On Sat, 20 May 2023 09:27:10 -0000 (UTC), Tweed
<usenet.tweed@gmail.com> wrote:

>The cracks are showing all over the BBC. It’s what you get when funding is
>reduced by inflation over multiple years.

I think it's now becoming clearer than ever before what happens when
funding is fixed and not dependent on any aspect of the product.

Rod.

In article <calj6itb697d5nmkg4ba0046s0u72cmrto@4ax.com>, Roderick Stewart
<rjfs@escapetime.myzen.co.uk> wrote:
> On Sat, 20 May 2023 09:27:10 -0000 (UTC), Tweed <usenet.tweed@gmail.com>
> wrote:

> >The cracks are showing all over the BBC. It<s what you get when funding
> >is reduced by inflation over multiple years.

> I think it's now becoming clearer than ever before what happens when
> funding is fixed and not dependent on any aspect of the product.

Also shows up as a rise in repeats-of-repeats to fill in for lack of new
material. The website also shows up the rise in 'symulcasts'where the same
item is on radio, but also videoed and available as such. As I write this
BBC R Scotland has its 'Sunday Show' on TV + Radio for the first part, then
continues on radio after the 'TV part' ends.

Phil Space is getting more time on air. 8-]

Jim

--
Please use the address on the audiomisc page if you wish to email me.
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On 18/05/2023 16:37, Java Jive wrote:
> On 18/05/2023 12:55, #Paul wrote:
>>
>> Java Jive <java@evij.com.invalid> wrote:
>>>
>>> The error is that the law of conservation of momentum only applies with
>>> 'perfectly' elastic collisions, ...
>>
>> Assuming translational invariance, conservation of momentum always
>> applies (although sometimes momentum can hide in odd places).
>
> Yes, my mistake, it's kinetic energy that is not conserved  -  Applied
> Maths & Physics A-Levels were a very long time ago.
>
> However, I think my description of what was happening in the video clips
> is still correct, and I note that, so far at least, you haven't
> questioned that.
>
You said "Because conservation of momentum does not apply"

I disagree with that statement. Conservation of momentum always applies.

Conservation of kinetic energy does not - because some of it may be
converted into other forms, such as heat.

In the wet sand case after the collision we have effectively a single mass.

In the loose gravel case we have
* A large mass of the bucket and the ball
* A smaller mass of the "splashed" gravel which is moving upwards.

The splashed gravel has "negative" (upwards) momentum; which means the
ball-and-bucket will have more "positive" (downwards) momentum.

Andy

On 23/05/2023 11:18, Vir Campestris wrote:
> On 18/05/2023 16:37, Java Jive wrote:
>> On 18/05/2023 12:55, #Paul wrote:
>>>
>>> Java Jive <java@evij.com.invalid> wrote:
>>>>
>>>> The error is that the law of conservation of momentum only applies with
>>>> 'perfectly' elastic collisions, ...
>>>
>>> Assuming translational invariance, conservation of momentum always
>>> applies (although sometimes momentum can hide in odd places).
>>
>> Yes, my mistake, it's kinetic energy that is not conserved  -  Applied
>> Maths & Physics A-Levels were a very long time ago.
>>
>> However, I think my description of what was happening in the video
>> clips is still correct, and I note that, so far at least, you haven't
>> questioned that.
>>
> You said "Because conservation of momentum does not apply"
>
> I disagree with that statement. Conservation of momentum always applies.

Which I have admitted was an error, but in the quote above you have
conveniently omitted the fact that I then continued ...

"to understand what's really going on, you have to understand what's
happening to the kinetic energy of the impact. In both cases, while
some of it is transmitted through the medium into downwards momentum of
its container, a significant proportion of it is also lost as heat,
sound, and distortion of the medium surface, but the crucial point is
that, because the two mediums have different elasticities, different
amounts of it is being so transmitted and lost in the two cases."

.... and all that is true.

> In the wet sand case after the collision we have effectively a single mass.
>
> In the loose gravel case we have
> * A large mass of the bucket and the ball
> * A smaller mass of the "splashed" gravel which is moving upwards.
>
> The splashed gravel has "negative" (upwards) momentum; which means the
> ball-and-bucket will have more "positive" (downwards) momentum.

