Physics Quiz...

[Ricky]

On Tuesday, April 25, 2023 at 5:50:35 AM UTC-4, Martin Brown wrote:

Conservation of angular momentum is more fundamental here which means
that she spins much faster with arms in (and with more stored energy).
Choosing the correct conservation law is essential!

LOL! Which laws can be ignored? NONE!

You do the calculations with the knowledge that all physical laws are active, conservation of momentum and energy. There\'s no value to the idea that one of the two laws \"is more fundamental\".

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[Martin Brown]

On 26/04/2023 13:43, Carlos E.R. wrote:

On 2023-04-26 12:01, Clive Arthur wrote:
On 25/04/2023 18:16, RichD wrote:

snip

It\'s too complicated to derive the exact road speed as a function
of rotational speed, for this irregular shape.  Simplify it: the tire
is a clock face.  12 o\'clock moves at the same speed as (flattened) 6
o\'clock.

No, it doesn\'t.  The 12 o\'clock radius is greater than the 6 o\'clock
radius, so its speed is greater.

Maybe that\'s not immediately obvious to you, but consider that the 6
o\'clock portion (and a bit either side) is taking an enforced short
cut along a straight line, the road surface, whereas the 12 o\'clock
portion is going the longer way around the circumference of a circle.

Ok, so that means that the speed of the surface of the wheel at any
point that is not under the vehicle weight is actually greater than the
road or vehicle speed. Thus when the wheel is released from the car, it
really is turning faster than previous speed.

It isn\'t turning any faster but once free it is turning around an axis
that has moved upwards by 1-2cm out of perhaps a nominal 30cm radius.

Equivalent to a ~3% increase in linear speed.

So that\'s it.

--
Martin Brown

 

[RichD]

On April 26, Fred Bloggs wrote:

The external forces are REACTION forces, as the axle drives the wheels.
They aren\'t a power supply! When the wheel detaches, it\'s a free body,
it doesn\'t magically accelerate due to imaginary forces.

If you look at the free body diagram of the whole vehicle in steady state
without acceleration, you can see the horizontal component of the tire/
road reaction force exactly equals the wind resistance force acting on
the vehicle, plus the force necessary to push the tire off the flat spot,
That same force is what gives the tire its acceleration when it\'s free.

uh huh
When the wheel is NOT DRIVEN by the axle, it ACCELERATES -

https://www.pinterest.co.uk/pin/705728204100124792/

--
Rich

 

[Tabby]

On Tuesday, 25 April 2023 at 02:38:31 UTC+1, Ricky wrote:

On Sunday, April 23, 2023 at 7:36:36 PM UTC-4, Tabby wrote:
On Sunday, 23 April 2023 at 23:48:05 UTC+1, John Larkin wrote:
On Sun, 23 Apr 2023 15:30:24 -0400, bitrex <us...@example.net> wrote:

On 4/23/2023 8:44 AM, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:
So a vehicle is driving down the road when an entire wheel comes off and continues its direction unchanged rolling alongside the vehicle. Question is why does the wheel end up accelerating, rolling much faster than its original speed, outpacing the vehicle significantly? Answer should be obvious, but you need practical insight.
The only thing that could accelerate it would be the airflow around the vehicle body, which would be associated with trailing vortices.

It seems unlikely than any of them could make the wheel rotate much faster than it\'s original speed - it would outrun the car and the trailing vortices - unless it was moving sideways with respect to the rest of the car, and out into the wake.

Alright, you\'re getting close. From what I\'ve personally observed, a wheel dropping off the vehicle leaves the vehicle behind in the dust, it really takes off.

It seems like a potentially complex process, particularly if it\'s one of
the drive wheels in a modern car with traction control, and/or the wheel
isn\'t in full contact with the pavement when it separates.
If it bounces up before it breaks off, the differential (assume it has
one) could spin it way up.
And no mention yet of the fact that the last bolt to let go is going to put force on the tyre in some direction. What direction I couldn\'t say.
It\'s too complex to analyze.
+1

We have video. Mostly, the wheel shot sideways like it was on a rocket. But that was because the car hit it before it could make significant contact with the road.

I really don\'t see the bolts having much to do with it. Maybe you are not aware that there is a hole in the wheel that fits over the hub. Even when all the bolts break or the nuts are unscrewed, the wheel still has to come off the hub.

