Flywheel / Inertia Effects

[clayliner]

I may be wrong, and it's a long time since I studied physics, but I suggest that it's inertia that would probably be greatest at low speed, not to say at rest. What increases with speed is, I think, the momentum.

David.

[Retiarius]

I may be wrong, and it's a long time since I studied physics, but I suggest that it's inertia that would probably be greatest at low speed, not to say at rest. What increases with speed is, I think, the momentum.

David.

You are correct:
Inertia - A property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.
Momentum - the quantity of motion of a moving body, measured as a product of its mass and velocity (including angular velocity i.e. rotational speed).

[Dave Cooper]

I must say I liked the sound of Leprechaun's clutch idea(s) until I remembered that my 009 line has quite a gradient coming up from the fiddle yard to the goods sidings /station. I was going to put a signal and refuelling depot part way up...

Yes, my '0' level physics 'says' - inertia (has a tendency to stay put, whether moving, or not). Momentum generally tends to keep things going (until something else intervenes).

However, one of my Christmas presents was an Arduino starter kit. Having read some of the 'capabilities blurb' of microcontrollers, I think it should be possible to apply a 'brake' to a clutched loco. This could be as crude as a micro servo lowering a peg down onto the track (to stop a runaway train on a grade) or, something bearing on the clutch /gearbox - both triggered by the loco coming to a stop.   

[Stefan Krebs]

Chaps,

I've got a problem here, which is: I'm not a native English speaker. I just spent a happy hour trying to get my head around your comments regarding inertia and momentum, and I can't.
Reason is that I can't tally the statement that inertia being a material property with my physics knowledge. To me inertia and momentum are physically the same thing observed in a different way, very much like centrifugal - and centripetal force?
Isn't it that both, inertia and momentum, are the same effect of mass, the first observed as the reluctance to change speed (vector and value!), the latter observed as impact?

Educate me, please!

Regarding the brakes on your train (clutched engines on slopes), there are 2 potential solutions, both with side effects:
1 .You can add axle mounted track wipers or electrical pick-ups to increase friction that holds your train on slopes. Downside: the engine has to work harder, and you're in trouble humping your train. Upside: cleaner tracks.
2, You can mount bristles in the track that 'catch' the train, be that  brush bristles vertically that catch the axle, or spring wires that 'clamp' the flange against the rail head. Downside: the engine has to work harder to pull the train through that track section; upside: you can still haul comparatively longer trains over the rest of the layout. Of course, installing a brake lever that engages and disengages the feature resolves the downside issue.
On second thought option 2 might be viable as a magnetic solution, which could be switched electrically.


Don't let me down, answers please!
Cheers
Waldschrat

[Retiarius]

From https://www.britannica.com/science/inertia
Inertia,  property of a body by virtue of which it opposes any agency that attempts to put it in motion or, if it is moving, to change the magnitude or direction of its velocity. Inertia is a passive property and does not enable a body to do anything except oppose such active agents as forces and torques. A moving body keeps moving not because of its inertia but only because of the absence of a force to slow it down, change its course, or speed it up.There are two numerical measures of the inertia of a body: its mass, which governs its resistance to the action of a force, and its moment of inertia about a specified axis, which measures its resistance to the action of a torque about the same axis. See Newton's laws of motion.
From https://www.britannica.com/science/momentum

Momentum,  product of the mass of a particle and its velocity. Momentum is a vector quantity; i.e., it has both magnitude and direction. Isaac Newton's second law of motion states that the time rate of change of momentum is equal to the force acting on the particle. See Newton's laws of motion.
From Newton's second law it follows that, if a constant force acts on a particle for a given time, the product of force and the time interval (the impulse) is equal to the change in the momentum. Conversely, the momentum of a particle is a measure of the time required for a constant force to bring it to rest.

Difference between Momentum and Inertia

Momentum	Inertia
Momentum is a vector quantity as it the tendency of a body to remain in motion.	Inertia is a scalar quantity as it is the resistance offered by the body to motion.
Momentum is denoted as 'p'.	Inertia is denoted as 'I'.
The momentum of a body of mass 'm' moving with a velocity of 'v' is calculated as p=m×v	The inertia cannot be calculated using a formula.
Linear momentum and angular momentum are the two types of momentum.	Inertia of rest, inertia of motion and inertia of direction are the three types of inertia.
Momentum depends on mass and velocity.	Inertia depends only on mass.
The total momentum is conserved.	Inertia has nothing to do with the conservation of energy.

The difference between between momentum and inertia should be understood clearly as these are an important topic in Physics.

[Dave Cooper]

To try to simplify things (hopefully, not over-simplifying), I have in mind a spinning gyroscope:

This, I believe, has both inertia and momentum. It also has "precession" if you try to disturb it's motion - it doesn't 'like it' ! I see this as a combined (side) effect of both inertia and momentum...