As already explained, both differences in behaviour - the greater
downward movement and the greater upward movement - are both *EFFECTS*
of the differing properties of the two mediums, so neither can be the
cause, and therefore also not the explanation, of the other. So far,
I've mentioned elasticity, but actually there are at least two more
properties of the mediums which are as or more important:

* The differing densities of the two mediums. Watching the clips,
although it's difficult to be sure, I think what was going on was that
two identical containers were filled nearly to the brim with the two
mediums, so the volume of material was constant for the two experiments,
but their differing densities would then mean that in the first
experiment the momentum imparted by the ball is being applied to a
larger mass than in the second, so you'd expect a smaller displacement
of the target for the first and a larger for the second, regardless of
any other considerations.

* The wet sand is held together by surface tension of the water between
the grains, and therefore is more self-cohesive, and therefore more
difficult to distort the surface of, and hence more kinetic energy is
lost in doing so, whereas the pseudo-regolith is less self-cohesive,
much more easily distorted, and therefore less kinetic energy is lost in
doing so.

So the situation is much more complex than implied in the clip, and
regardless of whichever of these three properties is predominant in
effect, the term 'momentum enhancement' seems to me to be quite wrong
for describing what is going on.

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

In article <u4ibsm$2i7c9$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:

> So the situation is much more complex than implied in the clip, and
> regardless of whichever of these three properties is predominant in
> effect, the term 'momentum enhancement' seems to me to be quite wrong
> for describing what is going on.

Question becomes, what term would be better?

All an interesting aside as it set me wondering about the effect of having
snooker balls that aren't so hard and rigid. 8-]

Jim

--
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On 24/05/2023 11:45, Jim Lesurf wrote:
>
> In article <u4ibsm$2i7c9$1@dont-email.me>, Java Jive
> <java@evij.com.invalid> wrote:
>>
>> So the situation is much more complex than implied in the clip, and
>> regardless of whichever of these three properties is predominant in
>> effect, the term 'momentum enhancement' seems to me to be quite wrong
>> for describing what is going on.
>
> Question becomes, what term would be better?

The problem with the term is can perhaps be posed as:
How can you 'enhance' something that is preserved?

What they're trying to do is to ensure that the target object is given
the maximum possible change in velocity from the impact, so perhaps any
of 'velocity maximisation' or 'momentum transfer efficiency' or 'impact
efficiency' would be better - I think my choice would be the last.
But I'm not sure that such a term is needed anyway, because in actual
practice the properties of the target would be an unalterable given,
although some very limited amount of control might be available through
choosing the point on the surface of it to hit - which I guess was the
point they were trying to make - but it would have to be somewhere
pretty much on the line of centres, because otherwise you'd waste much
of the kinetic energy of the impact merely in setting the target spinning!

> All an interesting aside as it set me wondering about the effect of having
> snooker balls that aren't so hard and rigid. 8-]

The relevant term there is 'coefficient of restitution':

https://en.wikipedia.org/wiki/Coefficient_of_restitution

For Applied Maths A-Level, we slogged through many questions on elastic
and inelastic impacts. Playing Bar Billiards in the pub next door, as
we were lining up shots, we used to joke "If the co-efficient of
restitution is 0.9, and the angle of impact is 45 degrees ..." but of
course no-one ever played a better ball from actually trying to
calculate anything like that, it was all a matter of skill derived from
experience. As far as I knew, for much of my time at the college until
I left, I held the record Bar Billiards break, which of course I've now
forgotten the actual amount of, such is how the vanity 'achievements' of
youth subsequently get rendered irrelevant by more important events in life!

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

In article <u4l138$2vg03$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:
> > Question becomes, what term would be better?

> The problem with the term is can perhaps be posed as: How can you
> 'enhance' something that is preserved?

> What they're trying to do is to ensure that the target object is given
> the maximum possible change in velocity from the impact, so perhaps any
> of 'velocity maximisation' or 'momentum transfer efficiency' or 'impact
> efficiency' would be better - I think my choice would be the last.
> But I'm not sure that such a term is needed anyway, because in actual
> practice the properties of the target would be an unalterable given,
> although some very limited amount of control might be available through
> choosing the point on the surface of it to hit

I'd tend to go for either velocity 'maximisation' but 'enhanced' seems a
reasonable choice if defined clearly. May be clearer if velocity was used
here rather than momentum in the term as it indicates what was of interest.

> > All an interesting aside as it set me wondering about the effect of
> > having snooker balls that aren't so hard and rigid. 8-]

> The relevant term there is 'coefficient of restitution':

> https://en.wikipedia.org/wiki/Coefficient_of_restitution

But does that cover one of the 'balls' being able to break up in a way that
alters how much the 'target' velocity alters, making the dv larger?

