Kevin Gowen wrote:

<TRIM>

>>>> Mr Newton, I would like to introduce you to Mr Einstein.
>>> 
>>> 
>>> 
>>> Er, ok. You're not one of those types that think Newtonian mechanics
>>> is "old-fashioned" and out-of-date, are you?
>> 
>> 
>> Yes and no. I do know how to correctly identify a mechanical physics
>> problem.
> 
> You've done a very good job of keeping that secret.
> 
>>  > It's a common affliction of Star Trek fans.
>> 
>> Whereas Star Wars fans have it all sorted? Fine, I am neither a Star
>> Trek fan nor a Star Wars fan. I did see one Star Trek movie in a
>> cinema but I laughed at the wrong times, much like my reaction to
>> Star Wars. 
> 
> No, it's just that Star Trek tries to explain how its tech works, and
> throws about "quantum" every other sentence.
> 
>>>> Let's do an experiment. You are sitting on your chair. It's a 5
>>>> legged rotating one, no arms and no fancy gas cushioning. You are
>>>> pressing down with 100kg. You see your "sports" bag (weighing
>>>> 100kg) on the ground and remember there is a Hershey bar in it.
>>>> You pick it up and momentarily there is 400kg pushing downo on the
>>>> chair (you + the bag + the acceleration of lifting the bag)
>>>> [ignore the massive fart you let rip - too hard to measure].
>>> 
>>> 
>>> 
>>> I don't know where 200 kg of mass magically appeared from. Your
>>> experiment has violated the First Law of Thermodynamics, thereby
>>> shaking the very foundation of physics.
>> 
>> 
>> Nice try but I didn't say "200kg of mass".
> 
> Yes, but it would have been better if you did.
> 
>> In fact I clearly refered to
>> "the acceleration of lifting the bag". The bathroom scales you
>> suggested to use would measure this.
> 
> Unfortunately, acceleration is not measured in kilograms. The scale
> displays kilgrams because it divides the force measured by the
> acceleration of gravity. This is done through Newton's Second Law.
> 
>>>> You put the bag on your lap. There is now 200kg pushing down. The
>>>> phone rings and you rotate in your chair and the bag falls off.
>>>> There is now 100kg pushing down on the chair. Why aren't you
>>>> ejected into space when you drop the bag? Surely the chair was
>>>> pushing up with 200kg.So this magic chair has pushed up with
>>>> 100kg, rising to 400kg then 200kg, then suddenly back down to
>>>> 100kg. Suddenly the chair gives way and collapses. You are now
>>>> sitting on a pile of cloth,plastic and metal - but this magic
>>>> chair is still pushing up with 100kg of force.
>>> 
>>> 
>>> 
>>> A kilogram is not a unit of force; it is a unit of mass. I believe
>>> the term you want is "newton". I could understand your hypothetical
>>> better if you did not insist on using units of mass as if they were
>>> units of force.
>> 
>> 
>> If that is the case, why did you suggest using a spring based device
>> to measure the downward force
> 
> Because I have heard of Hooke's Law.
> 
>> when the correct way to measure force is it's
>> effect on moving a body of mass?
> 
> It's "effect"? I don't even know what that is supposed to mean. Who
> says that a mass acted upon by a force must be in motion? Push
> against a building as hard as you can. The building does not move,
> but you are still exerting a force upon it.
> 
> A similar example is one that might finally educate you. Two men of
> equal strength play a match of tug-of-war. The rope's midpoint doesn't
> move, but the two men are exerting forces. Equal and opposite forces.
> 
>> Regardless, kilograms and pounds are used to measure force (eg the
>> Pratt and Whitney F100s produce 25,000 pounds of thrust).
> 
> Gee, how many kilograms of thrust would that be? But, here's a good
> question for you (with round numbers for simplicity): A Pratt F100 is
> traveling at a constant velocity of 200 m/s as its engines produce
> 25,000 pounds of thrust. What is the force of aerodynamic drag on the
> jet? 
> 
> If a kilogram is used as a unit of force, that is nonsensical, and
> would render Newton's Second Law useless. The folks at BIMP seem to
> agree: http://www1.bipm.org/fr/si/base_units/
> http://www1.bipm.org/fr/si/derived_units/2-2-2.html
> 
>> Or  are you planning
>> on leaving the surface of the earth to perform your experiments
>> elsewhere? That would be interesting because then we would have to
>> simulate gravity using a large rubber band wrapped around you and the
>> chair. Is the chair now pushing up (towards you)?
> 
