, and a little negative charge at the other.  Because of this, water molecules cling to anything with an electrical charge--including and especially each other.  (Remember learning in school that "opposites attract."

What does all this have to do with clouds?  Next time we'll look at evaporation and condensation.

Sunset over Block Island Sound, RI, September 7, 2013, by the author.

*By the way, those gas molecules are moving fast.  As a rule, the speed of gas molecules is about equal to the speed of sound in that same gas.  In air under normal conditions, that's rather more than seven hundred miles per hour.  But they don't usually get too far, since on average air molecules are only spaced 10^-5cm apart, so that a single molecule collides on average five times per nanosecond.  (1ns=one billionth of a second.)  That's fast-moving but mighty small game of pool!
Info from:
http://en.wikipedia.org/wiki/Speed_of_sound
http://www.ems.psu.edu/~bannon/moledyn.html