Originally Posted by oxygenhose
Now try and defend the logic that scratch resistant products are a fraud.
Okie doke, I'll give it a shot.
Let us start with two fundamental assumptions. First assumption: Anything that can scratch glass much necessarily be harder than glass. Fair enough?
Second assumption: Mere contact between glass and something harder than glass is insufficient to create a scratch. There must be some minimal amount of pressure applied, along with a force parallel to the surface of the glass. In other words, you have to push the things together and slide. Common sense, yeah?
Now. Imagine that you have a piece of the same optical glass used in iPhone screens, and also something hard enough to scratch it. Since optical glass has a Mohs hardness of six-and-a-half-ish, we're looking for something with a hardness of seven or more. Just to be on the safe side, let's go with tungsten carbide. That's ridiculously hard, with a Mohs rating of 9.
Now apply the tungsten carbide drill bit to the glass. Apply sufficient parallel and perpendicular forces to make a scratch. Write down the values of the parallel and perpendicular force components in your copybook.
Now apply one of these plasticky sheety things to the glass. Apply the drill bit again, using the same force we used before.
What happens? By gosh and by gum, the drill bit went right through the plastic like it wasn't even there. Seems like the plastic did absolutely no good whatsoever. Because, see, an object hard enough to scratch glass,
applied with sufficient force to scratch glass,
isn't going to be all that impressed by a piece of sellotape.
On the other hand, if we bring the drill bit and the plastic-wrapped glass together with sufficiently small
force that it doesn't puncture the plastic, then we're not using nearly enough force to scratch the glass. So the "protection" the plastic provided was, in fact, useless.
That's the logic in a nutshell. Any contact with a sufficiently hard object, applied with enough force to be able to scratch the glass, will destroy the plastic. And any contact that's not sufficiently forceful to destroy the plastic cannot (by virtue of the plastic being softer) scratch the glass. In between, we have a whole set of possible contact scenarios where the plastic is damaged or destroyed but the glass remains unharmed, because glass is harder than plastic.
Originally Posted by oxygenhose
Welcome to science class buddy! - the dirt, sand and dust particles in your pocket, purse... well in fact everywhere on this rock inhabited by moronic apes, is the same material as glass and 'hard' enough to scratch it. Duh.
Sorry, but that's untrue. If that were correct, then charcoal briquettes would be just as hard as diamonds, since they're both allotropes of pure carbon.
I think this is the part where I'm supposed to say "duh," but instead I'll just elaborate, 'cause I'm that kind of guy. See, chemical composition does not determine material hardness. That comes down to molecular structure. Diamond is harder than charcoal because it's got a different molecular structure. While you can
find particles that can scratch glass — quartz sand, for example — that's not the same as saying that everything everywhere can scratch glass.
You don't deal with glass very much do you? You can in fact scratch it with your fingernail, a piece of plastic, etc.
See, that's what we in the business call — and I'm sorry to jargon this up — "wrong." When you rub a softer thing against a harder thing, it's the softer thing that deforms.
Obviously you're never 'played catch' - the cork and leather is not as hard as "glass" but it will 'scratch it' pretty damn well.
You've completely lost me, I'm afraid. Are you talking about throwing a baseball through a window? You know that scratching glass and cracking or shattering it are two entirely different physical processes, yeah?
Before you move on to economics, just a suggestion, might want to take some refreshers on science.
Perhaps you're right.
Bozo, would take a lot for your keys to 'tear thru the plastic'. Alone, they'll scratch your phone glass pretty fast…
Give it a try. Take your house key and a glass from the cupboard. See if you can scratch the glass with your house key. Consider it a refresher course in science, right in your own home.
For those of you who don't want to follow along at home, I'll give the answer away. The kind of glass used to make things like window panes and drinking glasses has a hardness of around five and a half. Brass, which is the metal most keys are made of, has a hardness of around three and a half. You cannot scratch glass with brass. You can
scratch that kind of glass with a high-carbon steel knife, which has a hardness that approaches six, but it's very difficult. You're more likely to break the glass or cut yourself if you're not very careful, because of the amount of force required.
Optical glass is harder than household glass. It's very, as the phrase goes, scratch-resistant.