Ah, inertia. We all have it, especially at night sitting on the couch reading a book or watching a show and not wanting to move for anything. But maybe that is sloth, not inertia. So what is inertia then? Well inertia is defined as the tendency of an object to resist changes in its state of motion. Still sounds like sloth, doesn’t it?. But lets clarify a bit. What is meant by "state of motion?" Well, the state of motion of an object is defined by its velocity, so we could reword inertia like so - the tendency of an object to resist changes to its velocity. All matter has velocity. If something is not moving, it is still considered to have velocity - a velocity of zero.
So who was the nutcase that started thinking about inertia and defining (through words and mathematics) what it actually means? Well, the nutcase was Isaac Newton (1642 - 1727). And let’s just say Isaac was not a couch potato. This abnormally intelligent and motivated individual was the antithesis of inertia in every form. If you ever (I hang my head in shame because I haven’t - yet) read his "Philosophae Naturalis Principia Mathematica" (published in 1687), you will find inside his three laws of motion. What is it with individuals named Isaac setting down three laws anyway? . . .
Newton’s (I’ll use Newton not Isaac from now on so as not too confuse) first law was defined by him as "every body persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it." These bodies are said to be in equilibrium with a constant velocity until they are subjected to unbalanced forces. Now it could be argued that I am unbalanced, but while I am on the couch reading my book at night, I can be considered to be in equilibrium because thoughts are not considered matter, so that kind of unbalance is not dealt with in Newton’s first law. Freud, however, may have so notes on this matter. . . . But I digress.
So now that we know my body is in equilibrium on the couch, we may want to know why that is so. Well, my body is being subjected to balanced forces and therefore my velocity is unchanged. Gravity is pulling me into the couch cushions and the couch is pushing me back up. Equal and opposite forces keep my body in a constant state of velocity. Now for me to actually move, some unbalanced force must give me a shove and overcome my inertia, or I must use my muscles to do the work. And my wife, at times, knows how hard that can be. And the larger the mass of the object, the harder it is to overcome its inertia as well. And no, I will not step on the scales.
Without getting into diagrams and mathematics, I think inertia is pretty well defined here. I’ll just settle back on the couch now, grab up a novel, and use my inertia to resist any unbalanced forces coming my way.
Tune in next Sunday for another exciting, exhilarating, fun and educational Weird Science article. . . .
Well - educational anyway.