Just hoping to keep track of this, if anyone is able to help with it.

Would anyone be able to somehow verify whether a laptop sitting on a coffee table, if pushed on to the floor, could possibly smash the screen?

My thoughts would be that the only damage sustainable would be a potentially damaged hard drive?

Here’s the specifics. Let me know if there’s anything else needed, and I’ll give details where I can.

• The floor is carpeted
• Coffee table is 30cm tall
• Laptop weighs 2.5kg

And by “smashed laptop screen” I mean something like this:

Trying to catch someone out?

Is the lap top open?

furious said:

Trying to catch someone out?

Is the lap top open?

Sort of yes, sort of no.

Laptop open, let’s say it’s closed.

JTQ said:

furious said:

Trying to catch someone out?

Is the lap top open?

Sort of yes, sort of no.

Laptop open, let’s say it’s closed.

I’ve got s feeling this is not going to be easy.

7.4 joules need to be expended somehow,

Peak Warming Man said:

I’ve got s feeling this is not going to be easy.

I’m not familiar with the equations or anything else to do with something like this, but was hoping someone here would know how to go about it.

Basically the idea behind the question – it’s been written in “her” affidavit that our son pushed my laptop off the coffee table and it hit the floor and the screen smashed. Truth is though, she couldn’t find the document she was looking for, and slammed the screen shut, which smashed the screen. Nice of her to blame our son for it.

I’m not going to be presenting any of this in court. There’s no point in it. I’m not trying to prosecute her, I’m just trying to get access to my son. But the point of the question, is I’m just wondering how it would be figured out – whether it has the potential to smash the screen, or whether it’s proven to not be true at all.

sibeen said:

7.4 joules need to be expended somehow,

7.4 joules? This is where I’m wondering how it’s worked out. I’m assuming there’s an equation in there that gives that answer?

And then curious what the next step entails – how would you figure out what happened next. Does the 7.4 joules put the pressure on to the screen, and have that smash it? Or is 7.4 joules unlikely to have that level of effect?

Again my thoughts was that from a 30cm height, it wouldn’t be enough to smash the screen, but only potentially damage the hard drive. If that.

• Again my thoughts was that from a 30cm height, it wouldn’t be enough to smash the screen, but only potentially damage the hard drive. If that.

It would also depend how it landed…

JTQ said:

sibeen said:

7.4 joules need to be expended somehow,

7.4 joules? This is where I’m wondering how it’s worked out. I’m assuming there’s an equation in there that gives that answer?

And then curious what the next step entails – how would you figure out what happened next. Does the 7.4 joules put the pressure on to the screen, and have that smash it? Or is 7.4 joules unlikely to have that level of effect?

Again my thoughts was that from a 30cm height, it wouldn’t be enough to smash the screen, but only potentially damage the hard drive. If that.

0.3 metres * 1 g * 2.5 kG = 7.4 joules

sibeen said:

0.3 metres * 1 g * 2.5 kG = 7.4 joules

Thanks :)

Forensics experts try to replicate patterns by testing.

sibeen said:

JTQ said:

sibeen said:

7.4 joules need to be expended somehow,

7.4 joules? This is where I’m wondering how it’s worked out. I’m assuming there’s an equation in there that gives that answer?

And then curious what the next step entails – how would you figure out what happened next. Does the 7.4 joules put the pressure on to the screen, and have that smash it? Or is 7.4 joules unlikely to have that level of effect?

Again my thoughts was that from a 30cm height, it wouldn’t be enough to smash the screen, but only potentially damage the hard drive. If that.

0.3 metres * 1 g * 2.5 kG = 7.4 joules

the shockwave is probably what does cracks the screen

Arts said:

Forensics experts try to replicate patterns by testing.

Lol.. I only have 1 laptop and I’ve already replaced the screen once :)

JTQ said:

Arts said:

Forensics experts try to replicate patterns by testing.

Lol.. I only have 1 laptop and I’ve already replaced the screen once :)

I have replaced three drives in the laptop I have

one from bed height drop to the floor

the others from heat damage

I have a WD two in one SSD and Sata HD in it now

JTQ said:

Just hoping to keep track of this, if anyone is able to help with it.

Would anyone be able to somehow verify whether a laptop sitting on a coffee table, if pushed on to the floor, could possibly smash the screen?