> For Applied Maths A-Level, we slogged through many questions on elastic
> and inelastic impacts. Playing Bar Billiards in the pub next door, as
> we were lining up shots, we used to joke "If the co-efficient of
> restitution is 0.9, and the angle of impact is 45 degrees ...

FWIW we used to put coffee cups into the pocket-holes of metered tables so
we could ignore the time limit. 8-] Alas, no knowledge of basic Newtonian
mech allowed me to have any skill at snooker, etc.

Jim

--
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On 18/05/2023 21:22, Java Jive wrote:
>
> On 12/05/2023 21:08, Java Jive wrote:
>>
>> Complaint lodged as follows ...
>>
>> BBC Inside Science Degenerating Into A Talk-Show
>>
>> The last two episodes of BBC Inside Science in particular, and other
>> recent episodes more generally, have been talk-shows with little or no
>> real scientific content.  While there may be a place for such
>> talk-shows, that place is not in a science reporting programme such as
>> 'BBC Inside Science'.  Please stick to the factual reporting of
>> science, or at least remove the increasingly misleading word 'Science'
>> from the programme title.
>>
>> Discuss ... or not, as the mood takes you.
>
> Another talk show this week, completely devoid of any current science.

This week, first half a return to the traditional science reporting
format, excellent; second half a stilted, contrived 'conversation'*
about what was in science news this week, followed by vacuous crap in
which Helen Keen took several minutes of irrelevant nothingness finally
to tell us that we should grind our coffee coarsely, which information
and the reasons thereof could have been conveyed in a few seconds.

* Why is that these days so much radio and tv output is filled with
these irritatingly unrealistic fake and halting 'conversations' instead
of just allowing someone who knows a thing or two to spend a few minutes
explaining it to us fluently in their own words?

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

In article <u4ofbr$3lf8o$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:

> * Why is that these days so much radio and tv output is filled with
> these irritatingly unrealistic fake and halting 'conversations' instead
> of just allowing someone who knows a thing or two to spend a few minutes
> explaining it to us fluently in their own words?

Modern attempt by the BBC to "Get down wiv da Yoof." perhaps? i.e. assume a
radio program has to emulate anti-social meeja?

I tend to listen to progs a few weeks after broadcast as I select them from
BBC iPlayer pages. So haven't yet hit some of the item commented on in this
thread, though.

Been busy with:

1) Going though a "gasman cometh" series of various trades-blokes making
changes/fixes to our house... and in the process creating new flaws that
require someone else, later, to come and fix. In the process, producing a
new flaw... loop until.

2) Trying to analyse data on the sheer scale and reliability of the wind
energy potential of the UK/Scottish EEZ at sea. Which real data seems to
show is very large indeed!

If anyone is curious about (2), this page
https://globalwindatlas.info/en
provides quite a nice interactive map where you can check the data.

There is also a BIG archive of open sourced measured data for the relevant
areas. Alas, it is well over 1 TB so too big for me to fetch here. So I'm
going to see if I can contact the providers to arrange a sneakernet
approach. Or ask someone at my old Uni to act as an intermediate fetcher to
someting like a sized USB HD.

Jim

Jim

--
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On 23/05/2023 13:34, Java Jive wrote:
> On 23/05/2023 11:18, Vir Campestris wrote:
>> On 18/05/2023 16:37, Java Jive wrote:
>>> On 18/05/2023 12:55, #Paul wrote:
>>>>
>>>> Java Jive <java@evij.com.invalid> wrote:
>>>>>
>>>>> The error is that the law of conservation of momentum only applies
>>>>> with
>>>>> 'perfectly' elastic collisions, ...
>>>>
>>>> Assuming translational invariance, conservation of momentum always
>>>> applies (although sometimes momentum can hide in odd places).
>>>
>>> Yes, my mistake, it's kinetic energy that is not conserved  -
>>> Applied Maths & Physics A-Levels were a very long time ago.
>>>
>>> However, I think my description of what was happening in the video
>>> clips is still correct, and I note that, so far at least, you haven't
>>> questioned that.
>>>
>> You said "Because conservation of momentum does not apply"
>>
>> I disagree with that statement. Conservation of momentum always applies.
>
> Which I have admitted was an error, but in the quote above you have
> conveniently omitted the fact that I then continued ...
>
> "to understand what's really going on, you have to understand what's
> happening to the kinetic energy of the impact.  In both cases, while
> some of it is transmitted through the medium into downwards momentum of
> its container, a significant proportion of it is also lost as heat,
> sound, and distortion of the medium surface, but the crucial point is
> that, because the two mediums have different elasticities, different
> amounts of it is being so transmitted and lost in the two cases."
>
> ... and all that is true.
>
This time I'm going to quote you in full.

