8
   

Can an object be accelerating and yet -not- moving?

 
 
aspvenom
 
  1  
Reply Sat 16 Feb, 2013 11:00 pm
@maxdancona,
You're right.
It's been some time since I refreshed my knowledge on the physics course. Thanks for fixing that blatant error.
0 Replies
 
dalehileman
 
  1  
Reply Sat 16 Feb, 2013 11:01 pm
@Falco,
…the distinction between that something mathematically true and something intuitionally absurd. What we need to do is reduce the discussion to ordinary language in short sentences

I see the math aspect of aspect of reality as invention devoid of significant absolutes
0 Replies
 
dalehileman
 
  1  
Reply Sat 16 Feb, 2013 11:25 pm
@maxdancona,
Quote:
Do you understand or acknowledge that the slope of a line can be increasing even though, at that moment, it is (say) horizontal?
Intuition (mine) seems to ask how the position of an imaginary line could possibly apply to reverse in the direction of a massive object

Quote:
There are infinitely many points on the line between the present one and any nearby point, just as there are infinitely many moments in time between now and a second later.
Very interesting in terms of

http://www.google.ca/#hl=en&sugexp=les%3B&gs_rn=4&gs_ri=psy-ab&pq=universe%20proceeds%20in%20discrete%20jumps&cp=15&gs_id=7k&xhr=t&q=universe+change+in+discrete+jumps&es_nrs=true&pf=p&sclient=psy-ab&oq=universe+change+in+discrete+jumps&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.42661473,d.cGE&fp=1492e4e61bd751a1&biw=1283&bih=714


…but don't see how it applies

Quote:
How about a falling rock accelerating under the force of gravity. If it's velocity at some instant is (say) v, is it accelerating to a greater speed due to gravity ?
I suppose so

Quote:
All of modern mechanics is based on the observation that this is true. What difference is there if the initial velocity, v, is zero?
It seems a unique condition where if it isn't moving the acceleration is zero

Not math, not physics, Just Intuition
georgeob1
 
  1  
Reply Sat 16 Feb, 2013 11:49 pm
@dalehileman,
dalehileman wrote:


Even more interesting in that by your opwn declaration you're no physicist nor mathematician. I found the arguments in the link about granular time to be both without any detectable foundation (quantum mechancics doesn't require it) and nonsensical. Does your fabled intuition tell yoiu that there is no such thing as time????
RexRed
 
  1  
Reply Sun 17 Feb, 2013 12:48 am
It depends on what you measure the object in relation to... ie other objects or world coordinates. Certain secondary aspects of an object can accelerate while the core of the object seems to remains stationary. If you think of our solar system as a whole object the sun appears to remains stationary while parts of the sun (the planets) accelerate around it in orbits. So our solar system is an object accelerating yet not accelerating.

It is a fractal logic where it has levels of detail all accelerating at different rates; suns, planets, solar, systems, galaxies, all expanding around a central point that seems to be -not- moving...
georgeob1
 
  1  
Reply Sun 17 Feb, 2013 02:30 am
@RexRed,
The truth is much more complex than that. The hierarchy of motions you cited are not independent of each other. They influence each other, from large to small and are interconnected.

Newton's law applies relative to fixed, non accelerating coordinates only. In any rotating coordinate system, such as earth coordinates, corrections must be applied for the rotation of our planet. For the long-term movements of objects these corrections can be significant - even dominant. Even with this there are, as you suggest, additional factors due to the rotation of the earth around the sun, the rotation of the solar system around the center of our galaxy, and again of our galaxy around the gallactic cluster in which it resides. The relationships among these is not precisely fractical, but are nested as you noted. Happily, owing to the distances involved (1) from the sun to the earth (2) from the center of the galaxy to the sun, and (3) from the unknown center of our gallactic cluster to the center of our galaxy, etc. the angular velocities are vanishingly small, and it is sufficient for most human needs to consider only the effects of our rotating earth.

With this in mind Newton's law becomes Force = mass x acceleration, or

Force = mass x ( apparent acceleration in local coordinates - centrifugal force - Coriolis Force) where these fictitious forces are simply corrections resulting from the fact that earth coordinates are not fixed, but rotating with the earth.

centrifugal force can be thought of as the outward force on an object resulting from the earth's rotation. It is zero at the poles and a maximum at the equator. It is directed perpindicular to the earth's axis and therefore has components in the local vertical and in the northern hemisphere in a southerly direction.

