What do you mean by "it". The momentum of the photon or radiation pressure?jois wrote: ↑28 Sep 2022, 10:48amIf he didn't measure it he calculated it. There is no other options. I've not disputed at any point it can be calculated
Thanks
Jonathan
What do you mean by "it". The momentum of the photon or radiation pressure?jois wrote: ↑28 Sep 2022, 10:48amIf he didn't measure it he calculated it. There is no other options. I've not disputed at any point it can be calculated
I'm under the impression we are discussing momentum ?
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.
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.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.
http://www.ta.org.br/site/Banco/7manuai ... helmet.pdfIt looks like helmets may crack at about 50-100kg and skulls at about 200-500kg
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.
Yes.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.
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.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.
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.)
We have done that, how does a thing who's constituent parts have no mass develop mass ?Jdsk wrote: ↑28 Sep 2022, 12:27pmYes.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.
And, following the discussion upthread, protons and neutrons have rest mass and photons don't, or any other sort of mass.
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 isJdsk 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
I'm generally favouring someone who job is devising clever ways to use partical accelerators over you on the general topic of particlesStevek76 wrote: ↑28 Sep 2022, 12:23pmI'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.