In the gliders that I fly, we have some instruments controlled by gyros. Left to their own devices, they will gradually 'wind down' and the instruments become misleading /dangerous - so, they have either electric motors, or, the moving airstream to keep them going. Hence, (little-by-little) inertia gets a "kick" and momentum gets a "boost". For aerobatics, we have to "cage" them, otherwise they 'topple' and become useless. Caging instantly kills both inertia and momentum as far as I can see. It works - otherwise there's an awful lot of planes up there about to crash !

(BTW all this ignores friction, stiction, angular momentum, fourth powers of moments of inertia and stuff that I should know but have forgotten how to calculate !)   

[Stefan Krebs]

Thanks for trying, but still confused. Especially bringing both explanations together. Any gyroscope is a gyroscope on a gyroscope, as in physical terms the earth is a giant gyroscope. That's why a gyroscopic compass works (and always points towards geographic North as opposed to magnetic North). All gyroscope when left to their own devices will eventually point to geographic North (as long as they are kept spinning.
And as we all have tried with our bicycle wheel: if I spin it and let go of the axle at one end it doesn't fall down, but rotates around the supported end of the axle. That's is caused by nutational forces, and is a result of inertia and momentum.
Inertia is a vector as it can only be observed on objects that are accelerated, which is a vector. And it manifests itself in the resistance to that acceleration vector, i.e. the force required to accelerate; be that either the vector direction or the scalar quantity.


Confusion reigns supreme; - I'm off to bed hoping for enlightenment in my dreams.

To be continued....; but can we stay we with the topic here please?


Cheers
Waldschrat

[Dave Cooper]

Oh dear ! Looks like my attempt at 'simplifying' has failed...

Let's try : spinning gyroscope is analogous to a spinning flywheel ie it wants to keep going until other things get in the way eg friction, air resistance etc.

A centrifugal clutch (even on 'tick-over') is a spinning flywheel (mass, velocity, inertia, momentum etc). As the motor spins up, the clutch engages, the 'flywheel effect' gains momentum, overcomes inertia and friction (partially) and the loco moves (accelerates).

Have a feeling I'm teaching my granny to suck eggs here, but, hopefully, we are back on topic !
Dave

[Stephen Rainsbury]

The difference between between momentum and inertia should be understood clearly as these are an important topic in Physics.

Trying to get people to understand that Momentum is not a force or energy is just as hard, we only briefly mention inertia and relate it to mass for both GCSE and A-Level. But that won't be my problem after July  8)
Stephen

[Hobby]

I recon Physics is like Pure Maths, you either "get it" or you don't with no in between! I am in the latter camp, this thread has been a "whoosh" moment!! :)

[Tom Haythornthwaite]

Things in motion have momentum.  Heavier or faster things have more momentum.  Real or model trains are only accelerated by application of power or by going down a hill, and only slowed by friction or climbing hills or running into things.  Trains with more momentum need more of these effects to achieve a given change of speed.  We use circuitry or software or judicious turning of the knob to make our model trains simulate having more momentum than they really do.  Sorted.

[Dave Cooper]

I recon Physics is like Pure Maths, you either "get it" or you don't with no in between! I am in the latter camp, this thread has been a "whoosh" moment!! :)

Last year I undertook a degree-level "math" course (on-line, via Caltech). We covered spherical trig' (ugh), analytical geometry (double-ugh), matrix algebra (triple-ugh) plus, some fairly 'hairy' calculus...

Yesterday, I watched a TV programme on "Quantum Disentanglement". I am now convinced I know nothing ! 

As for momentum and inertia in model railways - the electronic route seems the most sensible. Will I follow this path ? Probably not - no fun in solving a problem that has already been solved...

[Graeme Dunbar]

I remember having a tinplate car when I was about 6 or 7. It was battery operated and "remote controlled" in that steering was by Bowden cable. It used to pull away nicely and when I took it apart I found it had a miniature fluid flywheel in it. I could see that might work nicely in O gauge models, but not smaller.

Somewhere I have seen some very small centrifugal clutches, too big for 009, but still very small.

[Dave Cooper]

Hi Graeme

At about the same age as you were, I had 3 tinplate cars (Ferrari 250, Jaguar 120, Austin Healey 3000). I use to race them.

They had a rubber-covered friction wheel which engaged with the floor when you pressed down on the front bodywork. You then pulled back to (I imagine) wind up a clockwork drive. On release, each car would slowly accelerate up to speed - friction wheel doubled up as a flywheel /clutch ?

Must only have been around 10-15mm in diameter to fit in the cars so could fit in a loco cab I should think. Where are those toys now ?

[MickT]

Must only have been around 10-15mm in diameter to fit in the cars so could fit in a loco cab I should think. Where are those toys now ?

Those that didn't die of tin worm probably got trodden on and any that survived because the hapless children who owned them were not allowed to play with them as they "had to be kept in good condition" are probably in auction houses or lurking on eBay at outrageous "collector" prices!

Mick