Saturday, January 28, 2012

Why Does Lightning Appear Blue and Cause a Rumble?

Fans of the film Rocky are very familiar with the character played by Burgess Meredith.  While Mickey, Rocky's lovable, old, grumbling boxing trainer has a lot of memorable lines, I particularly enjoy the one he uses to motivate Rocky during his training: "Kid...You're gonna eat lightning and you're gonna crap thunder!"  This hilarious line, delivered ferociously by Meredith, is not without educational merit: the sound of thunder always follows a lightning event.    

While everyone has observed the awesome phenomenon known as lightning, most do not know what they are seeing, nor the cause for what they hear afterwards.  Still, most are aware that one precedes the other (Rocky would never, for example, eat thunder and then crap lighting).

The reason for the order is simple: a lightning bolt causes a flash of light, which travels at 300,000 km/s (the speed of light), and the sound it produces, thunder, travels through air at about 0.34 km/s (the speed of sound in air).  So, the light from a flash of lightning that strikes one kilometer from you reaches your eyes almost instantly (1/300,000 of one second), while the sound it produces reaches your ears three seconds later.  We cannot easily fathom a ratio of one million, but in our atmosphere, that is just how many times faster light travels than sound.

Thursday, January 19, 2012

Earthquakes and Emotions

While watching a Nova documentary about earthquakes, I could not help but notice the many parallels between the huge releases of energy by the Earth's crust and the huge releases of rage that people experience when they suppress their negative emotions for too long.  We have all witnessed somebody having a personal meltdown, and most of us have snapped to some degree at some point in our lives.  The results are not pretty, and can leave those around us distraught.  While keeping one's feelings withheld for extended periods of time is a tendency that should be avoided, it serves as a fitting backdrop for a discussion on seismic activity.

As you compress a spring from its equilibrium position, its coils store what is known as potential energy.  If the spring is released, this stored energy will be converted into kinetic energy and a vibration will ensue.

Imagine now that instead of a spring or elastic band, it is a less malleable substance that is being compressed, like a steel rod.  Although a steel rod is much sturdier than a typical spring, it can actually be deformed ever so slightly by a large compressive force.  In this compressed state, the steel rod stores potential energy also known as strain energy (energy due to deformation), and would snap back if released, just like the spring.  While the rod deforms less than the spring, it actually stores more potential energy since more work was required to compress it.  What this means is that a compressed rod will rebound more violently once released.

Earthquakes occur when the strain energy stored in the Earth's crust is released over a very short duration of time.  The period of time over which this crust deformation accumulates is usually a number of years.  Inch by inch, adjacent sections of crust move with respect to one another.  The boundaries in the Earth where such tectonic plates meet are known as fault lines.  Unlike the steel rod, whose cross-section is measured in square inches, these tectonic plates are measured in square miles.  A bigger cross-section is linearly related to the amount of strain energy stored for a given displacement.  So, whereas a rod may store many kilojoules of energy, the amount of energy stored in a section of displaced rock may be measured in how many Hiroshima atomic bombs it is equivalent to (note that a 9.0 on the Richter scale is roughly equivalent to one thousand of them).

This massive amount of energy is only dangerous if it is released over a short period of time, as this constitutes a powerful energy release (P = E/t).  All quakes are powerful, as the time of release, t, is always small.  This massive power is spread over a reasonably large surface area, and this ratio describes the intensity of the seismic activity (I = P/A).  Finally, the Richter scale is a logarithmic (base ten) scale that measures the intensity of the tremor.  As such, an R = 7.0 is ten times greater than a 6.0, and one hundred times greater than a 5.0.

Still, it all comes back to the amount of energy that is stored, and this is directly related to the amount of relative slip across fault lines.  The vast majority of earthquakes are so minor that we do not notice them (R < 3.0).  They are the result of a small amount of deformation that builds up over a relatively short length of time.  The mechanism for release is the same for both small and large earthquakes; the difference is that small earthquakes release their stored energy before too much accumulates.