I assume the time between last bolt letting go and wheel disenaging completely is anything from zero to very short. Which is the last bit to let go, hub or bolt, I can\'t say. Have you tested that? If the hub let go later than the bolt, the resulting final force on the wheel would generally be sideways, but most tyre loss videos show no sign of significant sideways force in the tyre\'s trajectory. That leads me to conclude, albeit uncertainly, that it\'s the bolt that is the last to let go. Do you have something better?

 

[Martin Brown]

On 26/04/2023 16:23, Ricky wrote:

On Tuesday, April 25, 2023 at 5:50:35 AM UTC-4, Martin Brown wrote:

Conservation of angular momentum is more fundamental here which
means that she spins much faster with arms in (and with more stored
energy). Choosing the correct conservation law is essential!

LOL! Which laws can be ignored? NONE!

I didn\'t say ignore. I said choose wisely which conservation law you
apply to make the solution more easily accessible with less work.

You do the calculations with the knowledge that all physical laws are
active, conservation of momentum and energy. There\'s no value to the
idea that one of the two laws \"is more fundamental\".

The point here is that using conservation of energy requires doing some
nasty integrals of the forces and torques acting on the ballet dancers
arms as she moves them. You would get the same result using conservation
of energy if you did that calculation but it is much more difficult.

You can get to the right answer a lot more easily by applying the law of
conservation of angular momentum to starting and end configurations. And
for good measure work out the system energy in each state too.

--
Martin Brown

 

[Martin Brown]

On 24/04/2023 23:45, RichD wrote:

On April 23, John Larkin wrote:
So a vehicle is driving down the road when an entire wheel comes off
and continues its direction unchanged rolling alongside the vehicle.
Question is why does the wheel end up accelerating, rolling much faster
than its original speed, outpacing the vehicle significantly?

A wheel can store energy in the rubber. Before it was turned loose,
there was torque, which flexed the rubber.

The continuous torque is what rotates the wheel, against
losses. It the torque is removed, it slows. (!!)

That much is true. But the wheel was previously being driven by the
engine and so the tyre wall has stored elastic energy in it that will be
released when the wheel breaks free and it will continue to provide a
torque until the wheel starts to slip or leaves contact with the ground.
In the air it will encounter no rolling resistance at all, but any
residual stored energy in the tyre wall is lost at that point.

And compression.

The compression is the flattened portion, against the road.
Weight and gravity. When it decompresses, it bounces straight
up. No torque.

If the car was coasting in neutral when the wheel broke free then you
would be right but if it was accelerating then there is stored energy in
the tyre wall that can provide some modest acceleration after it parts
company with the car.

Likewise if the car was braking hard then there would be elastic
deformation of the tyre wall that would tend to decelerate it after it
broke free.

Most of the change of apparent linear speed comes from the effective
radius of the tyre increasing when the load of the car is removed. My
thick wall rigid runflats this would be about 1cm on 30cm radius tyres
~3% but on a conventional tyre underinflated it might be twice that.

--
Martin Brown

 

[Fred Bloggs]

On Wednesday, April 26, 2023 at 11:35:51 AM UTC-4, Ricky wrote:

On Wednesday, April 26, 2023 at 7:37:29 AM UTC-4, Fred Bloggs wrote:
On Tuesday, April 25, 2023 at 4:14:00 PM UTC-4, Martin Brown wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09 AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16 AM UTC-4, Martin Brown
wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24 AM UTC-4, Anthony
William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07 PM UTC+10, Fred
Bloggs wrote:
So a vehicle is driving down the road when an entire
wheel comes off and continues its direction unchanged
rolling alongside the vehicle. Question is why does the
wheel end up accelerating, rolling much faster than its
original speed, outpacing the vehicle significantly?
Answer should be obvious, but you need practical
insight.
The only thing that could accelerate it would be the
airflow around the vehicle body, which would be associated
with trailing vortices.

It seems unlikely than any of them could make the wheel
rotate much faster than it\'s original speed - it would
outrun the car and the trailing vortices - unless it was
moving sideways with respect to the rest of the car, and
out into the wake.

Alright, you\'re getting close. From what I\'ve personally
observed, a wheel dropping off the vehicle leaves the
vehicle behind in the dust, it really takes off.

Its diameter changes quite radically when it is no longer
being squashed by the weight of the car and so although it was
previously rolling with constant velocity at radius r when
loaded the sudden loss of load means the tyre expands to about
10-15% larger radius R ~ 1.1r where it is in contact with the
road. The car may also slow down with one wheel missing if the
driver has any road sense at all.