The reason I cut out the words on kinetic energy is that they are
irrelevant.

It is the conservation of momentum that matters. Only that.

>> In the wet sand case after the collision we have effectively a single
>> mass.
>>
>> In the loose gravel case we have
>> * A large mass of the bucket and the ball
>> * A smaller mass of the "splashed" gravel which is moving upwards.
>>
>> The splashed gravel has "negative" (upwards) momentum; which means the
>> ball-and-bucket will have more "positive" (downwards) momentum.
>
> As already explained, both differences in behaviour  -  the greater
> downward movement and the greater upward movement  -  are both *EFFECTS*
> of the differing properties of the two mediums, so neither can be the
> cause, and therefore also not the explanation, of the other.  So far,
> I've mentioned elasticity, but actually there are at least two more
> properties of the mediums which are as or more important:
>
> *  The differing densities of the two mediums.  Watching the clips,
> although it's difficult to be sure, I think what was going on was that
> two identical containers were filled nearly to the brim with the two
> mediums, so the volume of material was constant for the two experiments,
> but their differing densities would then mean that in the first
> experiment the momentum imparted by the ball is being applied to a
> larger mass than in the second, so you'd expect a smaller displacement
> of the target for the first and a larger for the second, regardless of
> any other considerations.
>
> *  The wet sand is held together by surface tension of the water between
> the grains, and therefore is more self-cohesive, and therefore more
> difficult to distort the surface of, and hence more kinetic energy is
> lost in doing so, whereas the pseudo-regolith is less self-cohesive,
> much more easily distorted, and therefore less kinetic energy is lost in
> doing so.
>
> So the situation is much more complex than implied in the clip, and
> regardless of whichever of these three properties is predominant in
> effect, the term 'momentum enhancement' seems to me to be quite wrong
> for describing what is going on.
>

That term made perfect sense to me, even though I had never heard it before.

Andy

On 26/05/2023 20:42, Vir Campestris wrote:
>
> On 23/05/2023 13:34, Java Jive wrote:
>>
>> So the situation is much more complex than implied in the clip, and
>> regardless of whichever of these three properties is predominant in
>> effect, the term 'momentum enhancement' seems to me to be quite wrong
>> for describing what is going on.
>
> That term made perfect sense to me, even though I had never heard it
> before.

It's an inherent self-contradiction: How can momentum be 'enhanced' if
it's preserved?

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

On 26/05/2023 21:37, Java Jive wrote:
> On 26/05/2023 20:42, Vir Campestris wrote:
>>
>> On 23/05/2023 13:34, Java Jive wrote:
>>>
>>> So the situation is much more complex than implied in the clip, and
>>> regardless of whichever of these three properties is predominant in
>>> effect, the term 'momentum enhancement' seems to me to be quite wrong
>>> for describing what is going on.
>>
>> That term made perfect sense to me, even though I had never heard it
>> before.
>
> It's an inherent self-contradiction: How can momentum be 'enhanced' if
> it's preserved?
>
A small object hits the target asteroid, and transfers its momentum.

It hits it so hard that some debris is splashed backwards, as it would
be if it landed in water.

That debris has momentum in the opposite direction to the projectile.

Because the impact pushed debris in the opposite direction to the
projectile the momentum of the target has changed more than it would
from just the projectile.

Andy

On 28/05/2023 21:13, Vir Campestris wrote:
> On 26/05/2023 21:37, Java Jive wrote:
>> On 26/05/2023 20:42, Vir Campestris wrote:
>>>
>>> On 23/05/2023 13:34, Java Jive wrote:
>>>>
>>>> So the situation is much more complex than implied in the clip, and
>>>> regardless of whichever of these three properties is predominant in
>>>> effect, the term 'momentum enhancement' seems to me to be quite
>>>> wrong for describing what is going on.
>>>
>>> That term made perfect sense to me, even though I had never heard it
>>> before.
>>
>> It's an inherent self-contradiction: How can momentum be 'enhanced' if
>> it's preserved?
>
> A small object hits the target asteroid, and transfers its momentum.
>
> It hits it so hard that some debris is splashed backwards, as it would
> be if it landed in water.
>
> That debris has momentum in the opposite direction to the projectile.
>
> Because the impact pushed debris in the opposite direction to the
> projectile the momentum of the target has changed more than it would
> from just the projectile.

