Airplanes That Seem to Hover

Last year I posted an article about the fundamental principles behind how a subsonic aircraft works.  In summary, an airplane takes off once a critical speed is reached: the greater the speed of the wings relative to the air being cut by them, the greater the pressure difference between the air on the top and bottom of the wings, and the greater the lift force.

Now, I would like to address a particular concern about airplanes that some of my students have had.  Have you ever looked up at an airplane, and had the impression that it was barely moving?

Helicopters, hot air balloons, and some supersonic aircrafts possess the ability to hover, but subsonic aircrafts do not.  As already mentioned, the only reason that a commercial plane can maintain a given altitude is because it is moving horizontally with respect to the air around it.

So, what is going on here?  I too have looked up at aircrafts as they descend and have remarked, on occasion, that the plane seems to be moving at a snail's pace.  Sometimes an airplane flies above me as I cruise along the highway, and my impression is that I am in fact moving faster than it relative to the ground.  Is it an optical illusion?  Let us investigate.

The Wondrous Night Sky

When my daughter recites twinkle, twinkle, little star, I am tempted to answer her question regarding what they are: "Giant collections of particles moving in all directions colliding into one another at high speeds forming larger particles in fusion reactions that give off heat and light..."  And then I remember that she turns three this summer.

I got to thinking about stars when a couple of callers rang me up the other day on my call-in show.  OK, I don't have a call-in show.  It was just a couple of friends calling me at home with questions about stars.  They were either genuinely curious about these glowing masses or were poking fun at my passion for all things science.  I am going to assume it was genuine curiosity, and answer their questions below.

Pushing the Boundaries of Science Like Pushing a Vacuum

As far as division of labour around the house goes, my wife and I each have our own respective duties, and one of mine is vacuuming the house.  I kind of enjoy mindless activities like this one, because it allows me to shut off my brain for the better part of thirty minutes.  But with the mind unfocused, it is at once free to wander; I find that I do some of my deepest thinking while under the hypnotic trance of the vacuum's purr.

Once, while seeking out lose dirt and dust-bunnies with my trusty dust-sucker, my mind began to wander even further than normal.  I began to see clear parallels between my search for dust around the house and humanity's pursuit of science in general.  Before I go any further, let me assure you that I realize that only one of these two endeavours is of great importance, and it is not the one that involves me pulling out the couch, cleaning behind it, and pushing it back.

Dust around the house tends to accumulate in the places we encounter the least.  Sections of the home in plain sight are relatively free of such particles, as these areas are well-travelled.  The dust gets displaced to a new spot due to the relative motion of air around it.  If this new spot also sees regular activity, the dust will inevitably move yet again.  It will only settle permanently in a quiet, unused spot within the room (usually behind something heavy, to the vacuumer's chagrin).  The phenomenon is much like snow on a high-traffic ski slope, which tends to build up on the two outer edges.

How then is vacuuming like scientific advancement?  Imagine that each piece of dust to be collected is like a scientific mystery to be solved.  Much like the loose dirt that we wish to suck up, the vast majority of the mysteries associated with the physical world are well-hidden - that is, unless we search for them explicitly, we will not even know that they exist.

Each room within the house may be thought of as a scientific pillar, each with its own particular sort of unsolved mysteries waiting to be uncovered.  We could have physics in the family room, chemistry in the kitchen, biology in the bathroom, and so on.

In the early going of modern science, the house was a complete mess throughout.  As almost no one was taking part in scientific research, dirt was evenly distributed.  When Isaac Newton decided to begin to clean the house, he began with what he interacted with most on a daily basis - that which was the most visible.  In the late seventeenth century, he uncovered the basic principles of mechanics (the motion of bodies) and geometric optics (the behaviour of visible light).

As the study of physics moved along, research in other fields of science began.  Before long, each room in the house was being cleaned in parallel.  The science research landscape was a busy one indeed during the twentieth century. 

As the dust settles, and the twenty-first century soldiers on, we may look at the house and conclude that it is clean.  Scientific principles may be invoked to explain just about everything we typically interact with.  That which was most obvious, that which presented itself, has been sucked up by the scientific research community.  All that remains to be discovered in the present science landscape is that which is not in plain sight.