Angular momentum is conserved in the short term so the wheel
now has a linear velocity increase by about 10-15% compared to
the car.

Doesn\'t the increased radius increase the angular moment of
inertia about the centroid, thereby slowing the rotational speed
to conserve angular momentum? But you hit on one of two causes
for speed increase. Having the weight of the vehicle suddenly
removed means the effective friction between the tire and the
road, caused by having to overcome that weighted flat spot where
road and tread meets, is completely eliminated. The flat spot
effect has been traditionally modelled as continuously have to
apply translational force to push the tire out of a rut the depth
of the flat spot. These days they probably use finite element
analysis to make it more accurate, but that\'s essentially it.
The change in moment of inertia is rather small though.
But it doesn\'t explain the increase in rotational speed.
I\'m not sure that there is an increase rotational speed merely an
increase in the effective diameter of the wheel - which separates
from the vehicle with linear speed v and initial radius r. The
rebound of the tyre when the load is removed will make it bounce
into the air as JL pointed out and then the new diameter of the
tyre R where it is only supporting its own weight comes into play.


In the few I\'ve seen in traffic, the wheel comes off, races in front
of the car that lost it, and catches up with the cars in front of it,
with those cars moving at constant speed. I don\'t see any other way
to interpret that other than the wheel picked up speed.

I think it stems from the sudden change in effective diameter when the
tyre is no longer under full load of the vehicle weight.
I only know of one hapless individual with no engineering or
mechanical sense at all who was actually passed by one of their
own wheels.

Worst thing is when they bounce into oncoming traffic, which
almost always causes a serious wreck. Or they could hit a
pedestrian on a sidewalk, which almost always kills them.
Does this happen a lot in the USA?

Probably because U.S. has so many more cars on the road than anyplace
else...

ITYM so many *badly maintained* vehicles.
U.S. has an annual inspection requirement,
Pure fantasy. The US government has virtually nothing to do with auto inspections. That is handled at the state level, where some states have an annual inspection, and some don\'t. Virginia used to have an inspection every 6 months! Maryland has mandatory inspections, ONLY when a car trades hands.

As usual you don\'t know what you\'re talking about. The federal government did in fact require nationwide vehicle inspections under the authority of the Clean Air Act. A subsequent Highway Safety Act in the 80s did away with the requirement. A lot of states immediately dropped their inspections at that point, but a lot of them still hung on to them into the 2000s. Recent U.S. highway safety data is showing fatalities due to equipment failure is in the 10 ppm range and therefore not worth the enormous cost to consumers, causing even more states to drop the requirement.

The only interesting part of this discussion is the seemingly universal threshold of 10-ish ppm to disregard any proximal cause of adverse events.

and the inspection has to be performed by a state licensed inspector. Some of them are really thorough, they look at several dozen parts, and check off their work as they go. And the car gets a windshield sticker, without which or expired, the driver gets a fairly hefty fine- at least 3x the cost of getting the inspection.
Maryland has no sticker. They rely on cops observing defects and issuing inspection tickets. So this typically only impacts lights and exhaust systems, resulting in some number of unsafe vehicles being on the road until they are in accidents!

Not real concerned about the particulars of Maryland\'s vehicle inspection system...

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209

 

[John Larkin]

On Thu, 27 Apr 2023 12:43:04 +0200, \"Carlos E.R.\"
<robin_listas@es.invalid> wrote:

On 2023-04-26 17:31, Anthony William Sloman wrote:
On Thursday, April 27, 2023 at 1:14:36?AM UTC+10, John Larkin wrote:
On Tue, 25 Apr 2023 21:13:50 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09?AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16?AM UTC-4, Martin Brown wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:

snip

Probably because U.S. has so many more cars on the road than anyplace else...

ITYM so many *badly maintained* vehicles.
It\'s very rare to see a junker here. Not 1 in 100. It\'s also rare to see a Ford (Found On Road, Dead.)

Many US states have periodic vehicle inspection, but that doesn\'t involve disassembling and inspecting wheel bearings. Do you regularly inspect your wheel bearings?

It\'s impressive how much ignorance-driven anti-Americanism there is.

It\'s even more impressive how John Larkin can find it when it isn\'t actually there.

Right.

MB claimed the US has \"so many *badly maintained* vehicles\"

He also told me what I meant. Which of course I didn\'t.