So momentum has been preserved, not enhanced.

[And, as already explained, both effects arise from properties of the
medium impacted, so neither can be considered the cause of the other.]

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

On 28/05/2023 22:57, Java Jive wrote:
> On 28/05/2023 21:13, Vir Campestris wrote:
>> On 26/05/2023 21:37, Java Jive wrote:
>>> On 26/05/2023 20:42, Vir Campestris wrote:
>>>>
>>>> On 23/05/2023 13:34, Java Jive wrote:
>>>>>
>>>>> So the situation is much more complex than implied in the clip, and
>>>>> regardless of whichever of these three properties is predominant in
>>>>> effect, the term 'momentum enhancement' seems to me to be quite
>>>>> wrong for describing what is going on.
>>>>
>>>> That term made perfect sense to me, even though I had never heard it
>>>> before.
>>>
>>> It's an inherent self-contradiction: How can momentum be 'enhanced'
>>> if it's preserved?
>>
>> A small object hits the target asteroid, and transfers its momentum.
>>
>> It hits it so hard that some debris is splashed backwards, as it would
>> be if it landed in water.
>>
>> That debris has momentum in the opposite direction to the projectile.
>>
>> Because the impact pushed debris in the opposite direction to the
>> projectile the momentum of the target has changed more than it would
>> from just the projectile.
>
> So momentum has been preserved, not enhanced.
>

What they are intending to say is that the change of momentum of the
asteroid is greater than you get from the momentum of the projectile.

It's just semantics really!

> [And, as already explained, both effects arise from properties of the
> medium impacted, so neither can be considered the cause of the other.]
>
Agreed.

Andy

On 29/05/2023 11:21, Vir Campestris wrote:
>
> On 28/05/2023 22:57, Java Jive wrote:
>>
>> So momentum has been preserved, not enhanced.
>
> What they are intending to say is that the change of momentum of the
> asteroid is greater than you get from the momentum of the projectile.

Impossible, because then momentum would have been created, not preserved!

> It's just semantics really!

Semantics are important in science, and their poor use of words are
exactly what gave rise to my original complaint!

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

On Fri, 26 May 23 09:45:02 UTC, Jim Lesurf <noise@audiomisc.co.uk> wrote:

> 1) Going though a "gasman cometh" series of various trades-blokes making
> changes/fixes to our house... and in the process creating new flaws that
> require someone else, later, to come and fix. In the process, producing a
> new flaw... loop until.

Mine went straight from Monday to Wednesday. Thankfully Tuesday and Thursday
never happened. Friday is still pending, which is probably down to me, but
really (a different) Monday needs to come back and sort out the f'ing mess,
so there is no point.

In article <u50io4$11hfv$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:
> > Because the impact pushed debris in the opposite direction to the
> > projectile the momentum of the target has changed more than it would
> > from just the projectile.

> So momentum has been preserved, not enhanced.

> [And, as already explained, both effects arise from properties of the
> medium impacted, so neither can be considered the cause of the other.]

However the desired outcome is momentum transfer (to the target)
'enhancement'. So perhaps "momentum transfer enhancement" is a fair term.
That said I suspect 'rocket scientists' would prefer "delta-V enhancement"
8-]

Jim

--
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In article <u5314r$1k8qs$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:
> > What they are intending to say is that the change of momentum of the
> > asteroid is greater than you get from the momentum of the projectile.

> Impossible, because then momentum would have been created, not preserved!

Note that momentum has a sign whereas kinetic energy does not. :-)

Jim

--
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In article <slrnu7ad07.3l2o.abuse@news.pr.network>, Paul Ratcliffe
<abuse@orac12.clara34.co56.uk78> wrote:
> On Fri, 26 May 23 09:45:02 UTC, Jim Lesurf <noise@audiomisc.co.uk> wrote:

> > 1) Going though a "gasman cometh" series of various trades-blokes
> > making changes/fixes to our house... and in the process creating new
> > flaws that require someone else, later, to come and fix. In the
> > process, producing a new flaw... loop until.

