How forces work
From: Kevin Gowen (kgowenNOSPAM_at_myfastmail.com)
Date: 03/09/05
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Date: Tue, 08 Mar 2005 20:35:05 -0500
Ron Hitler Barrassi wrote:
>
>
> Kevin Gowen wrote:
>
>> Ron Hitler Barrassi wrote:
>>
>>>
>>>
>>> Kevin Gowen wrote:
>>>
>>>> Ron Hitler Barrassi wrote:
>>>>> Seems you have "forgotten" your chair example which means you have
>>>>> realised you were wrong.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> What's to forget? I'll repeat it again:
>>>> If a person with a mass of 100kg is sitting on a chair at rest, the
>>>> force of gravity's pull is 980 newtons. In turn, the chair pushes up
>>>> with 980 newtons.
>>>
>>>
>>>
>>>
>>> No. You still think that gravitational force is a "downward" force.
>>
>>
>>
>> I, like most people, tend to think of the earth's center of mass as
>> "down".
>
>
> I refer you to Newton's Law of Gravity.
Is that the one where "m" is mass in grams?
>>> Read Newtons Law of Gravitation, (ignoring General Relativity) it is
>>> a mutal force of attraction.
>>
>>
>>
>> Even a stopped clock is right twice a day.
>>
>>> Earth is pushing up.
>>
>>
>>
>> I thought it was attraction, not repulsion.
>
>
> There is a difference between attraction forces and replusion forces?
You can confirm this empirically. Jump off a tall building. First you
will feel an attractive force, followed by a repulsive force.
Could you explain some more about this mystical action-at-a-distance
force through which the earth pushes masses away from it?
>> No, the chair is pushing up. That you insist otherwise illustrates
>> that you do not understand what force is.
>>
>>>> What on earth did you mean when you said "g=1"? What are the units?
>>>>
>>>
>>> I meant 1g. Yes, I was careless.
>>
>>
>>
>> I see, so you meant to say g=1g? Alrighty then.
So what did you mean when you said g=1?
>> Funny, the last time I said that, you made a wise crack about how we
>> would lose a lot of springs that way because they would be
>> accelerating off into infinity. That was also around the time that you
>> said that a spring could not be used to measure a force, even though
>> that is precisely how many forcemeters work.
>
>
> A spring cannot measure one force. It can only measure two forces.
> Action and reaction. You went off on a semantics.
Yes, a spring can measure two forces. That is how it can be used to
measure weight.
>>>>> How does a chair magically know when to push up?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> The chair knows nothing. It doesn't need to.
>>>>
>>>>> If you add two
>>>>> equal and opposite forces they cancel each other;
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Yes, which is why the person is at rest.
>>>
>>>
>>>
>>>
>>> (maybe I have to introduce time dilation)
>>
>>
>>
>> Maybe you have to learn about what a force is.
>
>
> one, two.
There's an improvement. I wonder when you'll learn the next number.
>>>>> so why does the chair push down? (down being the null length vector
>>>>> pointing to the center of the earth)
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Push down on what, the earth? Probably because it has mass.
>>>
>>>
>>>
>>>
>>> As we have discussed previously it is now pushing down with a force
>>> of it's own weight and yours. It doesn't seem to be pushing up at all.
>>
>>
>>
>> Sure it is pushing up. It is pushing up with the same force as my weight.
>
>
> which you can't measure.
No, if it exists, it can be measured.
>>>>> | 980newtons
>>>>> \|/
>>>>>
>>>>> /|\
>>>>> | 980newtons
>>>>>
>>>>>
>>>>> so we have fab - fba = 0. But yet the chair still pushes down with
>>>>> a force 980newtons. Seems your highschool idea of physic is missing
>>>>> something significant.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Maybe you should enlighten me, then.
>>>
>>>
>>>
>>>
>>> Replace the chair with a spring and it's obvious. You and the earth
>>> are compressing that spring. That pop sound is the sound of the
>>> cartoon light coming on.
>>
>>
>>
>> Sorry, no light. I have no idea what you are attempting to explain.
>> The chair is only pushing down with 980 newtons if it is massless.
>
>
> That was an explicit assumption you happilyy accepted earlier.
What is "that"?
>> I am glad to see that you realize that a 100kg mass on the surface of
>> the earth is pulled down with a force of 980 newtons. Much better than
>> your assertion that a 200kg mass was pulled down with 400 newtons of
>> force.
>
>
> Except for when you lifted it. F=ma.
Maybe you should show us the numbers you are plugging in there to arrive
at your answer.
> "You pick it up and momentarily there is 400kg [3920N] pushing downo on
> the chair (you + the bag + the acceleration of lifting the bag)"
No. Again, since I am not traveling at .866c, we don't have 200kg
magically appearing out of nowhere.
It is nice to see that you realized the acceleration of gravity is more
than 2 m/s^2. When you said that a mass of 200kg would have a weight of
400 newtons, that really brought teh laffo.
> Have you forgotten that when you used to weigh your self the scales
> would indicate very high weights initially? Can't have been that long ago.
How could that be? After all, according to you, a scale does not measure
force.
>>> A few key points:
>>>
>>> Special Relativity: speed of light, observers agree, speed distorts
>>> time etc (ignores gravity)
>>>
>>> General Relavitity: (Einstein's theory of Gravity) mass curves
>>> time/space, gravity bends light, corrects Newton etc.
>>>
>>> I am refering to the time dilation of mass (Gen Rel) which accounts
>>> for gravity in "normal" situations, not from speed (Spec Rel). "c"
>>> has nothing to do with it.
>>
>>
>>
>> I see. You did some Googling after the whooshing. Good on you, as you
>> Commonwealth folk say.
>
>
> You think I had to google for that?
Or you skimmed through A Brief History of Time, or perhaps The Physics
of Star Trek. I can think nothing else, as your persistence in confusing
force with work labels you a scientific ignoramus.
> You are projecting again. Admit it
> Gowen, you had no idea what General Relativity is. I hope you do now.
Yes, I had no idea what it was.
> 5en:
> "Why did you mention Einstein when relativistic physics had nothing to
> do with your hypothetical? Was I traveling at 87% the speed of light? "
Yes, I said that because you magically added 200kg to the system. What
other explanation could there be?
>> By the way, I hope you aren't under the impression that relativistic
>> physics is more advanced than Newtonian physics.
>
>
> Advanced? No it is simpler, but it required non-Euclidian geometry.
Actually, it's not simpler, either. Science is not like technology. No
branch is more or less advanced than another.
> Maybe you should jump Newton and go directly to Einstein. Tensors
> shouldn't be a problem for you.
Given your ignorance as to what a force is, I question your ability to
determine the difficulty level of other concepts.
This page is your only hope:
http://www.physicsclassroom.com/Class/circles/U6L4d.html
Start reading at the part that has a cartoon of a man sitting in a chair.
-- FAB = -FBA It's not just a good idea; it's the law.
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