These small earthquakes are an illustration for how we should all manage our emotions.  It is healthy to vent our negative feelings every so often.  When you have a bad day, it may suffice to play some sports and let off some steam.  This is like a harmless 3.0 earthquake.  When several bad experiences pile up over the course of a week, and you haven't had a chance to discuss it with someone close to you, it can all come out in a minor fit on Friday night.  Your spouse may not appreciate being subjected to a 5.0 on the Richter scale, but the dust will settle, and the extent of the damage will be minimal.

Tuesday, January 10, 2012

Hollywood Films Get Space Travel Wrong

As the space ship in the 1986 film Aliens moves towards a mysterious planet, the cosmonauts aboard gaze suspiciously at the foreign body with their feet firmly pressed against the ship’s floor.  The sci-fi adventure has barely begun, and already, the laws of physics have been ignored due to a common imbalance in Hollywood: too much fi, too little sci.

I want to be clear about something: I am an avid fan of science fiction movies, whether or not they are set in space.  In fact, I was thoroughly entertained by Aliens, the sequel to Alien - so much so that I watched it recently for the second time. 

As the film is set in the distant future, it is sensible that several technological leaps have been made by mankind.  I am comfortable with the intelligent robot that is a part of the crew.  I am intrigued by the sensitive motion detection equipment that they use.  What makes me queasy is when the most basic law of motion is inexplicably defied.

When advances in technology occur, they lead to more robust tools.  However, these tools, no matter how fantastic they are, must operate within the constraints of the universe.  Otherwise put, technology is dynamic, but exists within an operational framework that is static.

When a space travelling Sigourney Weaver stands up on the surface of a ship, this implies that there is a set of contact forces between her feet and the surface.  A force, commonly referred to as the normal force, is pushing up onto her feet.  Unless you are currently undergoing a vertical loop on a jet airplane, or happen to be reading this article while in a space orbit, the normal force is currently acting on you.

Friday, January 6, 2012

No, the World Will Not End on December 21, 2012

Let's begin this year by, as the oracle put it to Neo, getting the obvious stuff out of the way.  The widely held prediction that the world will end on this year's winter solstice holds about as much water as a shot glass.

The claim, which stems from the Mayan calender reaching its end, is like many other pseudo-scientific ones that float around the virtual ether: it lingers because it cannot be proven false.  Well, not until the end of 2012, that is.

The end-of-the-world claim can, however, be deemed baseless with relative ease.  I  think that any reasonable person realizes this.  If today's best meteorologists equipped with modern technological tools cannot accurately predict the weather some weeks into the future, how could the Maya accurately predict the "End of Days" moment thousands of years prior?  The obvious answer is that the Maya could not and did not.  But then, I suppose that any devout believer of the silly prophesy would not be swayed by a scientific argument.

Truthfully, I would rather not pay any attention to a debate that cannot be won.  Unfalsifiable statements like, "A flying saucer passed over my house last night," amount to nothing more than noise.  It is a waste of my time and yours to worry about bogus prophesies (is there another kind?) when there is so much richness to be found in real science.  Yes, interpreting actual science requires some logic and a certain degree of effort, but unlike mysticism, it is rewarding.

You know, some "End-of-the-worlders" have modified the terms of their prophesy recently.  They now claim that the world as we know it will end on December 21, 2012.  Well, this is the same sort of cop-out as we are accustomed to seeing in horoscopes, which provide loose predictions that are open to various interpretations.

Every now and then, when horoscopes try to get too precise, they risk exposing how fraudulent they truly are.  For example, my horoscope has alerted me that I will meet the love of my life countless times in recent years.  If the stars really knew me, they would know that I met the love of my life thirteen years ago.

So, I am happy to get this little bit of Hocus Pocus out of the way now.  I will not bring up the implications of the Mayan calender again before the fateful day.  And then, on December 22, I will post the following tweet: "I told you so."