One for Olmy and STA?

[carnyx]

Having stirred up a lot of fun with the 'Time' question, it is clear that Olmy and STA like to see things from a mathematical perspective, so here is something for them to ponder.

All cyclists and other travellers know that a steady force applied to a mass produces an acceleration, which results in an ever-increasing speed, which produces in turn an ever-increasing distance travelled. When the force is removed, the acceleration stops, and the speed stops increasing, and the distance carries on increasing at this rate.To reverse this process we need to apply an opposite force, which produces an opposite acceleration, and we see the speed decline and the mass will come to a stop. As the speed then builds up in the opposite direction the distance decreases until we are approaching the starting point. We will then have to apply the force in the original direction, which will cause an acceleration, and the speed will steadily decline until the mass stops moving.

The handy formulae for quantising this process (i.e the recipe for producing results based on different inputs) is

acceleration = force/mass

velocity = acceleration x time

distance = velocity x time

As you see there are two integration steps involved.

But I know of a simple entirely mechanical apparatus, where the velocity of the mass is directly proportional to the force applied. You could make one yourself.

When a force is applied, the mass moves at a steady rate. If the force is increased the mass moves faster, and when the force is removed the mass stops moving.

i.e;

velocity = force/mass

A whole integration step has been removed. The mass appears to have no momentum, and so no kinetic energy. Yet it clearly has mass, and must therefore accelerate. What kind of mass accelerates instantaneously? Doesn't it require infinite force?

What on earth is going on, and can a study of those well-known formulae provide an explanation?

[principled]

But I know of a simple entirely mechanical apparatus, where the velocity of the mass is directly proportional to the force applied. You could make one yourself.

When a force is applied, the mass moves at a steady rate. If the force is increased the mass moves faster, and when the force is removed the mass stops moving.

i.e;

velocity = force/mass

I'm confused. For the mass to go from moving to not moving or vice versa there must have been some acceleration/deceleration or are you suggesting that a body goes from rest to x velocity without any change of velocity wrt time? That's a novel concept. Please explain.
P

[carnyx]

principled

Thank you for showing a compete understanting of Post 1. .. (which is more than olmy can manage, apparently, but we'l let that pass)

Yes, you are right. But it is a puzzle, and needs some counterintuitive thinking, and hopefully posters will join in discussing it as a group.

And so I'll save putting forward explanations of my own, until later.

[mightydrunken]

Hi carnyx, could you describe the system you are talking about? Otherwise it is impossible to give a clear answer to what is going on.
For something with mass to accelerate instantaneously would require infinite force.

[carnyx]

mightydrunken #3

Best I can do at this early stage is to repeat the 'recipe', with emphases;

But I know of a simple entirely mechanical apparatus, where the velocity of the mass is directly proportional to the force applied.

You could make one yourself.When a force is applied, the mass moves at a steady rate. If the force is increased the mass moves faster, and when the force is removed the mass stops moving....


......The mass appears to have no momentum

And you can apply the force with your finger, and then see the mass take up a velocity which is directly proportional to your finger pressure.

[speakertoanimals]

What on earth is going on, and can a study of those well-known formulae provide an explanation?

What is going on? Just that some people have little or no understanding of physics. Just because you can construct an apparatus (i.e. objects other than your finger and the weight being pushed), so that the effect of pushing the weight SEEMS to be contrary to Newtons laws doesn't mean that it is -- just means that you have neglected to include the apparatus in your analysis, and hence not included all forces and all momentum, hence you are talking bollocks.

For example, we could consider a fluid where the viscous force depended on the velocity. Then for a fixed push, and a small object, the terminal velocity of the object depends on the applied force. And if you stop pushing, the object quickly comes to rest.

Newton is wrong? No, just that you have forgotten to include the kinetic and probably elastic energy of the fluid in your analysis (and I could add heat and sound energy if we are thinking of terminal velocity in air).

In fact, you could come up with various weird and wonderful fluids (and some of them actually exist), because turns out that simple Newtonian fluids are a very special case.

But you have to be really daft to think any of this offers any challenge to Newtons laws, or shows anything other than -- the simple first examples you do are just that -- simple.

