Re: fedora and notebooks? [OT]


John Summerfield wrote:
: Dean S. Messing wrote:
:
: > I took think the pad is a wee bit sensitive to the touch when I'm
: > banging away at the keyboard. Sometimes my thumb will brush it and
: > (at least w/in emacs) the "point" will just to where the cursor sits
: > and I'm now entering text in the wrong place. Thank goodness for the
: > powerful "undo" features of emacs. Solution: thumbs up!
:
: Touchpads are misnamed; they don't require touch. There's some kind of
: proximity detector involved.

I believe it is a capacitive sensor and depends on the Dielectric
Constant of the material between the pad and one's finger. I just did
several little experiments to check. (I'm a scientist, after all :-)

First, I took my finger and put it really close to the pad w/o
touching it. No cursor motion. (Air has a small dielectric constant.)
Then I took a thin piece of paper and tried to move the cursor by
sliding finger over paper. No go unless I pressed very hard. Paper
is pretty incompressible so I don't think it was that my finger was
getting closer. Rather the surface area of the contact was increasing
so the capacitive effect was greater the harder I pressed.

Interestingly, through a much thicker envelope glue label, my finger
had no trouble moving the cursor at normal pressure. My guess is that
the glue in between the label and the backing has a high
Dielec. Const.

Finally, I used my finger nail. Being an insulator, it had no effect
even pressing hard.

As an aside to this aside, I once worked for a company that took
security very seriously. They had RFID-activated doors installed all
over their laboratory to keep the secrets in and the intruders out.

Problem was that each door had (on the inside) a capacitive "rail"
that one could push against to open the door normally from the inside.
These were double doors with a small space between them. I wondered
one day if a wire coat hanger, bent like a hook, with me touching one
bare end from the insecure side and the other bare end through the
space touching the railing would release the lock. Voila! So much
for the $50K or so they spent on internal building security.

Ain't physics fun?

<snip>

Dean

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