Coriolis "force" is a bit more complex. Named after the French hydrodynamicist who first wrote about it, it is a correction associated with a body that is moving relative to the local (rotating) earth coordinates. It's magnitude is proportional to the local velocity of the object and to the angle between the direction of movement and the axis of the earth. Its effect is to turn moving objects to the right in the Northern Hemisphere and the left in the Southern. The atmospheric flow around low pressure areas is, as a result, counterclockwise in the northern hemisphers and the opposite in the South (same in your sink). Coriolis also affects oceran currents and is the reason we have westerly trade winds near the equator and westerlies at mid latitudes.
dalehileman
 
  1  
Reply Sun 17 Feb, 2013 01:01 pm
@georgeob1,
Quote:
Even more interesting in that by your opwn declaration you're no physicist nor mathematician.
Well thank you Geo but can't see how that could be interesting

Quote:
I found the arguments in the link about granular time to be both without any detectable foundation…...and nonsensical.
How can you describe a link to 23 million hits to be nonsensical

Of course if we can refer to the Whole Shebang (Her) as nonsensical, which many skeptics do, but then it includes your own assertions

Quote:
Does your fabled intuition tell yoiu that there is no such thing as time????
What gives you that notion

I was merely speculating, in effect, "…….wouldn't it be interesting if…."

But thank you Geo if it strikes you as "fabled"
0 Replies
 
RexRed
 
  1  
Reply Sun 17 Feb, 2013 02:17 pm
@georgeob1,
I like your assessment of Newtons force and acceleration observation and laws.

Also centrifugal (centrifical/centripetal) force is observed in objects accelerating along a course or inevitable path or spline.

Yet there are near and far away gravity forces and it seems at some point the physical is broken down by the quantum where forces and objects may obey other non-Newtonian laws.

For instance an object may be able to accelerate yet remain still.

In acting and stage we call this "emoting". Where you may walk on stage with a dead-pan look on your face but inside "emotionally" you are accelerating and charged at the highest level possible.

Our sun seems to be in that phase of high acceleration while it appears to remain in a static location. There must be other external quantum dark energy forces causing the sun to accelerate while appearing static.

I think that physical laws do not follow perfectly down the rabbit hole due to object orientation.

The sun may be effected greatly by a distant object while the planets around the sun are unaffected by this distant force.

Thus quantum force is not always relative and the physical laws can defy force and also possibly create force and acceleration out of seemingly nothing.
RexRed
 
  1  
Reply Tue 19 Feb, 2013 12:58 am
~Cassini sheds light on cosmic particle accelerators

19 February 2013

During a chance encounter with an unusually strong blast of solar wind arriving at Saturn, the international Cassini spacecraft detected particles being accelerated to ultra-high energies, similar to the acceleration that takes place around supernova explosions.

Shock waves are commonplace in the Universe, for example in the aftermath of a stellar explosion as debris accelerates outwards in a supernova remnant, or when the flow of particles from the Sun – the solar wind – impinges on the magnetic field of a planet to form a bow shock.

Under certain magnetic field orientations and depending on the strength of the shock, particles can be accelerated to close to the speed of light at these boundaries. Indeed, very strong shocks at young supernova remnants are known to boost electrons to ultra-relativistic energies, and may be the dominant source of cosmic rays, high-energy particles that pervade our Galaxy.

Space telescopes reveal evidence for accelerated electrons at supernova remnant shocks as X-ray emission, but these observations are made at great distances and thus the orientation of the local magnetic field can only be poorly measured at best. Without this crucial information, it is difficult to gain a full understanding of the shock acceleration process.

Scientists want to understand how the acceleration of electrons in very strong shocks with large ‘Mach numbers’ depends on the angle between the magnetic field and a vector at right angles to the shock front. In particular, they are interested in what happens in a ‘quasi-parallel’ shock, where the field and vector are almost aligned, as may be found in supernova remnants.

http://www.esa.int/Our_Activities/Space_Science/Cassini_sheds_light_on_cosmic_particle_accelerators

https://sphotos-a.xx.fbcdn.net/hphotos-ash3/563126_427477674001597_192698057_n.jpg
0 Replies
 
dalehileman
 
  1  
Reply Tue 19 Feb, 2013 10:12 am
@RexRed,
Quote:
For instance an object may be able to accelerate yet remain still.
Rex this one still has me going, unless the acceleration is caused by a passing gravitational field. That is, if the pilot fires up his rockets in order to remain still


Quote:
The sun may be effected greatly by a distant object while the planets around the sun are unaffected by this distant force.
Really an interesting speculation Rex but would this be true if our entire system were accelerating even slightly as a result of that force
engineer
 
  2  
Reply Tue 19 Feb, 2013 12:22 pm
@dalehileman,
dalehileman wrote:

Quote:
For instance an object may be able to accelerate yet remain still.
Rex this one still has me going, unless the acceleration is caused by a passing gravitational field. That is, if the pilot fires up his rockets in order to remain still

A still object cannot accelerate and remain still. Acceleration is the rate of change of velocity over time so a still object that is accelerating will start to move. If a pilot is using his rockets in order to remain still, he is not accelerating, he is using his rockets to counter another force (likely gravity) so that the net force on his ship is zero.
dalehileman
 
  1  
Reply Tue 19 Feb, 2013 12:35 pm
@engineer,
Quote:
a still object that is accelerating will start to move.
Forgive me Eng, lacking some sort of technical vocabulary with which I'm unfamiliar, that statement intuitively sounds absolutely contradictory

