Crash and helmet

For all discussions about this "lively" subject. All topics that are substantially about helmet usage will be moved here.
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Crash and helmet

Post by Jdsk »

jois wrote: 28 Sep 2022, 10:48am
Jdsk wrote: 28 Sep 2022, 10:37am
jois wrote: 28 Sep 2022, 10:30am
Ok il take that as a concession. He didn't "measure " it now by your own admission

Can you provided an explicit link to anyone measuring it ever ?
He didn't measure radiation pressure. He did measure the momentum of the photon by a different method. The experimental details and the results are in the 1923 paper.

I suggest choosing a physics textbook and seeing what that says.
If he didn't measure it he calculated it. There is no other options. I've not disputed at any point it can be calculated
What do you mean by "it". The momentum of the photon or radiation pressure?

Thanks

Jonathan
jois
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Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Jdsk wrote: 28 Sep 2022, 10:51am
jois wrote: 28 Sep 2022, 10:48am
Jdsk wrote: 28 Sep 2022, 10:37am
He didn't measure radiation pressure. He did measure the momentum of the photon by a different method. The experimental details and the results are in the 1923 paper.

I suggest choosing a physics textbook and seeing what that says.
If he didn't measure it he calculated it. There is no other options. I've not disputed at any point it can be calculated
What do you mean by "it". The momentum of the photon or radiation pressure?

Thanks

Jonathan
I'm under the impression we are discussing momentum ?
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Crash and helmet

Post by Jdsk »

Compton measured the momentum of the photon. The experimental method and results are in the 1923 paper, and specifically in the section labelled "Experimental Test" and the subsection labelled "Wave-length (sic) of the scattered rays".

Jonathan
jois
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Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Jdsk wrote: 28 Sep 2022, 11:02am Compton measured the momentum of the photon. The experimental method and results are in the 1923 paper, and specifically in the section labelled "Experimental Test" and the subsection labelled "Wave-length (sic) of the scattered rays".

Jonathan
It's only of academic interest I'm not devoting all day to trying to get a straight answer out of you. Particularly as I know I'm correct.

You've had all the chances I'm prepared to give to post an explicit statement.
mattheus
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Location: Western Europe

Re: Crash and helmet

Post by mattheus »

What are the units of "perspective", and how does one measure it?
jois
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Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Further unmeasured only calculated physics standards includes the speed of light.

That is, it's impossible to measure it one way. It's always a return journey which then requires both a calculation and the quite important assumption it's the same speed in both directions. Which it may or may not be. No one knows
Steady rider
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Joined: 4 Jan 2009, 4:31pm

Re: Crash and helmet

Post by Steady rider »

Post by Tiggertoo » 12 Aug 2022, 9:56pm wrote
I crashed last Friday - wheels went out from under me on a tight/wet curve - and banged up my knee, arm and thigh (all mendable), but for the first time crashing - I have done it a few times (mostly by dogs) my head hit the pavement hard and set my head pounding.

The reason I am posting this thread is that my helmet broke along the side receiving the blow. If I had not been wearing the helmet, I would not be here today to write this.
The sides of helmets are the weakest part and helmets can fracture at a fraction of the forces to fracture a skull, so it is very likely he would have survived and perhaps without a helmet the impact force may have been lower or even a near miss.
It looks like helmets may crack at about 50-100kg and skulls at about 200-500kg
http://www.ta.org.br/site/Banco/7manuai ... helmet.pdf
Last edited by Steady rider on 28 Sep 2022, 12:02pm, edited 1 time in total.
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Crash and helmet

Post by Jdsk »

It's possible to measure the speed of light with a common household appliance. Everyone should do it once.

Other methods are also available:
https://en.wikipedia.org/wiki/Speed_of_ ... easurement

Jonathan
Stevek76
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Joined: 28 Jul 2015, 11:23am

Re: Crash and helmet

Post by Stevek76 »

jois wrote: 28 Sep 2022, 1:45am
They don't have mass at all according to a professor at fermilab, or specifically the mass is an illusion
I'd be careful about relying too much on slightly hyperbolic statements made on lightweight documentaries (which is basically all of them when it comes to this sort of specialism in a subject). When people start talking about things like that it's really getting into metaphysical interpretations and debate of what the maths of topics like quantum physics means and semantics about what a term like 'mass' really means.

As it is, when it comes to the actual number crunching, quantum mechanics, QFT etc are littered with mass terms as anyone who's actually studied and been examined in it would know. Much like basic mathematical operators and everything else, we agree a definition so that everyone knows what we're all talking about. Within those definitions, photos have momentum but no mass and mass is a specific property with specific affects on other things.
The contents of this post, unless otherwise stated, are opinions of the author and may actually be complete codswallop
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Crash and helmet

Post by Jdsk »

Stevek76 wrote: 28 Sep 2022, 12:23pm ...
As it is, when it comes to the actual number crunching, quantum mechanics, QFT etc are littered with mass terms as anyone who's actually studied and been examined in it would know. Much like basic mathematical operators and everything else, we agree a definition so that everyone knows what we're all talking about. Within those definitions, photos have momentum but no mass and mass is a specific property with specific affects on other things.
Yes.

