I guess I just want to be able to definitively see a positive result. Like, video drop tests don't prove anything. I want an energy dissipation equation that describes the effect of using one of these.
That all being said, scratches are a totally valid reason to use a screen protector, and are the main reason I've put them on all my devices for years. JerryRigEverything always does a pick scratch test on new phones he reviews/destroys to show the actual hardness of a screen, and even GG4 screens come in at like a 5-6, meaning that every-day dirt can probably scratch them.
As for drop or impact protection though, be skeptical. I can't find any proof, science, or engineering explanation for it. Only drop test videos (lots of variables that are uncontrolled) and marketing material (obviously compromised).
I didn't really think about this when I got my smartphone. Ordering a case and a couple of $3 screen protectors was a no-brainer.
Just having anything rigid on top of the screen brings me peace of mind, so I don't actually need proof, but for the sake of argument, let's say that I did:
The simple fact that the glass (either the screen or the screen protector) breaks upon impact indicates that force (kinetic energy) got transferred and "invested" into breaking the glass. If I have a screen protector, it will absorb the energy and break before the screen does.
I'm not expecting a screen protector to save my phone from a 2m drop, but for everyday wear and tear and less extreme "accidents" it's more than enough.
What do you mean by "absorb the energy"? Energy can't just be absorbed. It still has to be transmitted to the screen somehow. The question is whether or not a screen protector changed the way the energy is transferred.
As for peace of mind, I understand. Peace of mind for scratches is why I use protectors. Not for drops though.
The energy was "invested" into physically breaking the molecular bonds. Breaking the screen protector.
The simple fact that the screen protector fractures when, for example, you drop a ball bearing on it from a certain critical height - means that the force with which the ball bearing continues (thanks a lot, momentum) through to whatever is beneath that glass is reduced by the force required to fracture the screen protector... in as layman's terms as I am capable of putting it.
I understand what you're trying to say, but that's not how energy transfer really works. Look at these tests on YT that involve hammer strikes.
Try to think of this scenario. You turn your hand palm-up in a claw-like grip. You take a hammer and your drop it onto your hand from a height of 5 feet. This will hurt your hand, assuming a dead-center palm strike. Now you hold a glass screen protector in your fingers, suspended over your palm. Your drop the hammer again. 1 of two things will happen (assuming you hold on tight!). Either the hammer will blast through the glass and (neglecting fragment injuries) will still strike your hand at a high speed, injuring you, or the glass will fail to break and your fingers will get injured by the impact. If the glass sheet was perfectly hard, scenario 2 would happen. If the glass sheet breaks, then scenario 1 happens. In a world with partially elastic materials, a combination of both happens, but a vast majority of the kinetic energy from the drop is still transmitted into your hand.
I submit that the glass has a negligible strength when compared to Gorilla Glass. The energy required to break these thin sheets of tempered protective glass is negligible when compared to the energy contained in a drop/impact. It's benefit is in that a surface chip (which weakens the glass) occurs on this superficial layer instead of the device screen itself. This is an important feature, as the kiss-of-death for glass is a chip or that first tendril of a fracture. However, a film or plastic screen protector can provide this same service of simply being a boundary to discourage small chips.
@KingArthur who said anything about dropping hammers on phones from 5 ft?
On a side note:
I agree, my fingers will be injured. Doesn't exactly apply to real world scenarios. What does having five small points of contact on the glass have to do with the case of screen protectors which are meant to be in complete contact with the surface they are supposed to protect? It's all about distributing the impact over a larger surface.
When you say "vast majority" you are talking about percents. Whether it is a vast majority and exactly how much percent depends on the applied force. Because the force required to fracture the glass is constant. In fact this would be a good test methodology.
The force required to shatter/fracture the protective glass is a constant and depends on the glass itself, all other factors being equal: so let's say we use the same ball bearing every time, and lay the protective glass on the same exact surface every time (a phone or another piece of protective glass).
This means that if we were to drop a ball bearing on the glass from 2 cm, the glass will not break, but as we increase the height from which the bearing is dropped we should reach a "critical height" where the glass starts to fracture after a drop. I claim that even if the phone glass is much tougher than the protective glass, having the screen protector increases the "critical" height from which the bearing can be dropped on the phone without fracturing the phone screen, but definitely fracturing the screen protector.
Personally, I'm a fan of tempered glass screen protectors. I never liked the feel of the plastic ones, but the higher-hardness tempered glass ones have faired well for me and and managed to feel like it wasn't there.
I personally think its up to the owner of the device. All my phones have had screen protectors built into the cases. Supcase is the brand I buy for a fairly inexpensive price. When I take it off for cleaning I notice microscratches which are far from ideal.
There is such a thing as hardness. Sure it's getting harder and harder to scratch but anything that is harder than the screen for example sand, will scratch the screen.
Exploding fragments is a form of kinetic transfer. By scientific logic, whatever energy was dissipated in that action could be enough to prevent the glass behind it from shattering
