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Anyone who has removed a sticker, knows that often they must be pulled off slowly, otherwise they tear. Why is this?

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    $\begingroup$ @Spider_Holland MythBusted :^) $\endgroup$ – Keith McClary Aug 26 at 4:47
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    $\begingroup$ @Spider_Holland No modern glass panes are "thicker at the bottom", and no car windscreen will flow. The observations on church windows were made after centuries, which lead to this theory. It has ben scientifically disproven countless times. (for reference, see this article at one of the biggest glass companies, citing various physics experts: cmog.org/article/does-glass-flow ) $\endgroup$ – WooShell Aug 26 at 7:12
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    $\begingroup$ @Spider_Holland I believe what I studied. You should believe in the correct explanation when you see it instead. $\endgroup$ – Ian Aug 26 at 11:50
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    $\begingroup$ @Spider_Holland Glass is an amorphous solid. The likely reason that some people claim that glass is an extremely viscous liquid is that it exhibits glass transition rather than phase transition. This means that it is not possible to point to a specific temperature at which glass transforms between solid and liquid; the viscosity just keeps increasing with lower temperature. $\endgroup$ – jkej Aug 26 at 12:03
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    $\begingroup$ @Spider_Holland It's a common misconception that often even gets taught to students in science classes. You can find quite a bit of information about it. For example, glass panes being thicker at the bottom for old buildings is really just a relic of how glass used to be made. It wasn't perfectly flat; and it makes more sense to install the thicker part at the bottom instead of the top. People are usually pretty quick to jump on things like that, because they don't want the misconception to keep spreading. $\endgroup$ – JMac Aug 26 at 13:14
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The glue that holds them on flows like a very viscous liquid on long time scales but is stiff on short time scales. If you pull on it suddenly, it acts stiff and holds fast, causing the paper sticker to tear. If you pull slowly, the glue flows and pulls apart before the paper has a chance to tear. This sort of behavior is called viscoelasticity.

Where does this property come from? In a goopy glue of the sort used on paper stickers and the like, the glue is actually a very viscous liquid which readily wets things like paper, plastics, wood, glass, and so forth. If you grab a blob of this stuff and pull it slowly apart, its molecular chains drag and slip past each other and the blob will slowly elongate as the chains slip. However, if you apply a large tensile load suddenly, there's no opportunity for the chains to begin slipping and the glue behaves instead like a chunk of stiff plastic.

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    $\begingroup$ Hey, is there no relation between this question and the impulse concept F∆t=∆p? $\endgroup$ – user233565 Aug 26 at 3:13
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    $\begingroup$ @Spider_Holland, I do not think so. $\endgroup$ – niels nielsen Aug 26 at 5:46
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    $\begingroup$ Most mechanical properties are strain-rate dependent, for various reasons. $\endgroup$ – Jon Custer Aug 26 at 13:45
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    $\begingroup$ that's true, even for metals. $\endgroup$ – niels nielsen Aug 26 at 17:22
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    $\begingroup$ This answer is good but it would be great to have a bit more of a discussion of why this happens. As it stands, the answer is not much more informative than the question IMO. $\endgroup$ – Javier Aug 26 at 19:36
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Along with niels awesome answer I would also like to add that when a sticker is pulled suddenly and because the sticker is not isotropic, there are parts of sticker which experience the change in stress and strain more than some other parts. Applying large force in short amount of time might cause them to tear a bit , which becomes a weak spot for it and on further application of any force it further starts tear from that edge, which ultimately causes it to tear apart completely

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To add to RandomAspirant's and niel's answers, when you pull an item quickly, you are creating not just an acceleration (which provides the force), but what is termed a 'jerk' by Halliday, Resnick, and Krane. The deriviative of acceleration is a jerk :).

Anyway, this jerk - 'j' completely changes the forces on the object. Here F_net= m* Integral(j) + "sticky forces". The first term adds the jerk which contains a time component and likely in this case a spacial component to it. This rapid pull on the sticker then creates a large jerk, creating an even larger force during that small instant when its pulled.

A slow peel however doesn't add this jerk - or at least a very very small one. F=ma due to the stick effect only which is very different.

Also, when a sticker is pulled slowly, when you watch it closely, you will see small filament strands pull up and disconnect one by one. This effectively minimizes the force due to stickiness because only a few of the bonds are being pulled apart by your hand at a given instance.

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To put it another way, there's a maximum stress that the sticker can support before it starts to permanently deform or tear. This is known as the elastic limit. If you exceed that value, it will creep and eventually fracture (or fracture instantly if you pull hard enough), however, it can withstand a lower stress without breaking.

The glue on the other hand has a very low elastic limit, and a large range of viscoplastisity, in which a small piece of it gets gradually thinner until it breaks.

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