Isn\'t he British? Should I note that all Brits are rude jerks who
design bad electronics? No, I\'m to polite.

 

[Martin Brown]

On 27/04/2023 17:54, John Larkin wrote:

On Thu, 27 Apr 2023 12:43:04 +0200, \"Carlos E.R.\"
robin_listas@es.invalid> wrote:

On 2023-04-26 17:31, Anthony William Sloman wrote:
On Thursday, April 27, 2023 at 1:14:36?AM UTC+10, John Larkin wrote:
On Tue, 25 Apr 2023 21:13:50 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09?AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16?AM UTC-4, Martin Brown wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:

snip

Probably because U.S. has so many more cars on the road than anyplace else...

ITYM so many *badly maintained* vehicles.
It\'s very rare to see a junker here. Not 1 in 100. It\'s also rare to see a Ford (Found On Road, Dead.)

Many US states have periodic vehicle inspection, but that doesn\'t involve disassembling and inspecting wheel bearings. Do you regularly inspect your wheel bearings?

It\'s impressive how much ignorance-driven anti-Americanism there is.

It\'s even more impressive how John Larkin can find it when it isn\'t actually there.

Right.



MB claimed the US has \"so many *badly maintained* vehicles\"

He also told me what I meant. Which of course I didn\'t.

Isn\'t he British? Should I note that all Brits are rude jerks who
design bad electronics? No, I\'m to polite.

And illiterate.

--
Martin Brown

 

[John Larkin]

On Thu, 27 Apr 2023 19:11:34 +0100, Martin Brown
<\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 27/04/2023 17:54, John Larkin wrote:
On Thu, 27 Apr 2023 12:43:04 +0200, \"Carlos E.R.\"
robin_listas@es.invalid> wrote:

On 2023-04-26 17:31, Anthony William Sloman wrote:
On Thursday, April 27, 2023 at 1:14:36?AM UTC+10, John Larkin wrote:
On Tue, 25 Apr 2023 21:13:50 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09?AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16?AM UTC-4, Martin Brown wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:

snip

Probably because U.S. has so many more cars on the road than anyplace else...

ITYM so many *badly maintained* vehicles.
It\'s very rare to see a junker here. Not 1 in 100. It\'s also rare to see a Ford (Found On Road, Dead.)

Many US states have periodic vehicle inspection, but that doesn\'t involve disassembling and inspecting wheel bearings. Do you regularly inspect your wheel bearings?

It\'s impressive how much ignorance-driven anti-Americanism there is.

It\'s even more impressive how John Larkin can find it when it isn\'t actually there.

Right.



MB claimed the US has \"so many *badly maintained* vehicles\"

He also told me what I meant. Which of course I didn\'t.

Isn\'t he British? Should I note that all Brits are rude jerks who
design bad electronics? No, I\'m to polite.

And illiterate.

I read a lot, at about 400 WPM. I don\'t type or spell well and, in
informal situations, don\'t care. I\'m very careful with manuals and
customer emails, but not in newsgroups full of mostly nasty people.

My real medium is schematics. You might google the term.

 

[Carlos E.R.]

On 2023-04-27 18:54, John Larkin wrote:

On Thu, 27 Apr 2023 12:43:04 +0200, \"Carlos E.R.\" <robin_listas@es.invalid> wrote:
On 2023-04-26 17:31, Anthony William Sloman wrote:
On Thursday, April 27, 2023 at 1:14:36?AM UTC+10, John Larkin wrote:
On Tue, 25 Apr 2023 21:13:50 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09?AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16?AM UTC-4, Martin Brown wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:

snip

Probably because U.S. has so many more cars on the road than anyplace else...

ITYM so many *badly maintained* vehicles.
It\'s very rare to see a junker here. Not 1 in 100. It\'s also rare to see a Ford (Found On Road, Dead.)

Many US states have periodic vehicle inspection, but that doesn\'t involve disassembling and inspecting wheel bearings. Do you regularly inspect your wheel bearings?

It\'s impressive how much ignorance-driven anti-Americanism there is.

It\'s even more impressive how John Larkin can find it when it isn\'t actually there.

Right.



MB claimed the US has \"so many *badly maintained* vehicles\"

Certainly. I see those in the movies

And I have personally seen them in Ottawa. They have some sort of
mandatory inspection when selling a car, they told me.

--
Cheers, Carlos.