> With the same force I am pushing "down" on it (although "up" and
> "down" are meaningless in free fall).
> 
>>>> How does this magic chair keep pushing up with the exact amount of
>>>> force required?
>>> 
>>> 
>>> 
>>> Newton's Third Law. It's the same thing that makes rockets work.
>> 
>> 
>> So why didn't you blast off when the extra weight was removed from
>> the chair?
> 
> Newton's Third Law.
> 
>> Where did all that extra *force* from the chair go?
> 
> I knew that Newton's Third Law was poorly understood, but this is
> ridiculous. There was no "extra" force.
> 
>> Now let's use the bathroom scales again as they are a useful tool for
>> measuring force on earth.  We can calculate your mass using other
>> techniques so we can accept (for this hypothetical) that you weigh
>> 100kg. We place the scales under you to measure the force of your
>> mass pushing down and we know it is 100kg. But if the chair was
>> pushing up with 100kg then it should measure 200kg?
> 
> You ask a question like that, and you broadcast that you don't know
> what a vector is.
> 
> Why do you insist on using a kilogram as unit of force? But that is
> besides the point.
> 
> If my mass is 100kg, then I am pushing down on the scale with 980
> newtons. At the same time, the scale is pushing up on me with -980
> newtons. Thus, the net force acting upon me is zero. That is why I am
> at rest. If the chair/floor/whatever were not exerting a force
> opposite in direction to that of gravity, I would be in free fall.
> 
>> Now let's put another set of
>> bathroom scales under the chair. It is showing 110kg (the chair and
>> other scales are 10kg). So the chair is pushing up with 100kg to
>> balance you and down with 110kg. This chair is pushing both up and
>> down. 
> 
> The chair has always been pushing both up and down.
> 
>> How
>> does that work? Oh yes Newtons 3rd. Sorry, unlike in law you have to
>> describe what is happening, not just act and section.
> 
> It works quite simply.
> 
> The scale between me and the chair registers 980 newtons as always.
> Gravity pulls down my mass with a force of 980 newtons, and it pushes
> up with -980 newtons, for a net force of zero.
> 
> The scale between the floor and me, the chair, and the scale registers
> 1078 newtons. This is because the sum of the mass resting upon it (me,
> chair, and first scale) is 110 kilograms. At the same time, the floor
> pushes upon the scale with -1078 newtons, giving a net force of zero.
> 
>> Quite simply, it is the earth pushing "up" not the chair or more
>> accurately like Yumiko and me,mutal attraction.
> 
> No, it's really the chair, or balcony, or whatever you happening to be
> sitting or standing upon that pushes up on you. The fact that the
> earth's mass is the source of the acceleration of gravity does not
> mean that the earth is pushing up against you.
> 
>> You can actually find
>> this in Newton if you look closely but until Einstein, people just
>> sort of ignored it. Newton, himself, regardless of falling apples,
>> was not comfortable with gravity.
> 
> Comfort is irrelevant. The purpose of science is to describe the
> universe, not to make scientists comfortable.
> 
>>>> It's simple but you have to realise most of what you were taught at
>>>> highschool was wrong. First year university physics is mostly
>>>> relearning what you were taught at school.
>>> 
>>> 
>>> 
>>> I took college physics in high school by taking what is known as an
>>> "AP" class. I passed the exam at year's end and entered college with
>>> physics credit. Even in non-AP high school physics, I am pretty sure
>>> they teach SI units.
>> 
>> 
>> What has SI got to do with it?
> 
> See above links. A kilogram is a unit of mass, not force.
> 
>> It's my understanding that 1st university
>> in America is eqivalent to Year 12 of school (final year of
>> highschool) in Australia.
> 
> Yes, but it is also your understanding that a kilogram is a unit of
> force. 
> 
>>> Why did you mention Einstein when relativistic physics had nothing
>>> to do with your hypothetical? Was I traveling at 87% the speed of
>>> light? 
>>> 
>> 
>> I didn't mention relativistic physics at all. Einstein was
>> responsible for far more than relativistic physics.
> 
> Yes, but addes nothing to the physics being discussed here. A person
> sitting in a chair or a book resting on a table is sufficiently
> described with Newtonian physics.
> 
> (Did you get the 0.87c reference?)
> 
> - Kevin

There, please continue.