In my physics book, it explains how Newton formed his theories, through his deduction and experimentation. As I was reading it, it made me laugh when I realized that if his theories weren't established as scientific fact, and we're just being introduced now, I would've though it mystical and contrived. I would've thought he was a crackpot. Let me demonstrate this with this bit of dialogue which involves Sir Isaac Newton relating over his discoveries to a 'scientist' named Zebulon. Admittedly, many, if not most of Zebulon's arguments are tenuous at best, but Newton appears equally guilty of departing from the land of reality.

Newton: ... so you see, an object at rest remains at rest, and an object in motion continues in motion with constant velocity, unless it experiences a net external force.

Zebulon: But that is absurd, and I can easily show you why. Observe this small ball, a child's toy. I'll place it on the ground and set it in motion by kicking it. (Zebulon kicks the ball, watches it tumble about five meters or so, until it finally reaches a stop. Zebulon then turns to Newton, with a smug look on his face, which dares him to "explain that!"). So it is settled then. The orb was placed in motion yet it came to a stop without any forces being exerted on it.

Newton: I see why that might trouble you, so let me explain. The ground, upon which your orb was tumbling, exerted a force onto the ball, which slowed it down, eventually causing it to stop.

Zebulon: Are you claiming that a flat piece of land can exert a force on an object which is upon it?? Did you see the ground quake and strike the ball? How could the ground have applied a force onto the ball? Isaac, you're positively mad!

Newton: hmm, again, I see why that would trouble you, but it can be easily understood if you listen carefully. When an object comes in contact with another object it exerts a force called friction. The friction created from the orb's contact with the ground is the force which stopped the motion of the orb.

Zebulon: So you will insist that an object in motion stays in motion, despite glaring examples showing otherwise, and then, you will create an invisible and imaginary force, which has no basis in logic or reason, in order to clear up the discrepancies between your theory and reality? Are you going to insist, with a straight face, that the floor exerted a force onto the orb which was undetectable by the eye?

Newton: Might I suggest you think about it over night, so we can discuss it further tomorrow. Maybe after pondering it a bit you might reach different conclusions.

Zebulon: "Ok, Ok, let me give you the benefit of the doubt. Let us assume for argument's sake, that this invisible force called friction exists. I suppose what you're saying is in the realm of possibility, after all, the two objects are in contact with each other, and maybe forces undetectable to the eye are transmitted through this contact.. But if an object in motion is to continue in a straight line motion, like your theory states, then what keeps the planets and the Earth from straying from their orbits? Why do they go around in circles instead of the straight line which you claimed all objects would travel on."

Newton: "Well, there is another force which I call gravity. Objects of mass exert a force of gravity onto other objects. The force exerted is proportional to its mass, and inversely proportional to the square of the distance separating the two. So a planet of tremendous mass will exert a considerable force on its moon, while the moon also exerts an equal but opposite force onto the Earth. Gravity, this is the force that keeps us tethered to the ground, keeps us in orbit around or sun, and pulls everything, regardless of weight or composition, falling to the ground."

Zebulon: "You're mad, Sir Newton, I swear by God, you're positively mad! You suggest a theory which contradicts all observations, and then you attempt to resolve these discrepancies by conjuring fanciful forces. A force which can act upon an object without any movement? Or ghostly forces which can act at a distance? I firmly hold that anyone or anything which can control an object without being in contact with it, must be in league with the devil. Even when adhering to your fictional forces, there are significant contradictory and irresolvable problems. If an object at rest has a net external force of zero, then how can that watch sitting upon the table be at rest. After all, isn't gravity working upon it? Oh, I suppose you'll just create another force which will help you shoehorn your square peg down my throat. Ah, and if gravity were to exist then what prevents the moon from crashing down at our feet? Gravity is the force which keeps us tethered to the ground you say? Where else would objects go but down. You don't need a force to know that objects naturally travel downward.

"An object in motion stays in motion. Yet nowhere in the known world is that observed. How curious."

This was exactly the opposition Newton faced when introducing his theories, especially that of gravitation. In mediaeval philosophy, the idea of action at a distance was discredited through its association with ``magic'' and the supernatural. So here comes Newton, saying ``Hey, guess what? The planets go round the sun because of an invisible force that acts at a distance through no known medium!''. Of course he is ridiculed---the idea of action at a distance is even more ridiculous than the idea, proposed by some, that each planet has an angel that guides it around.

(This is really more Galileo than it is Newton, but that changes little.)

Lith demonstrates how Newton too requires us to believe in certain concepts (like inertia) which are unachievable in the Universe. This is taken as a measure of crackpottedness (cracked potty -hood?). In particular, it is argued that telekinesis is in a similar state: believing in it means believing in concepts unachievable in the Universe.. I would counter that Lith is of course correct regarding unachievability of zero force exerted, but is drawing the wrong conclusions.

Newton's laws are an axiomatic definition of force. Force is a somewhat imaginary construct: for instance, it is invisible. But so is length. Instead, Physics (being, after all, the science of measurement) makes do with telling us how to measure it. You measure length by using a piece of string; you measure force by using a spring (better methods exist for measuring both, of course; switching to a better method just requires callibration against the old method, and a demonstration that the new method is indeed better). In particular, to measure friction, you just attach a spring to an object, tug at the spring, and note that the spring extends. Newton's laws give a framework for understanding why a spring would indeed measure force. But you may think of it backwards: giving a mathematical theory of how springs behave, it is easy to reformulate it around a new concept of "force". This is essentially what Newton did.

So what's with inertia? Why do physicists insist on the "fact" that "objects continue at a constant velocity if no net force is applied", when we all know that force is always applied?

It's just Newton's first law. Newton claims that there is this measurable thingy called "force". Zebulun wants to know how he might see it in action. Newton claims that force is what changes velocity; force is the only thing that can change velocity! Zebulun keeps seeing velocity changes, so that settles the question of seeing force in the world. But it raises a host of new questions: for every velocity change that Zebulun sees, Newton (or some other physicist) has to find a force! And these forces must "explain away" the velocity change using Newton's laws; no new laws are permitted (even Relativity keeps Newton's laws intact, but changes the interpretation of some of the quanitities appearing in them).

Besides, you can see an empirical demonstration of the first law. You can't have zero net force acting on an object, but you can reduce the net force arbitrarily low. It's called measurement. It's not accurate, but that's life. And indeed Newton's laws explain everything they claim to (or at least, they did, if you apply minor corrections for Relativity and don't work on the very small scale, where measurement artefacts (aka Quantum theory) show up).

Contrast this with telekinesis. Whereas changes in velocity are everywhere to be seen, telekinesis is nowhere to be seen. Occasionally one is told that TK may be observed at some lab. Invariably, it turns out that TK will only be seen under extremely restricted circumstances (the right person has to operate the measuring apparatus, the right person has to be tested for TK, it has to be done at the right lab, and the right audience must be present, or they will broadcast negative mind energy and negate the TK effect). The Newton vs. Zebulun Metaphysical Catfight takes place in the lab: all effects are real and easily observed; the question is if a single mathematical theory can explain them all. The TK vs. Science Metaphysical Catfight takes place in our imaginations: the existence of none of the effects has even been demonstrated, and yet TKers want to talk about their theories of how it all occurs.

No contest.