 

[Tabby]

On Thursday, 27 April 2023 at 19:38:44 UTC+1, John Larkin wrote:

> My real medium is schematics. You might google the term.

I have googled terms like this before. Among reasonable boring circuits some oddities show up, including on occasion ones that make zero sense.

If you want to know a subject area thoroughly, doing this should not be overlooked, despite all the uninspiring stuff there are always oddities that don\'t make textbooks, academic discussions etc.

I apologise for bringing it back on topic.

 

[RichD]

On April 27, Martin Brown wrote:

A wheel can store energy in the rubber. Before it was turned loose,
there was torque, which flexed the rubber.

The continuous torque is what rotates the wheel, against
losses. It the torque is removed, it slows. (!!)

And compression.

The compression is the flattened portion, against the road.
Weight and gravity. When it decompresses, it bounces straight
up. No torque.

If the car was coasting in neutral when the wheel broke free then you
would be right but if it was accelerating then there is stored energy in
the tyre wall that can provide some modest acceleration after it parts
company with the car.
Likewise if the car was braking hard then there would be elastic
deformation of the tyre wall that would tend to decelerate it after it
broke free.

Your analysis is flawed. The stored energy in the rubber doesn\'t manifest
as kinetic energy of rotation.

As the vehicle rolls, and even more when it accelerates, there is continuous
compression at the line across the tire, where it meets the road. This
action stores potential energy in the material.

But it\'s the pressure of compression, it has no preferred direction, no net
torque on the tire. Torque arises ONLY from the axle\'s turn. When the
wheel breaks off, that disappears, there\'s no external power supply or torque.

A freestanding rotating object cannot generate a net torque... except when
it can. That is, if it has internal moving parts and battery. Insert mice
on paddle wheels inside a hollow wheel, they can generate a torque on the
wheel (which generates equal torque on them, Newton\'s third).

Fortunately or not, Goodyear doesn\'t plant mice inside their tires. And the
compressed rubber doesn\'t mimic them.

When the rubber snaps back to circular, the potential energy converts first
into kinetic energy (of the surface material), then heat. It doesn\'t convert
into rotational energy, it has no preferred direction. Your idea of acceleration
is an illusion of relative tire/road motion.

Most of the change of apparent linear speed comes from the effective
radius of the tyre increasing when the load of the car is removed. My
thick wall rigid runflats this would be about 1cm on 30cm radius tyres
~3% but on a conventional tyre underinflated it might be twice that.

When the tire suddenly inflates, and circumference increases, as the load
disappears, its moment of inertia will suddenly increase. If rpm is unchanged,
while the moment increases, there would be an increase in angular
momentum. I believe nature would frown on that -

Both effects (circumference and moment) are small, but angular velocity
must slightly diminish.

--
Rich

 

[John Larkin]

On Thu, 27 Apr 2023 15:05:33 -0700 (PDT), Tabby <tabbypurr@gmail.com>
wrote:

On Thursday, 27 April 2023 at 19:38:44 UTC+1, John Larkin wrote:

My real medium is schematics. You might google the term.

I have googled terms like this before. Among reasonable boring circuits some oddities show up, including on occasion ones that make zero sense.

To me, one important aspect of a schematic, or a PCB layout, is style
and form and beauty. Beautiful schematics work better.

 

[John Larkin]

On Thu, 27 Apr 2023 23:30:39 +0200, \"Carlos E.R.\"
<robin_listas@es.invalid> wrote:

On 2023-04-27 18:54, John Larkin wrote:
On Thu, 27 Apr 2023 12:43:04 +0200, \"Carlos E.R.\" <robin_listas@es.invalid> wrote:
On 2023-04-26 17:31, Anthony William Sloman wrote:
On Thursday, April 27, 2023 at 1:14:36?AM UTC+10, John Larkin wrote:
On Tue, 25 Apr 2023 21:13:50 +0100, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
On 24/04/2023 18:34, Fred Bloggs wrote:
On Monday, April 24, 2023 at 5:24:09?AM UTC-4, Martin Brown wrote:
On 23/04/2023 23:17, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 9:39:16?AM UTC-4, Martin Brown wrote:
On 23/04/2023 13:44, Fred Bloggs wrote:
On Sunday, April 23, 2023 at 7:49:24?AM UTC-4, Anthony William Sloman wrote:
On Sunday, April 23, 2023 at 9:01:07?PM UTC+10, Fred Bloggs wrote:

snip

Probably because U.S. has so many more cars on the road than anyplace else...

