Re: The mechanism behind bouncing...


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:g99as2pkr9ugvcobb2r7upq2ck7f50v71j@xxxxxxxxxx
On Sat, 03 Feb 2007 08:13:46 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:


"KILOWATT" <kilowatt"nospam"@softhome.net> wrote in message
news:45c3aa6d$0$31564$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Hi... thanks for your attention.

I just wish to know the precise reason why for example, a digital
counter
may count many pulses on it's clock input when the clock is feed via a
non
noise-free source like a mechanical switch. It is because when the
contacts
makes/breaks, arcing (i've read somewhere that there can be a
possibility
of
arcing even at low voltage) occurs, or if it's because of the very rough
surface (microscopically-speaking) of the switch contacts, were the
metal
molecules grinds (and possibly flexes) together, during switch
activation?
TIA for your reply.



The atoms of the two materials are not configured in such a way that there
is complete contact.

---
That's not true.

When the contacts come to rest after the bouncing period is over
they will either be in intimate contact or they will be completely
separated.
---

If they were then the materials would be fused.

---
Which, indeed, they are until the coil is de-energized and the
return spring exerts force on the armature, breaking the microscopic
weld(s) and allowing the contacts to open.
---

So can you shear a part a solid piece of metal with a spring? Its a matter
of degree. If the contact interface was completely "fused" then thee would
not be any contact interface(assuming the same material is used for both
contacts).


Since there are not fused and they slide there is friction involved
and this friction causes the contacts to move farther a part and then
closer together.

---
No. The friction you're talking about is only about the contacts
rubbing against each other when they're making or breaking and is a
second order phenomenon compared to bounce, which occurs when the
contacts alternately make and break when the coil is energized.
Bounce also occurs when the armature is de-energized, but to a
lesser degree, and is caused by the moving contact skipping across
the stationary contact when the coil is de-energized.
---

The friction is due to electrical forces. There are only 4 known
forces(well, 4 main ones) in the world. Gravitations, Electrical, Strong and
weak. Gravitational is like 10^(-40) smaller than electrical. The strong
and weak work only as a sub-atomic level.

So are you saying there is some other forces involved?


So the average distance between the constants is changing
significantly campared to when is not moving and they are making good
contact. So now the electric field is changing because of the distances
changing between the contacts. As the contacts move farther away the field
becomes weaker but now we have a capacitive effect. This effect creates a
force between the contacts that attract them. One now has a kinematic
force
pulling the contacts away(so it can slide), one of friction that wants to
stop the slide, and one of capacitance that is attractive(I'm sure there
are
more too).

---
No. The high-level bouncing behavior is due only to the gross
mechanical characteristics of the contacts and has vanishingly
little to do with the microscopic effects, which are at least six
orders of magnitude smaller than the mechanical effects, I'd guess.


Sure, but we are not talking about high level. The high level is strictly
due to the averging of the microscopic. See above about the forces.

Do you have some hard numbers which would prove otherwise?


Yes I do. 4 forces, 1 is too weak to be of any use for this problem, the
other 2 are too weak at the distances we are discussing.

Here, I'll even get you a link with some pretty pictures:

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html

How do you explain yourself out of this one? Just cause you have a quarter
doesn't mean the quarter is smallest denomination. (Ok, stupid analogy but
works).

All of reality is based on these 4 forces(at the present understanding of
reality). You can ignore that fact and just look at the infituide of
outcomes that these forces produce but you are then neglecting what really
happens. Its even much more complicated than this but these are adaquate for
the OP's problem. He asked what was happening at this level and these are
the tools one has to use to explain it. You cannot explain something at a
lower level higher level tools(ok, maybe a little but theres no guarantee
that it will work).



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