And, following the discussion upthread, protons and neutrons have rest mass and photons don't, or any other sort of mass.

Jonathan
Stevek76
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Joined: 28 Jul 2015, 11:23am

Re: Crash and helmet

Post by Stevek76 »

Steady rider wrote: 27 Sep 2022, 5:11pm It looks like helmets may crack at about 50-100kg and skulls at about 200-500kg.
All this probably shows is that helmets will crack at lower impact forces than that required to crack an adult skull. Other people may find more accurate results.
I don't doubt that helmets have lower structural integrity than skulls however for an impact they don't need to have higher integrity to still spread the impulse across a wider patch of the skull which in turn may bring any localised stresses under the thresholds needed to cause a fracture.
mattheus wrote: 27 Sep 2022, 11:21am
Stevek76 wrote: 26 Sep 2022, 12:01pm I think people can be OTT when misquoting others just to make themselves seem cleverer.
Yes, I think they can Steve. Well done on joining that bandwagon!
Not sure I was misquoting there? I hadn't really clocked the bracketed part I'll admit but I don't think I went through excessive mental gymnastics to get to 'insignificant' given you'd listed fracture in with 'the rest' after noting that rattling does all the significant damage, hence my apparent misunderstanding.
Anyway ..... my initial point was that creating some sound energy doesn't help you much if your brain is still going to get a shove around your skull. It's that brain rattling that does all the significant damage - the rest is just cuts, bruises, and sometimes a skull fracture.
(The latter isn't fun, but not a disaster - you will see professional footballers with those natty mask things holding theirs together on the pitch, and pro cyclists often compete with pinned shoulders, splinted fingers etc etc.)
The contents of this post, unless otherwise stated, are opinions of the author and may actually be complete codswallop
mattheus
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Location: Western Europe

Re: Crash and helmet

Post by mattheus »

Steve, you do realise that "significant" is a purely relative word, right? Context is rather important.

Yes, I'm happy to state that: concussions and other brain damage are more significant than a simple, complication-free fracture.

Feel free to propose other phrases to put in my mouth, and I'm happy to give my views on them. Fair?

(Whilst also noting that I was once on the "probably dying" list for several days due to complications from a tibia fracture - an injury generally considered far from life-threatening, not leading to cries for PPE - yes, the body CAN be complicated, with unforeseen interactions, who knew??)

AN ASIDE: It's also interesting to note that given the manufacuturers have told us helmets do not reduce concussions, helmet evangelists must rate skull fractures, cuts AND bruises as more significant than concussion. Assuming they've done their research, which I'm sure they have.
jois
Posts: 334
Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Jdsk wrote: 28 Sep 2022, 12:27pm
Stevek76 wrote: 28 Sep 2022, 12:23pm ...
As it is, when it comes to the actual number crunching, quantum mechanics, QFT etc are littered with mass terms as anyone who's actually studied and been examined in it would know. Much like basic mathematical operators and everything else, we agree a definition so that everyone knows what we're all talking about. Within those definitions, photos have momentum but no mass and mass is a specific property with specific affects on other things.
Yes.

And, following the discussion upthread, protons and neutrons have rest mass and photons don't, or any other sort of mass.

Jonathan
We have done that, how does a thing who's constituent parts have no mass develop mass ?
jois
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Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Jdsk wrote: 28 Sep 2022, 11:56am It's possible to measure the speed of light with a common household appliance. Everyone should do it once.

Other methods are also available:
https://en.wikipedia.org/wiki/Speed_of_ ... easurement

Jonathan
T hey did it first with a mechanical driven gear wheel which is quite clever if not greatly arcuate, but only two ways. Nobody know what it's one way speed is
jois
Posts: 334
Joined: 22 Sep 2022, 12:29pm

Re: Crash and helmet

Post by jois »

Stevek76 wrote: 28 Sep 2022, 12:23pm
jois wrote: 28 Sep 2022, 1:45am
They don't have mass at all according to a professor at fermilab, or specifically the mass is an illusion
I'd be careful about relying too much on slightly hyperbolic statements made on lightweight documentaries (which is basically all of them when it comes to this sort of specialism in a subject). When people start talking about things like that it's really getting into metaphysical interpretations and debate of what the maths of topics like quantum physics means and semantics about what a term like 'mass' really means.

As it is, when it comes to the actual number crunching, quantum mechanics, QFT etc are littered with mass terms as anyone who's actually studied and been examined in it would know. Much like basic mathematical operators and everything else, we agree a definition so that everyone knows what we're all talking about. Within those definitions, photos have momentum but no mass and mass is a specific property with specific affects on other things.
I'm generally favouring someone who job is devising clever ways to use partical accelerators over you on the general topic of particles
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