> Mine went straight from Monday to Wednesday. Thankfully Tuesday and
> Thursday never happened. Friday is still pending, which is probably down
> to me, but really (a different) Monday needs to come back and sort out
> the f'ing mess, so there is no point.

We now have some tradesmen on the roof fixing damaged/dislodged/ loose/etc
tiles... Next wll come housepainters if I can get them to give a quote for
the work we want, not the (larger amount of) work they want to do! Still
waiting for the man to come and fit new blinds in the kitchen. I'll
probably try to fix the hole in the bathroom wall myself as it is an
indoors job. (Hole left by 'plumbers' who needlessly moved the toilet and
regard filling holes as "someone else's job".)

Jim

--
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On 30/05/2023 09:45, Jim Lesurf wrote:
> In article <u5314r$1k8qs$1@dont-email.me>, Java Jive
> <java@evij.com.invalid> wrote:
>>> What they are intending to say is that the change of momentum of the
>>> asteroid is greater than you get from the momentum of the projectile.
>>
>> Impossible, because then momentum would have been created, not preserved!
>
> Note that momentum has a sign whereas kinetic energy does not. :-)

Yes, but I was merely pointing out that what he said, still quoted
above, was probably not what he meant to say!

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

On 30/05/2023 09:30, Jim Lesurf wrote:
>
> However the desired outcome is momentum transfer (to the target)
> 'enhancement'. So perhaps "momentum transfer enhancement" is a fair term.
> That said I suspect 'rocket scientists' would prefer "delta-V enhancement"
> 8-]

I don't think anyone's disputing what the intention is, merely the
unfortunately inaccurate term originally used to describe it.

Between us we've suggested several possible improvements now!

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On 30/05/2023 14:13, Java Jive wrote:
> On 30/05/2023 09:45, Jim Lesurf wrote:
>> In article <u5314r$1k8qs$1@dont-email.me>, Java Jive
>> <java@evij.com.invalid> wrote:
>>>> What they are intending to say is that the change of momentum of the
>>>> asteroid is greater than you get from the momentum of the projectile.
>>>
>>> Impossible, because then momentum would have been created, not
>>> preserved!
>>
>> Note that momentum has a sign whereas kinetic energy does not. :-)
>
> Yes, but I was merely pointing out that what he said, still quoted
> above, was probably not what he meant to say!
>

No, it is what I meant to say.

Let me give you a simile with numbers.

Suppose the asteroid has twice the mass of the projectile, and is still
from the viewpoint of the observer.

If the projectile hits and sticks then the combined mass will move away
with 1/3 of the velocity of the projectile.

If the projectile bounced back at the same speed it arrived, but in the
opposite direction, then its change of momentum would be twice as big.

(As I write that it occurs to me that is too big a change to be
possible, but it makes the maths work easily)

In addition the mass of the asteroid would not have increased.

So we would have twice the momentum of the projectile being transferred
to a lighter resulting mass, and the asteroid would be moving faster
than if the projectile stuck..

I'm sure given that you'll be able to work it through with bigger mass
difference and a smaller bounce. It doesn't matter if it's the
projectile that bounce, or some other part of the asteroid that moves
back in the direction the asteroid was moving.

Andy

On 30/05/2023 17:45, Vir Campestris wrote:
> On 30/05/2023 14:13, Java Jive wrote:
>> On 30/05/2023 09:45, Jim Lesurf wrote:
>>> In article <u5314r$1k8qs$1@dont-email.me>, Java Jive
>>> <java@evij.com.invalid> wrote:
>>>>> What they are intending to say is that the change of momentum of the
>>>>> asteroid is greater than you get from the momentum of the projectile.
>>>>
>>>> Impossible, because then momentum would have been created, not
>>>> preserved!
>>>
>>> Note that momentum has a sign whereas kinetic energy does not. :-)
>>
>> Yes, but I was merely pointing out that what he said, still quoted
>> above, was probably not what he meant to say!
>>
>
> No, it is what I meant to say.
>
> Let me give you a simile with numbers.
>
> Suppose the asteroid has twice the mass of the projectile, and is still
> from the viewpoint of the observer.
>
> If the projectile hits and sticks then the combined mass will move away
> with 1/3 of the velocity of the projectile.
>
> If the projectile bounced back at the same speed it arrived, but in the
> opposite direction, then its change of momentum would be twice as big.
>
> (As I write that it occurs to me that is too big a change to be
> possible, but it makes the maths work easily)

And that's the problem ...

