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First my apologies for the delay, I have been working 10 hour shifts and then pretty much been going straight to bed.

The math version is also coming it's just been a lot of work (especially as the census was that people wanted to the equations displayed right).

The math diary will be out Friday or sooner.

Now then let us jump into the world of Newtonian Physics, also known as Classical Physics.

First a confession of sorts, the past diaries have all been about Newtonian Physics and yet I never introduce Newton's Laws (which are the foundation of this branch of physics).

I did this intentionally because first it was how I was introduced to physics. Also because I wanted people to see that a limited and yet useful understanding of physics can be achieved with absolutely no understanding of Newton's Laws.

Now then, I introduce to everyone the basis for Newtonian Physics and frankly the genesis of physics itself (and no that is not hyperbole).

  1. A body at rest stays at rest and a body in motion stays in motion; unless acted upon by an external force
  1. Observed from an inertial reference frame, the net force on a particle is equal to the time rate of change of its linear momentum: F = d(mv)/dt

3)Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction.

Now I have tried to somewhat simplify the laws but no worries I am going to devout time to explain and talk about each.

1) A body at rest stays at rest and a body in motion stays in motion; unless acted on by an external force.

The first law of Newtonian Physics is often simply referred to as the law of inertia. Inertia though is also a property of matter and can be observed in 2 distinct ways as noted above.

The first display of inertia is that an object that is not moving stays that way unless it is acted upon by an external force.

This should be intuitive, we see it all the time and yet it is profound. If this was not the case then the world as we understand it would just not be possible.

The second display of inertia is that an object in motion stays in motion.

This probably is not as intuitive as for example a hockey puck struck by a hockey stick does not carry on forever. Nor does a car coast indefinitely. And yet such examples are deceptively complex. See you have to account for the sum total of the forces and there is more then just one force to account for. In fact what is missing is friction which simply stated (for now, I'll devout an entire future diary to friction) is resistance to motion.

Thus your car encounters friction (caused by the wheels among other things) and slows down.

I want to briefly talk about the power of inertia and to do so I want to draw upon  Star Trek. In Star Trek the heroes (and villains) travel around at faster then light speed. Now I do not want to get into the physics of that, instead I want to talk about what is known in that universe as 'inertial dampeners'. The physics of which (to date) do not exist, but what would happen if such technology did not exist?

Quite simply when the ship accelerated past the speed of light it would crush every bone in the body of any aboard the ship. And that's just the obvious effect. It would also cause anything not bolted down to rip though the ship.

Inertia is one of the most important concepts in physics. While it is not the only important thing in Newtonian Physics it's effects are felt profoundly (and in actuality much of the complications to Newtonian Physics are in fact trying to account for inertia).

2) Observed from an inertial reference frame, the net force on a particle is equal to the time rate of change of its linear momentum: F = d(mv)/dt

This is often simplified to force is equal to mass times acceleration (F = m * a).

Those familiar with derivatives should almost immediately see where that equation comes from. To those that do not, I will simply assert that the derivative of velocity with respect to time (dv / dt) is acceleration. And that as mass is a constant one can not take the derivative with respect to time of it.

Unlike the first law there is little to explain as this is effectively just an equation. And there is little verbal description I can give about this law. Rather I think it more effective to see it used in practice. As such I want to devout at least the next diary to exploring the implications of the 2nd law and how it is used to solve Classical Mechanics.

3)Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction.

This is perhaps my favorite of the 3 laws (I will confess that some of that is because unlike the 1st law there is no complication due to full consideration of the law. Or because unlike the 2nd it is not a mathematical construct but rather a concept.)

This also might be the most well known aspect of Newtonian Physics.

Basically when a force is exerted upon an object that object also exerts an equal and opposite force.

For example you know why a punch hurts a person's hand? Because the force of that punch is directed back at the hand and the puncher.

Or for example if you were to take a rubber disk, place it on a frictionless surface and then slide a second rubber disk straight the first disk. There would be a collision and the first rubber disk would move forward at a set speed and the second rubber disk would be moving backwards at the same speed.

For those reading this that use guns, the 3rd law is why you feel recoil.

Well that's all I have for now, I will remain around to answer questions. I hoped people enjoyed this and that it made sense. On Friday as I said I will publish  the math aspect of ballistic motion. After that on Saturday I will move back to the math light aspect and explore some examples of using the 2nd law to solve mechanics as well as highlight how using the concepts presented in the 1st and 3rd laws are useful for solving mechanics. Then on Tuesday I will move back to math oriented approach and mathematically prove the 2nd law.

Originally posted to drache on Wed Jul 01, 2009 at 06:32 PM PDT.

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