Are helmets now compulsory?

always_tyred

dondare wrote:

Molecular bonds are neither compressed nor expanded when force is transmitted through an object. (Unless you are classing the weak interactions between molecules as bonds, rather than the stronger forces that hold the molecule together.)

But you could introduce conformational strain, which would be released with a "boing" noise.

itsbruce

dondare wrote:

Breaking and/or exciting bonds requires energy. Heat will not be released.

I never said it would; quite the reverse, because I was discussing dissipation at that point.

This has meandered far from the original point of contention, which was the claim that a helmet which fractures has still provided all the mitigation that an unfractured helmet would; that in both cases X amount of damage/acceleration/force was subtracted. It's simply not a valid assumption. It is a simplistic one.

rjsterry

The other thing to consider is that in a real accident (which is after all what we are really interested in), it is quite possible that the head could sustain more than one impact, so simply looking at the helmet afterwards without any other information is unlikely to allow you to be able to determine whether it 'worked' or failed in any meaningful way.

dondare

itsbruce wrote:

dondare wrote:

Breaking and/or exciting bonds requires energy. Heat will not be released.

I never said it would; quite the reverse, because I was discussing dissipation at that point.

This has meandered far from the original point of contention, which was the claim that a helmet which fractures has still provided all the mitigation that an unfractured helmet would; that in both cases X amount of damage/acceleration/force was subtracted. It's simply not a valid assumption. It is a simplistic one.

The original point is that the Beeb reported that London cyclists would be fined ifor not wearing a helmet, and that this was incorrect. This thread started meandering after about the third post.
Whether and how helmets actually work is neither here nor there. It's too hot to wear one today, anyway. -

dondare

rjsterry wrote:

The other thing to consider is that in a real accident (which is after all what we are really interested in), it is quite possible that the head could sustain more than one impact, so simply looking at the helmet afterwards without any other information is unlikely to allow you to be able to determine whether it 'worked' or failed in any meaningful way.

Another thing to consider is that a real accident could occur when you are not cycling and therefore not wearing a helmet in any case.

MonkeyMonster

rjsterry

Anyway, could I direct the chemists more usefully to the rain thread so that they can answer the question of whether surfactants in the Gulf of Mexico could make their way to the UK via precipitation?

dondare

rjsterry wrote:

Anyway, could I direct the chemists more usefully to the rain thread so that they can answer the question of whether surfactants in the Gulf of Mexico could make their way to the UK via precipitation?

Yes.

always_tyred

itsbruce wrote:

dondare wrote:

Breaking and/or exciting bonds requires energy. Heat will not be released.

I never said it would; quite the reverse, because I was discussing dissipation at that point.

This has meandered far from the original point of contention, which was the claim that a helmet which fractures has still provided all the mitigation that an unfractured helmet would; that in both cases X amount of damage/acceleration/force was subtracted. It's simply not a valid assumption. It is a simplistic one.

Does your computer have a virus that garbles the keyboard input or something?

You were discussing dissipation, but you did say that breaking bonds released (by which we assume you mean dissipated) energy.

As to your second point - its hard to argue with someone who doesn't understand the question. The original point I made was that a fractured helmet may, or may not, have deformed in the intended manner, before fracturing. This in response to your contention that a fractured helmet necessarily indicated that the helmet had not functioned (and you went on to say that it would actually make thinkgs worse by focussing force, and not functioning as intended to cause energy too be released into your skull, but lets move on from that one shall we?)

So whereas you contend that a fracture must indicate that the helmet failed to function, I merely pointed out that it MAY indicate that a helmet failed to function.

Do you sell T-shirts for a living, by the way?

rjsterry

dondare wrote:

rjsterry wrote:

Anyway, could I direct the chemists more usefully to the rain thread so that they can answer the question of whether surfactants in the Gulf of Mexico could make their way to the UK via precipitation?

Yes.

Ta.

dondare

rjsterry wrote:

dondare wrote:

rjsterry wrote:

Anyway, could I direct the chemists more usefully to the rain thread so that they can answer the question of whether surfactants in the Gulf of Mexico could make their way to the UK via precipitation?

Yes.

Ta.

But (probably) not enough to bother us much. I would suspect that the lighter fractions of the petroleum would be a bigger problem.
But still not a very big problem.