Knocked off my bike in a cycle lane

[Moderators]

Exactly how close do you suppose the moderator's finger is to the lock button right now?

Hmmm let me see.... Touching it. .....!

Thread locked whilst I review it and decide if it has run its course.

Please try to remember the Rules and Guidelines, maybe reacquaint yourselves with the ones about being respectful to other members in the meantime!

 

[Moderators]

Thread reopened and it can be just as easily closed again if it slides back into personal abuse.

Yes there are differing opinions on this topic but you will never open someone's eyes to your point of view by merely being rude to them.

 

[doog]

[QUOTE 3729197, member: 10119"]To start with, because I've read some stuff about it and the arguments for mandatory helmet usage having a negative impact on health at a societal level seem to have some weight to them. Also the risk compensation stuff, which I've never been arsed to go read up on properly, seems like complete common sense to me which is at least as convincing as anyone's "helmets are better for safety - it's just common sense!" arguments [/QUOTE]

'This negative impact on health at a societal level.'....wheres the weight in that if you dont mind me asking?

The reason I ask is that apparently 93% of the dutch population cycle at least once a week....far more than than the UK. Yet the Dutch have exactly the same life expectancy as us.

 

[User10119]

'This negative impact on health at a social level.'....wheres the weight in that if you dont mind me asking?

The reason I ask is that apparently 93% of the dutch population cycle at least once a week....far more than than the UK. Yet the Dutch have exactly the same life expectancy as us.

It was a response to a specific question, no longer there, which didn't warrant the faff of going and rooting out a load of references re the societal implications of mandatory helmet laws from the 79bazillion threads discussing the matter that I've read, here and elsewhere, over the years.

 

[doog]

Health at a societal level is not measured solely in terms of life expectancy.

Of course, Im sure life expectancy has been conveniently ignored on this occasion. I mean long term health wouldnt have any relationship to life expectancy unless the figures added up..... correct.

 

[doog]

Thanks, so the assumption is basically worthless (due to many factors) but worth using in an anti compulsion debate.

 

[david k]

life expectancy has been conveniently ignored on this occasion.

Depends whether it suits your argument or not, I'm sure it will be dragged up when it supports their own opinion, and rubbished when it doesn't

 

[benb]

I suggest people look at the differing obesity rates between the UK and the Netherlands.

 

[Profpointy]

I suggest people look at the differing obesity rates between the UK and the Netherlands.

yes, and look how much taller the cloggies are too!

 

[benb]

yes, and look how much taller the cloggies are too!

And Dutch women are nearly all beautiful.
I think I've fallen in love with every Dutch woman I've met.

 

[PhilDawson8270]

So in order for a helmet to break, it must deform, that act of deforming is the same as the foam compressing - that absorbtion of the kentic energy of the missile (the head) will reduce the G the brain is subject to.

Helmets work by increasing the duration of a collision, for the same impulse. That is they compress to increase the length of time that the collision takes place for, this is the primary function, and is how airbags and crumple zones work.

Secondary (more often in higher priced helmets), there are design mechanisms to spread the loads through the shell, reducing force in a single area.

A single split in the polystyrene and the shell would indicate a failure, it needs careful examination to see if there was any compression. The nature of that split suggests not much force was being dissipated by design, and was quite concentrated. So, if there's no compression of the polystyrene, then it has failed, and not done anything to protect the wearer from anything other than maybe a laceration.

That's not to say helmets are useless, just that there are limitations as to their effectiveness. For what it's worth, I wear a helmet, as I believe the potential benefits outweigh the potential dangers of wearing one.

But, that does not change the science and engineering of helmets.

 

[Profpointy]

Helmets work by increasing the impulse of a collision. That is they compress to increase the length of time that the collision takes place for, this is the primary function, and is how airbags and crumple zones work.

Secondary (more often in higher priced helmets), there are design mechanisms to spread the loads through the shell, reducing force in a single area.

A single split in the polystyrene and the shell would indicate a failure, it needs careful examination to see if there was any compression. The nature of that split suggests not much force was being dissipated by design, and was quite concentrated. So, if there's no compression of the polystyrene, then it has failed, and not done anything to protect the wearer from anything other than maybe a laceration.

That's not to say helmets are useless, just that there are limitations as to their effectiveness. For what it's worth, I wear a helmet, as I believe the potential benefits outweigh the potential dangers of wearing one.

But, that does not change the science and engineering of helmets.

Don't think you mean "increasing the impulse" - maybe "decreasing" or maybe "impulse" is the wrong word. Impulse means change-of-momentum

 

[PhilDawson8270]

Don't think you mean "increasing the impulse" - maybe "decreasing" or maybe "impulse" is the wrong word. Impulse means change-of-momentum

My wording may have been slightly confusing

Impulse is a change of momentum over time
impulse =Integral(F dt) = (mv)2 − (mv)1

I meant to say increase the duration of the collision to reduce the force for the same impulse.

I have made my previous post more clear.

 

[Profpointy]

My wording may have been slightly confusing

Impulse is a change of momentum over time
impulse =Integral(F dt) = (mv)2 − (mv)1

I meant to say increase the duration of the collision to reduce the force for the same impulse.

I have made my previous post more clear.

Sorry, I know I'm being picky now - Impulse is "change of momentum" (full stop).
Change of momentum over time = force = rate of change of momentum. Equals in the sense these are definitions rather than a way of calculating one from the other.
The integration of force over time is indeed impulse- your formulae and the rest are right though.

 

[PhilDawson8270]

Sorry, I know I'm being picky now - Impulse is "change of momentum" (full stop).

Impulse requires time, there's no calculation of impulse that ignores time.

It is often calculated with a duration of 0, but it is still calculated with time.

Can you please elaborate why it is not a change of momentum of a period of time?