Motion
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From: Randy Poe on 20 Sep 2005 12:39 TomGee wrote: > Randy Poe wrote: > > TomGee wrote: > > > Sam Wormley wrote: > > > > Newton is much more precise > > > > http://scienceworld.wolfram.com/physics/NewtonsLaws.html > > > > > > > > 1. (Law of inertia): A body at rest remains at rest and a > > > > body in motion continues to move at a constant velocity > > > > unless acted upon by an external force. > > > > > > > > > > > Well, well, Worms, you're starting to support your beliefs with actual > > > excerpts from your websites! Very good, keep it up. > > > > No matter what well-known fact you choose, somewhere on the > > internet is somebody who disbelieves in it and writes volumes > > on his (occasionally her) disbelief. > > > > > According to your buddy PD, though, the 1st law includes a claim that > > > the body has no internal force to keep it in motion. Did you leave > > > that out, or don'tcha agree with PD? > > > > That's correct. There is no force that keeps bodies in motion. > > Forces only act to change motion. > > > > > So you agree with PD and Worms. And Newton, yes. > What else is new? Certainly not that. It's centuries old. > They only believe > that because they were taught to believe that. Well, also because it works as a valid model of reality. > Anyone with a real > brain would be able to support such a wild statement, but I see you > offered none, so that's just your opinion. OK, fair enough: what keeps the planets going, along with every satellite and chunk of space junk, if they need propulsion in order to keep going? > > > PD claims such accelerations do not amount to a change in kinetic > > > energy. Do you agree or disagree? > > > > You are misreading something. A change in speed constitutes > > a change in kinetic energy. > > > > > No, no misreading. Read it for yourself word for word in this same > thread. Can you quote the relevant passage? > > Perhaps you garbled a description of circular motion, in > > which the force acts perpendicular to the velocity. In that > > case, the acceleration results in a change of direction, > > but not of speed, and the kinetic energy is constant. > > > > > No, no garbling by me. If you garbled the meaning, you would hardly be the one to know, would you? You'd only have your garble as reference. > > > So the force in 2. above is different from the force of bodies striking > > > each other? > > > > When bodies strike each other, the forces obey Newton's laws, > > including the third law. > > > Then PD must think those laws apply only to bodies in classical physics > and not to quantum particles. I've seen nothing in PD's writing to indicate such a view. > > > In 2., the force makes a body move in the same direction > > > of the force, > > > > The acceleration is in the direction of the force. That may or > > may not cause motion toward the force. Generally not. If > > something is moving past you and you give it a kick as it > > goes by, it won't change direction and start going straight > > out from the direction of your kick. It will still have a > > component due to the original motion. > > > > > Yes, I know, but PD does not know that. I've seen nothing in PD's writing to indicate such a view. In fact, you were putting your garbled interpretation on something PD just wrote, which did not resemble in any way what you are saying. > > > but in 3., the force of one body makes the other move > > > away from it. > > > > No. That is really garbled. > > > > > No, it's not, read it up above, it's exactly what PD said. I read it. > If it > proves anything it's that his brain is garbled. Words are written. They are then paraphrased by you. I agree with the original words. I find yours seriously garbled. Hmmm... where did the communication error occur? > > If A pulls on B, then A gives an > > acceleration of B toward A. > > > Yes, but PD did not say, "IF A _pulls_ on B,...." He makes no > distinction of pulling or pushing. The principle applies in either case. If A pushes on B, then B pushes back. If you sit on the floor, the floor pushes back with enough force to support you. If it did not, as happens if you are sitting on a weak tree limb, or in midair, you fall. > > That's law number 2. At the same > > time, A is pulled toward B. That's law number 3. The fact that > > A is pulled toward B does not contradict the fact that B is > > pulled toward A. > > > No, that's not law number 3. Yes it is. > Now you're getting confused just like PD. Words are written, then paraphrased by you. I agree with the original words, I disagree with the paraphrase. Where did the communication break down? Hmmm.... > > If you hit a piece of wood with your fist, you might dent > > the wood (law #2). That does not prevent the wood from denting your > > hand at the same time (law #3). > > > No, not so. Both relate to the 3rd law of action/reaction., The denting of the wood happens because the forward force you impart to the surface gives forward motion to the surface. The relation between force and acceleration is certainly NOT law number 3. - Randy
From: Don1 on 20 Sep 2005 13:25 Randy Poe wrote: > Don1 wrote: > > This is what happens with any > > vehicle and propellent - why a rocket can't go faster than the > > propellent is expelled. > > Incorrect. A rocket is not limited to its propellant speed. > > - Randy Well I dont know Randy, is that according to the law of action equals reaction? After all of the propellant has been exhausted isn't it all going backward at the same speed as the rocket is going forward? Isn't that what equilibrium is all about? Don
From: odin on 20 Sep 2005 13:31 >> Incorrect. A rocket is not limited to its propellant speed. > > Well I dont know Randy, is that according to the law of action equals > reaction? After all of the propellant has been exhausted isn't it all > going backward at the same speed as the rocket is going forward? Nope. The propellant being exhausted does not have to be going backward at the same speed as the rocket is going forward. Where did you get that idea? Isn't that what equilibrium is all about? Nope. Keep trying.
From: Randy Poe on 20 Sep 2005 14:11 Don1 wrote: > Randy Poe wrote: > > Don1 wrote: > > > This is what happens with any > > > vehicle and propellent - why a rocket can't go faster than the > > > propellent is expelled. > > > > Incorrect. A rocket is not limited to its propellant speed. > > > Well I dont know Randy, is that according to the law of action equals > reaction? Yes. If a rocket of mass 100 kg is moving past me in space at 100 m/sec, and it ejects ping pong ball backward with mass 0.001 kg and relative velocity 1 m/sec, the ping pong ball has (from the rockets frame of reference) a momentum of 0.001*1 kg-m/sec. The rocket will get a recoil from the ping-pong ball, and end up moving at 100.00001 m/sec. Even though the muzzle velocity is 1 m/sec, the velocity of the rocket is not limited to 1 m/sec. If it throws mass backward, no matter how tiny, it gets a boost forward. That is indeed the law of action and reaction. > After all of the propellant has been exhausted isn't it all > going backward at the same speed as the rocket is going forward? No. Momentum is the conserved quantity. When the rocket first starts, the small mass of the exhaust moving very fast, causes the large mass of the rocket to move forward only slowly. Eventually, if the rocket is faster than the exhaust velocity, then from our point of view the exhaust will be trailing the rocket, moving forward but not as fast as the rocket. > Isn't that what equilibrium is all about? No. Think about the recoil from a gun. If a bullet leaves the gun at the speed of sound, do you think the gun kicks back at the speed of sound? If the gun outweighs the bullet by 100:1, then the speed of the gun will be about 100 times less than the bullet. (This is complicated by the fact that there are hot gases which also get some of that momentum). - Randy
From: Sam Wormley on 20 Sep 2005 14:23
Don1 wrote: > Well I dont know Randy, is that according to the law of action equals > reaction? After all of the propellant has been exhausted isn't it all > going backward at the same speed as the rocket is going forward? Isn't > that what equilibrium is all about? > Conservation of Momentum (is what Shead needs to learn). http://scienceworld.wolfram.com/physics/ConservationofMomentum.html http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html |