My thoughts would be that the only damage sustainable would be a potentially damaged hard drive?

Here’s the specifics. Let me know if there’s anything else needed, and I’ll give details where I can.

• The floor is carpeted
• Coffee table is 30cm tall
• Laptop weighs 2.5kg

And by “smashed laptop screen” I mean something like this:

I have a similar crack pattern in my GPS, and don’t know how it happened, either by a fall from 1.5 metres onto a carpeted floor or from squeezing the side too hard when removing from the mount. Earlier a mobile phone cracked the same way. A fall of my laptop caused the following damage, resulting in loss of WiFi connectivity. I wasn’t around at the time of the fall, but it was probably the fall off a bed.

The cracking of glass is notoriously difficult to predict. That’s because it is brittle fracture, microcracks (and scratches) that occur at surfaces over time greatly reduce the overall strength, which can vary by a factor of 10 or more even under identical impact conditions. Also, glass thickness would vary from laptop to laptop. I have several books at home that contain information on the strength of glass under impact loading, I even did a study once at work for a solar panel manufacturer, but let me first be lazy and check the internet.

http://glassproperties.com/references/MechPropHandouts.pdf

Use the 7 MPa design strength suggested on the first slide. (Later slides suggest that 10 or 14 MPa may be more realistic). I don’t see anything on the web telling me the thickness of laptop glass, let’s temporarily call it t. For impact calculations, you’ll also was a deceleration distance d. On a carpeted floor, that’s going to be much less than a mm, let’s say d = 0.1 mm, though it could be as large as 0.2 mm.

(to be continued)

Use t = 0.7 mm.

mollwollfumble said:

Use t = 0.7 mm.

As for this, it is difficult to buy 1mm glass anywhere far from the manufacturer as it is practically difficult to ship it without unacceptable breakages.

sibeen said:

0.3 metres * 1 g * 2.5 kG = 7.4 joules

Let’s set bending modes and bearing areas aside for the moment and just concentrate on loads.

I just measured the load from a malicious sustained push for laptop on table and laptop on floor. For laptop on table I get 6 kg = 60 Newtons. For laptop on floor I get 10 kg = 100 Newtons.

For impact on carpet, deceleration over 0.1 mm I get 7.4 / 0.0001 = 74000 Newtons. Deceleration over 0.2 mm gives 7.4 / 0.0002 = 37000 Newtons.

So the load can be very much more for accidental fall on carpet than for a malicious push.

From that, I can safely say that, no matter what bending modes and bearing areas are assumed for the two cases, an accidental fall is far more likely to cause the damage observed than a malicious push. More to the point, in a court of law you could never claim that a malicious sustained push was to blame.

Now let’s look at what bearing area could give a stress of 7 MPa from 74000 Newtons. The glass thickness is 0.7 mm and side length 170 mm. The bearing area affected would be much less than that 170 mm, but then again the mode of failure would be different too, so let’s trade the two sources of error off against one another. 74000 / 0.7 / 170 = 620 MPa >> 7 MPa. So even allowing for inaccuracies in the calculation, a fall from coffee table onto carpet could quite easily crack the screen of a laptop.

Let’s also check the case of a malicious push. 100 / 0.7 / 170 = 0.84 MPa << 7 MPa. So a sustained malicious push couldn’t crack the screen of a laptop.

That’s very detailed. Thanks mollwollfumble :) Much appreciated.

Not going to be taking it to court, but was just curious about it.

Basically my ex couldn’t find the document she was looking for, so she slammed the screen shut and it smashed the screen. But she’s written in her affidavit that our son pushed the laptop off the coffee table which broke the screen, and I apparently smacked him hard for it.

JTQ said:

That’s very detailed. Thanks mollwollfumble :) Much appreciated.

Not going to be taking it to court, but was just curious about it.

Basically my ex couldn’t find the document she was looking for, so she slammed the screen shut and it smashed the screen. But she’s written in her affidavit that our son pushed the laptop off the coffee table which broke the screen, and I apparently smacked him hard for it.

Oh dear, you don’t remember?

The time I punched miss m is very raw in all our memories, despite it being more than ten years ago, it was the first time I got a tongue lashing from mrs m. I never smacked miss m.