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  1. Rhody's Avatar
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    #21  
    Quote Originally Posted by dave75 View Post
    You could have a completely frictionless surface and it would stay in place.
    You're still not technically disagreeing with the post that you stated you disagreed with.
  2. #22  
    hmmm ... this was know info, but i didn;t see anyone posting opn it before.

    Maybe this is being a bit dramatic, but I really don't like the idea of a back that does not 'macth' the rest of the phone.

    Add this on top of the fact the Touchstone might be expensive (over $50) and will require a seperate purchase of the phone back, all to do something i can do just by plugun g the phone in, and i think i'm skipping this purchase.

    (& sorry for the run on sentance)
    da Gimp

    Please note: My spelling sucks and I'm to lazy to check it.
  3. #23  
    Quote Originally Posted by dave75 View Post
    Sorry, but I have to disagree. The magnets are not only applying forces in the normal plane. They are also applying tangential forces that far exceed the tangential forces applied by the weight of the Pre. You can see this in the demos when the Pre snaps into place. I think the matte finish is to hide scuffing because the Pre will rub on the Touchstone with fairly high forces.
    Quote Originally Posted by dave75 View Post
    You could have a completely frictionless surface and it would stay in place.
    I really doubt that the original poster intended for this thread to become a physics discussion, and I apologize to all for my comments (both above and more in this post) having diverting it off topic.

    Back a little closer to the original topic, I think there are probably several reasons for the matte finish. I happen to like the finish on my 755p, which seems to be a rubberized coating. If I ever get a Pre, I would be quite pleased if it had this same finish.

    And back to the off-topic physics...as for the magnets applying a tangential force, to the best of my recollection, magnetic forces are attraction and repulsion. Yes, the attraction force could easily be great enough to hold the Pre onto a frictionless surface, perhaps even great enough to exceed the weight of the Pre and suspend it from the bottom of a horizontal surface. (Wasn't there a video with the Pre falling off the Touchstone onto the floor? Probably some inertial forces involved there.)

    The only "tangential" magnetic force I can think of occurs if the magnet and the metal it is attracting have become misaligned so that the attraction force is not normal to the surface. This would be the case if the Pre is placed upon the Touchstone in a misaligned position and the attraction force pulls them into alignment ("snaps into place" as Dave75 described). In that case, friction works against the desired movement. Or in the case of weaker magnets and low friction, the Pre might slide down the slope of the Touchstone until there is misalignment and the tangential component of the attraction force keeps it from sliding farther. More friction helps prevent the undesired motion in that case, which was the point of my original comment. Depending on how you view this, I am either agreeing or disagreeing with Dave75.

    An interesting experiment related to this second low-friction case is to place a reasonably strong magnet on a large, fairly smooth steel surface or perhaps to place a thin, low-friction material between the magnet and the steel surface. If the friction is low enough, then it is much easier to remove the magnet by sliding it over the surface to an edge than to pull it directly away. If the surface is vertical and the friction is low enough, the magnet may slide right down. This is often observed with refrigerator magnets trying to hold up a kids' artwork. Hopefully, that would never be the case with a Pre and a Touchstone.

    So everyone go ahead and bash me for being off topic, for being too wordy, or for living under different laws of physics than you have observed. I will try not to post any more of this stuff. And I don't think I need any more expressions of affection from Pooh!
    Dr J

    Palm III --> Palm m500 --> Treo 600 --> Treo 650 (2 days!) --> Treo 700p --> Treo 755p (Sprint)
    KayPro II --> IBM Portable --> Mac SE --> Mac Performa 6115CD --> Mac PPC 6500 --> Mac G4 (Yosemite) --> iMac G5 20
  4. #24  
    what?



    ;-)
    da Gimp

    Please note: My spelling sucks and I'm to lazy to check it.
  5. dave75's Avatar
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    #25  
    It's a little off topic, but my point was that the matte finish is more likely to hide scuffing as opposed to any gains in frictional forces, in my opinion. It was a fun discussion though.
  6. dave75's Avatar
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    #26  
    Quote Originally Posted by Rhody View Post
    You're still not technically disagreeing with the post that you stated you disagreed with.
    The original post said that friction helps keep the Pre in place and I said it will stay in place with no friction at all. How am I not disagreeing? It's not a big deal, I was just having some fun.
  7. Rhody's Avatar
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    #27  
    Quote Originally Posted by dave75 View Post
    The original post said that friction helps keep the Pre in place and I said it will stay in place with no friction at all. How am I not disagreeing? It's not a big deal, I was just having some fun.
    I'm having fun.

    Even if the Pre will stay in place without friction, that does nothing to dispute his assertion that friction also helps to keep it in place. So rather than actually disagreeing with him, you merely presented a different point.

    Think of it this way. Consider that there is some ice and it's 90 degrees outside, and then someone put some salt on the ice. Person A says, "salt helps to melt ice." Then, person B says, "I disagree. It's 90 degrees and the ice will melt anyway." Did person B really disagree with person A?

    Anyway, I'm bored. I think I'll go have lunch.
  8. #28  
    I don't know whether the magnets alone is enough or not, but I stick by my assertion that the main point of the soft back is to increase friction to prevent it from sliding off. Even if it would be possible with a gloss back, I bet the soft back makes it stick even better.

    Engadget agrees with me.

    "The inductive charging accessory -- which seems like an almost automatic purchase for any Pre buyer with a single geeky bone in their body -- needs magnets in the Pre to hold it in place when it's attached, but it turns out that the standard glossy battery cover doesn't have those magnets. Instead, the Touchstone will include a replacement cover that has the magnets and loses the gloss for a stickier matte soft-touch surface, ostensibly to help secure the phone against the charger's slanted top."

    On a phone that Palm says the style was a top priority, why would they change materials on the back if their wasn't a good reason? I'm thinking the soft back won't do much for the phone in the looks department.
  9. dave75's Avatar
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    #29  
    Quote Originally Posted by Captweez View Post
    I don't know whether the magnets alone is enough or not, but I stick by my assertion that the main point of the soft back is to increase friction to prevent it from sliding off. Even if it would be possible with a gloss back, I bet the soft back makes it stick even better.

    Engadget agrees with me.

    "The inductive charging accessory -- which seems like an almost automatic purchase for any Pre buyer with a single geeky bone in their body -- needs magnets in the Pre to hold it in place when it's attached, but it turns out that the standard glossy battery cover doesn't have those magnets. Instead, the Touchstone will include a replacement cover that has the magnets and loses the gloss for a stickier matte soft-touch surface, ostensibly to help secure the phone against the charger's slanted top."

    On a phone that Palm says the style was a top priority, why would they change materials on the back if their wasn't a good reason? I'm thinking the soft back won't do much for the phone in the looks department.
    I said multiple times why I thought, to hide scuffing. As the Pre snaps into place it is pulled and into the Touchstone and it will rotate slightly. Over time, a nice glossy surface will have a lot of scuff marks.

    To Rhody, how about this example. You have a Ford F150 and a kid on a tricycle pulling a boat trailer. The kid on the tricycle is exerting a force on the trailer, but does it really matter? That kid isn't why the boat trailer is moving, but I will not deny he is there. The additional friction force exists, but is very small compared to the forces of the magnet.

    OK, I think I've talked enough physics, sorry.
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