If you think this is maths, you need to try harder....................

[carnyx]

@sta #5

" a simple entirely mechanical apparatus" seemed to me to have excluded liquids, including thixotropic stuff, greases, glues, gases, and the like.

I suppose I should have said that it is made from solid parts, in any reasonably equipped workshop Metal of any kind would be OK .. and you could even make it out of wood ... or plastic I suppose . A glass one would be pretty.


And, does the rest of your reaction indicate that you find this puzzle somehow existentially offensive.

Are you a teacher, too?


Come on, STA, could you produce a design that would do the job? That would SEEM to be contrary to Newtons laws .

All the mathematical formulae already exist ...!

Try again.

[Progenitor A]

Well it's beyond me Carnyx - any further clues?

[carnyx]

@nm

It seems that torque-induced precession is not as well-known as it ought to be.

The thing is, that applying a force to a gyro gimbal will cause the gyro to precess at a velocity which is directly proportional to the weight. Remove the force, and the gyro will stop.

Thus it appears as if the apparatus has no inertia, and also that f=v

The video of the first sequence of this famous lecture shows the phenomenon.

And, I strongly recommend clicking to download chapter 4 of "Engineer through the Looking Glass" for a much more detailed discussion.

www.gyroscopes.org/1974lecture.asp

[Progenitor A]

Ah good point!
Just what is the explanation of a rotating disc weighing less than a stationary disc? Does the spinning disc create some sort of aerodynamic lift?

And apparently infinite acceleration/deceleration?

A big, big puzzle to me

But wasn't Laithwaite ostracised by the scientific community for his espousal of these mysteries?

Suppose, then ther must be a reasonable scientific explanation

[mak2]

It is an interesting topic. I think the clue is in a slightly misleading statement in the original message.

..when the force is removed the mass stops moving.

Mass is always moving, although the centre of mass may stop moving.

[carnyx]

Progenitor A,

The point of the puzzle was to show that the mathematics is not the only eyepiece through which physics is to be percieved, despite what STA, olmy and eammon seem to be claiming.

The mathematical formulae that 'explain' this aspect of gyroscopic behaviour indeed do exist, and they are fearsome. However, the mastery of the ingenous intricacies of these formulae cannot reveal one single instance of the 'counter-intuitive thinking' (aka creativity) extolled by olmy. So QED, as it were.

It is as if the very notion of the novel has been frozen, and trapped inside these equations. And via those academic-scientists such as STA, the only 'progress' to be made is up the scaffolding of formulae rather than through the observation and consideration of real-word phenomena themselves. The practice of Virtual physics as opposed to Real physics.

In this meta-mathematical world of meta-physics, all is Orthodoxy, and its politics bears a remarkable similarity to those mediaeval religious hierarchies where the observations of real, physical events were perceived as an existential threat.

Anyway, here is a really amusing video;

www.youtube.com/watch?v=8H98BgRzpOM

[Progenitor A]

Hi Carnyx
Is there an explanation without using maths that explains the apparent weight-diference when the disc is spinning? I find this fascinating.

[speakertoanimals]

The point of the puzzle was to show that the mathematics is not the only eyepiece through which physics is to be percieved, despite what STA, olmy and eammon seem to be claiming.

Except the very lack of intuition when it comes to gyroscopes and rotatory motion show just why we need to do it using maths, especially when our intuition fails.

And it is just this total lack of intuition that makes gyros SEEM so mysterious, and why so many find the pseudoscience based around gyros so fascinating.

Except they aren't in the least mysterious, Newtons laws apply perfectly well to them as they do to falling rocks.

As regards precession, you'll get daft answers (and never understand it) if you try and use Newtons equations for linear motion (F=ma), rather than the equations for rotatory motion. I might also add that most elementary treatments of this problem neglect the angular momentum due to the precessional motion, considering just the angular momentum of the rotor, hence not totally correct which can lead to seeming inconsistencies.

[Progenitor A]

Thanks STA
As usual you have said, in many words, absolutely nothing.

No, no plesae do not attempt to explain

Your performance with gravitational potential is enough to put anyone off science for a lidfteim.

Do you like that?

Causing the inquisitive innocent to FO?