…though I think I understand what you mean. From a purely mathematical point of view, if an object reverses its direction, in that infinitesimal moment it is still accelerating. It's just that Intuition finds the concept troubling

Quote:
…...he is using his rockets to counter another force (likely gravity) so that the net force on his ship is zero.
Yes, I agree I was wrong on that score anyway
dalehileman
 
  1  
Reply Tue 19 Feb, 2013 01:08 pm
@dalehileman,
Again a2k cut me off in the middle of a thought; I guessI should be grateful it wasn't the middle of a sentence

Yes, I see what you mean: I consider myself stationary in my ship out there in space but when the object approaches I'm drawn to it so I feel acceleration, at which moment the Earthling however sees me coming at him even faster. But when I fire my rocket so as to resume motionlessness the feeling vanishes

Of course for only a microsecond or two before I "touch" down
0 Replies
 
maxdancona
 
  1  
Reply Wed 20 Feb, 2013 07:24 am
@dalehileman,
Quote:
a still object that is accelerating will start to move.
Forgive me Eng, lacking some sort of technical vocabulary with which I'm unfamiliar, that statement intuitively sounds absolutely contradictory


Dale, this is really simple if you start using logic instead of intuition.

Acceleration is a change in velocity.
An object that is "starting to move" goes from zero velocity to some velocity.
There is no way to go from zero velocity to some velocity without a change in velocity.
By definition, "start to move" means acceleration.

How can we get you to abandon your flawed intuition?
dalehileman
 
  1  
Reply Wed 20 Feb, 2013 12:18 pm
@maxdancona,
Quote:
How can we get you to abandon your flawed intuition?
By murdering me

How can it be accelerating before it starts to move
Thus by your definition a stationary object is always accelerating

Yes I know, the math supports your contention but math is merely the circulation of electrons in brain tissue
maxdancona
 
  1  
Reply Wed 20 Feb, 2013 02:19 pm
@dalehileman,
Quote:
How can it be accelerating before it starts to move
Thus by your definition a stationary object is always accelerating


No. Let's try this again.

The definition of "acceleration" is "changing velocity".

During any (non-zero) period of time that an object is stationary it's velocity starts at zero, and ends at zero. That means no change in velocity. Which in turns means no acceleration.

During any (non-zero) period of time that an object "starts to move", it's velocity starts at zero, and ends at not zero. That means there is a change in velocity. Which in turn means there is an acceleration.

The logic here is very simple.

dalehileman
 
  1  
Reply Wed 20 Feb, 2013 02:33 pm
@maxdancona,
Quote:
The logic here is very simple.
I understand the logic, that acceleration starts at zero but yet "a still object that is accelerating" somehow sticks in the craw of the Intuition (mine of course)

Thank you however for your heroic attempt at clarification
engineer
 
  2  
Reply Wed 20 Feb, 2013 03:48 pm
@dalehileman,
Would it help if I told you that humans don't intuitively understand certain things? Understanding position is very straightforward. It is in that direction, three meters away. Understanding velocity is a little harder. It is fast or slow, but you don't intuitively know how fast. You might need to compare it to something you know. If you see a car going past you might not be able to guess its speed with any accuracy but if you are going 50kph and it eases by you your intuition might tell you it's doing 55. Now think about acceleration - the rate of change of velocity. If you weren't able to intuitively generate a velocity number, how could you possibly figure out the rate at which it is changing? You'd have to watch it for a while to even have a chance and you'd probably still be wrong. Acceleration just doesn't lend itself to intuition. Your brain just isn't wired the right way.
dalehileman
 
  1  
Reply Wed 20 Feb, 2013 04:16 pm
@engineer,
Quote:
Would it help if I told you that humans don't intuitively understand certain things?
I've been trying to beat mine down but it's very stubborn

Quote:
Understanding position is very straightforward…...You might need to compare it to something you know…...Understanding velocity is a little harder……..
All right

Quote:
Now think about acceleration - the rate of change of velocity.
Yes maybe tougher. But what really tweaks, is not so much idea that it starts at zero but that it's presumably it's accelerating before it starts moving

Quote:
If you weren't able to intuitively generate a velocity number, how could you possibly figure out the rate at which it is changing?
Sorry forgive me Eng but I don't see how this bears on the issue. Alas, apparently nobody else is much interested. Maybe the issue is moot, or purely semantic like freewill

Quote:
…….Your brain just isn't wired the right way.
That could well be
maxdancona
 
  1  
Reply Wed 20 Feb, 2013 09:19 pm
@dalehileman,
The point is that in understanding thing such as this, intuition is worse than useless. It is making it difficult for you to "accept" something that is logically simple.

My advice is to ignore your intuition in almost any case. The one exception is when making a quick decision is more important than making a correct decision.

There is an evolutionary reason for intuition. If you are a small mammal being attacked by a flying predator, acting quickly without thought has a survival value. But if you are an advanced mammal whose goal is understanding math and science, intuition is worse than useless.

Your intuition is wrong. Just ignore it.
 

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