Quote: "the change of momentum of the asteroid is greater than you get
from the momentum of the projectile", which is impossible, because then
you would have created momentum out of nothing. The *maximum* change of
momentum that can be transferred to the asteroid by the collision is the
total momentum of the projectile just before impact, and for this to
happen, both asteroid and projectile would have to be perfectly elastic,
which would result in the projectile stopping at the impact point, and
the asteroid being 'cannoned' forward along the original path of the
projectile with the maximum velocity possible given their relative masses.

But I think you should forget about the momentum; it seems to be
confusing you, and the more we discuss it, the more I become convinced
that the greater displacement in the second experiment was almost
entirely, or indeed entirely, due to the medium being less dense, and
therefore the same volume of it to fill the container had less mass,
than the wet sand medium in the first experiment; that in itself would
explain its greater displacement, and, actually, that is the *only* way
I can explain the greater displacement of the second experiment using
conservation of momentum alone.

I think you might find it easier to think about the kinetic energy
involved. Kinetic energy is only completely retained in a perfectly
elastic collision, in any collision less than perfectly elastic kinetic
energy is lost by conversion to other forms of energy such as heat. So
what they're trying to do is to maximise the retention of kinetic energy
by aiming at those types of asteroid surface that are more elastic, and
avoiding surfaces that are less elastic.

--

Fake news kills!

I may be contacted via the contact address given on my website:
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In article <u560kk$24nnv$1@dont-email.me>, Java Jive
<java@evij.com.invalid> wrote:
> And that's the problem ...

> Quote: "the change of momentum of the asteroid is greater than you get
> from the momentum of the projectile", which is impossible, because then
> you would have created momentum out of nothing.

Momentum has a sign. So a bounce back has a 'negative' momentum.

Jim

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On 01/06/2023 09:45, Jim Lesurf wrote:
>
> In article <u560kk$24nnv$1@dont-email.me>, Java Jive
> <java@evij.com.invalid> wrote:
>>
>> And that's the problem ...
>
>> Quote: "the change of momentum of the asteroid is greater than you get
>> from the momentum of the projectile", which is impossible, because then
>> you would have created momentum out of nothing.
>
> Momentum has a sign. So a bounce back has a 'negative' momentum.

Jim, I'm surprised at you. Consider ...

In both experiments, to within suitable accuracy, the ball is dropped
from the same height, accelerates under gravity, and its mass Mb strikes
the surface with the same velocity Vb. So in both cases the momentum of
the ball just before it strikes the surface is Mb*Vb.

During both impacts, while they are actually occurring, the surface of
the medium is momentarily disturbed although by differing amounts and in
different ways - the surface material is pushed or flung about,
including upwards, but then comes to rest back on the back on the now
distorted surface.

After both impacts the entire 'scale' assembly is moving downwards at
different speeds, which we shall call Vs for the sand experiment and Vr
for the pseudo-regolith experiment. Let us also call M the unchanging
part of the mass of the 'scale' - the springs, containers, etc - and
Ms and Mr the masses of the sand and regolith in the scale, which, for
the experiment to be done properly, ought to be the same. However, the
video suggests that this is not so, and in fact conservation of momentum
proves they are different, as follows:

Momentum before each impact: Mb*Vb
Momentum after sand impact: (M + Mb + Ms)*Vs
Momentum after regolith impact: (M + Mb + Mr)*Vr

So conservation of momentum gives us two equations ...

Mb*Vb = (M + Mb + Ms)*Vs
Mb*Vb = (M + Mb + Mr)*Vr

.... from which it is trivial to show that ...

(M + Mb + Ms)*Vs = (M + Mb + Mr)*Vr

.... and equally trivially that if, as was the case, ...

Vs <> Vr

.... the only way the last equation above can hold true is if also ...

Ms <> Mr

.... but the formal mathematical way of showing this is to show that if
we assume that Ms = Mr then it leads to a contradiction:

Let Ma = M + Mb + Ms = M + Mb + Mr. Then we have

Ma*Vs = Ma*Vr

.... cancelling the masses giving us ...

Vs = Vr

.... which contradicts the observed results, showing that our assumption
that Ms = Mr was wrong.

So the different final velocities in the two experiments was caused by
the different masses of the mediums.

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Fake news kills!

I may be contacted via the contact address given on my website:
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