Heater
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Mon Jun 04, 2018 11:21 pm

davidcoton,

We were discussing rotation and acceleration, and which causes which. Your statement was that "The rotation does not cause acceleration. Acceleration causes rotation."

Well, let's see. According to our hero Newton we have a formula for that. The magnitude of the centripetal acceleration is related to the tangential speed and angular velocity as follows:

a = v^2 / r = ω^2 r

Written that way it looks like the rotation ω is causing the acceleration. Increase ω and a increases.

But we can quite validly rewrite that equation as:

ω = root(a / r)

Now it looks like the acceleration is causing the rotation. Increase a and ω increases.

Hmmm...this looks like a chicken and egg problem. Which causes which?

I'm not sure why you insist that one is the cause and the other is the effect.

I think "causes" is the wrong way to look at it. The rotation and the acceleration are in balance. As the equation describes. That is what equations are, a balance between one side and the other.

We could consider an even simpler example by way of analogy. Say two equal masses, m1 and m2, resting on the pans of some scales in balance. Your claim above is like saying that m1 does not fall down because m2 is holding it up. Another might say, m2 does not fall down because m1 is holding it up.

I say, it's a stable system. Both m1 and m2 stop each other from falling down. Take away either and the other falls down.

So it is with centripetal acceleration and rotation.

drgeoff
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 12:21 pm

Consider a spacecraft about to undertake a slingshot around a planet. It is travelling in a straight(ish) line. It approaches the planet whose gravitational pull makes the craft accelerate towards the planet. The trajectory is now rotational. Isn't that a clear case of acceleration causing rotation?

(Get the approach line and speed just right and the craft will go into orbit around the planet.)

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Burngate
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 3:34 pm

drgeoff wrote:
Tue Jun 05, 2018 12:21 pm
(Get the approach line and speed just right and the craft will go into orbit around the planet.)
Will it?
Or put it another way - reverse everything - if a craft is in orbit, can it be ejected from that orbit without a third body?

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davidcoton
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 5:23 pm

Heater wrote:
Mon Jun 04, 2018 11:21 pm
davidcoton,

We were discussing rotation and acceleration, and which causes which. Your statement was that "The rotation does not cause acceleration. Acceleration causes rotation."

Well, let's see. According to our hero Newton we have a formula for that. The magnitude of the centripetal acceleration is related to the tangential speed and angular velocity as follows:

a = v^2 / r = ω^2 r

Written that way it looks like the rotation ω is causing the acceleration. Increase ω and a increases.

But we can quite validly rewrite that equation as:

ω = root(a / r)

Now it looks like the acceleration is causing the rotation. Increase a and ω increases.

Hmmm...this looks like a chicken and egg problem. Which causes which?

I'm not sure why you insist that one is the cause and the other is the effect.
Because, if the body were in the same place but not rotating, it would still accelerate.
The reverse is not true. If the body were rotating but not accelerating, it would cease to rotate.
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Heater
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 7:55 pm

davidcoton,
Because, if the body were in the same place but not rotating, it would still accelerate.
How so? Two stationary masses attached to the ends of a solid rod, not rotating or subject to external forces, do not accelerate any were. They just sit there.

Give that rod and mass system a spin and now we have centripetal acceleration and rotation going on. As per Newton's equations above. As we watch it spin it's impossible to say the acceleration causes the rotation or vice versa. It makes no sense to ask.

Grab hold of that rod and masses assembly, stop it rotating, there is no more acceleration going on.

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davidcoton
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 8:20 pm

Heater wrote:Give that rod and mass system a spin
What is involved in that? No less or more than applying a force, thus accelerating the mass into a rotational path. Resolve the applied force and you will end up with the centripetal component.

Think about the planet and satellite model and it becomes even more obvious. Stop the rotation by firing a rocket to reduce the tangential component of velocity (ie, reduce the spin), and the gravitational force is unaffected.Satelite orbit decays. Increase the spin by increasing the tangential velocity, the acceleration due to gravity is unaffected, so the satellite increases its distance from the planet.

Perhaps you should suggest to the Tranquility Project people that, if instead of going into orbit, just going up without any rotation would stop the downwards acceleration, so the cost of fuel to get to the moon would be trivial.
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Imperf3kt
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 10:07 pm

The only thing rotating here is my head, this discussion has strayed so far from the title its not even clear how we got here.
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MaxTheSpy
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 10:14 pm

Imperf3kt wrote:
Tue Jun 05, 2018 10:07 pm
The only thing rotating here is my head, this discussion has strayed so far from the title its not even clear how we got here.
Stick around and Ill show you just how far this rabbit hole goes.
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davidcoton
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 10:32 pm

MaxTheSpy wrote:
Tue Jun 05, 2018 10:14 pm
Imperf3kt wrote:
Tue Jun 05, 2018 10:07 pm
The only thing rotating here is my head, this discussion has strayed so far from the title its not even clear how we got here.
Stick around and Ill show you just how far this rabbit hole goes.
It's not a rabbit hole, it's a freak wormhole in the fabric of the space-time continuum.
"Thanks for saving my life." See https://www.raspberrypi.org/forums/viewtopic.php?p=1327656#p1327656
“Raspberry Pi is a trademark of the Raspberry Pi Foundation”

Heater
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Re: What If I Told You... You could have a bad to the box Matrix Pi

Tue Jun 05, 2018 10:55 pm

Imperf3kt,
The only thing rotating here is my head, this discussion has strayed so far from the title its not even clear how we got here.
The thread has not strayed far at all. We are discussing The Matrix. Some people see it one way, others see it another way.

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