Re: The mechanism behind bouncing...


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:fr4cs21bmjbj0l0p4dq9mtr4cpn757i09t@xxxxxxxxxx
On Sun, 04 Feb 2007 14:25:19 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:


"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:

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?

---
Yes.
---


I'd like to see that.

Its a matter of degree.

---
Of course. Have you ever seen how a set of contacts is made?

Usually one contact is flat and the other rounded (or they're both
rounded) so that when they're in contact with each other only a
very small area of metal is involved in making the contact.


That way, when the contacts bounce and microscopic welds are made
between the contacts, the spring will have the strength to break the
welds and open the contacts.
---


Yes, but this is explained in a microscopic way.

If the contact interface was completely "fused" then thee would
not be any contact interface(assuming the same material is used for both
contacts).

---
It doesn't make any difference if the metals are dissimilar or not,
at the weld there is no "interface".
---


Sure it does. Sheesh. Do you remember in physics when doing experiements
with friction? You would slide different materials along a flat surface and
measure there coefficient of friction? Did you ever remember reading about
the case when the two materials were the same? (if they were perfectly
clean then they could stick together much easier than different materials).

This is due to the crystal structure of metals. You don't have this if the
metals are different.

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.

---
http://en.wikipedia.org/wiki/Friction
---


Not sure wha tyour getting at:

It is not, however, a fundamental force, as it originates from the
electromagnetic forces and exchange force between atoms.

The key is originates. It means that it can be "explained" in terms of the
fundamental forces(which there are only 4 so essentially everything can be
explained in terms of that).

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?

---
Nope, but I'm talking at the macro level where when two materials
are pressed together more and more tightly it becomes more and more
difficult to slide them past each other.
---


Yes, but how can you even talk about that? You act like the macroscopic
level is something totally different some the microscopic. The macroscopic
is just a manifestation of the microscopic. If you want to talk in those
terms then thats fine. But then we are talking about different things.
Although since the macroscopic is derived from the large scale microscopic
my ideas should, if correct, explain the macroscopic in a much more detailed
way.

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.

---
I am, because that's all that's needed to describe contact bounce in
response to the OP's question.
---


Well, here we have to disagree. Since the OP talked about the microscopic
effect of "friction"(and by the wiki page is the EM and interatomic forces)
then I assumed he ment at the microscopic level.

The high level is strictly
due to the averging of the microscopic.

---
Yes, but so what?

What the OP wanted to know about was what caused the false count and
I can assure you that the electrostatic attraction or repulsion of
the contacts has nothing to do with it. It's merely the contacts
making and breaking repeatedly until they settle down, and that's
caused by a movable mass on the end of a spring bouncing against a
fixed mass.
---


Yes, that is true. BUT he asked why in terms of the micrscopic. He did not
asked why in terms of the macroscopic level. I already pointed out the
quote.

See above about the forces.

---
Poppy***.
---


Ok, you don't have to believe me...

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?

---
The electromagnetic forces are also too weak to account for contact
bounce, which is purely mechanical.


Ok John. All I can say is that we'll have to disagree. I believe you are
wrong here. (in the above statement).

My only logic evidence I can give you is that:

Physics as described 4 fundamental forces. These forces as the only forces
that exist. All other forces are some combination of these. This is physics
talking and not me.

http://en.wikipedia.org/wiki/Fundamental_interaction


From here one doesn't even have to do any estimation. If there are only 4
forces in the physical world then any macroscopic forces must be derived
from these 4. Friction is not a fundamental force. It is based on the
interactions of a huge number of atoms and the 4 forces. Mechanical
"bounce" is not due to some macroscopic force(although we can use an average
to get it) but only due to the 4 forces. I don't see how you can conclude
anything else. I am not saying that we cannot talk about some derived force
because its almost necessary. What I am saying, now atleast, is that
everything in the physical world is due to these 4 forces(assuming they are
the correct). Any force that you claim is "fundamental" better be one of
these 4 forces and if its not then you better prove it(atleast make enough
of a convincing argument so that it is accepted as a new fundamental force).

If you want to talk about friction or bounce or whatever and ignore the fact
that they exist only because of these 4 forces then you are doing yourself a
disservice. You might get along just fine with beliving that but your no
different than those who thought the world was flat or that the thunder god
was angry at them.





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