ITYM so many *badly maintained* vehicles.
It\'s very rare to see a junker here. Not 1 in 100. It\'s also rare to see a Ford (Found On Road, Dead.)

Many US states have periodic vehicle inspection, but that doesn\'t involve disassembling and inspecting wheel bearings. Do you regularly inspect your wheel bearings?

It\'s impressive how much ignorance-driven anti-Americanism there is.

It\'s even more impressive how John Larkin can find it when it isn\'t actually there.

Right.



MB claimed the US has \"so many *badly maintained* vehicles\"

Certainly. I see those in the movies

Hollywood is all Porsches and Teslas and Land Rovers and Rolls. They
have to ship in beaters for making movies.

And I have personally seen them in Ottawa. They have some sort of
mandatory inspection when selling a car, they told me.

North and East they salt the roads, so everything rusts out.

 

[Martin Brown]

On 27/04/2023 23:15, RichD wrote:

On April 27, Martin Brown wrote:
A wheel can store energy in the rubber. Before it was turned loose,
there was torque, which flexed the rubber.

The continuous torque is what rotates the wheel, against
losses. It the torque is removed, it slows. (!!)

And compression.

The compression is the flattened portion, against the road.
Weight and gravity. When it decompresses, it bounces straight
up. No torque.

If the car was coasting in neutral when the wheel broke free then you
would be right but if it was accelerating then there is stored energy in
the tyre wall that can provide some modest acceleration after it parts
company with the car.
Likewise if the car was braking hard then there would be elastic
deformation of the tyre wall that would tend to decelerate it after it
broke free.

Your analysis is flawed. The stored energy in the rubber doesn\'t manifest
as kinetic energy of rotation.

As the vehicle rolls, and even more when it accelerates, there is continuous
compression at the line across the tire, where it meets the road. This
action stores potential energy in the material.

But it\'s the pressure of compression, it has no preferred direction, no net
torque on the tire. Torque arises ONLY from the axle\'s turn. When the
wheel breaks off, that disappears, there\'s no external power supply or torque.

So far so good. But you don\'t appear to understand the nature of an
elastic medium. In the same way that the weight of the car deforms the
tyre in contact with the road to flat, the frictional force that the
tyre exerts on the road to propel the car forwards distorts the tyre
wall sideways as a result. When the tyre is free at least some of that
stored elastic energy is available to be recovered. It probably isn\'t
all that much before the wheel loses traction and slips though.

A freestanding rotating object cannot generate a net torque... except when
it can. That is, if it has internal moving parts and battery. Insert mice
on paddle wheels inside a hollow wheel, they can generate a torque on the
wheel (which generates equal torque on them, Newton\'s third).

I the case of the tyre wall it is because a radial line drawn on the
static tyre is no longer exactly vertical when the tyre is delivering a
force onto the road.

Fortunately or not, Goodyear doesn\'t plant mice inside their tires. And the
compressed rubber doesn\'t mimic them.

It isn\'t the compression. It is the torque that twists the rubber walls
of the tyre due to conveying the force to accelerate the car forwards.
Like I said it probably isn\'t a big effect but it is there.

It can only have any effect whilst the tyre has traction on the ground
and the rebound of the vertical compression means that isn\'t very long.

When the rubber snaps back to circular, the potential energy converts first
into kinetic energy (of the surface material), then heat. It doesn\'t convert
into rotational energy, it has no preferred direction. Your idea of acceleration
is an illusion of relative tire/road motion.

That part doesn\'t, but in case you hadn\'t noticed tyres are 3D objects.

Most of the change of apparent linear speed comes from the effective
radius of the tyre increasing when the load of the car is removed. My
thick wall rigid runflats this would be about 1cm on 30cm radius tyres
~3% but on a conventional tyre underinflated it might be twice that.

When the tire suddenly inflates, and circumference increases, as the load
disappears, its moment of inertia will suddenly increase. If rpm is unchanged,
while the moment increases, there would be an increase in angular
momentum. I believe nature would frown on that -

The moment of inertia only increases by a tiny amount where the flat
part moves back out to full unloaded radius (roughly proportional to the
change in shape - which covers a very small part of the circumference).
It does slightly increase the moment of inertia but not by much.

Both effects (circumference and moment) are small, but angular velocity
must slightly diminish.

The angular velocity will slightly diminish but the change in effective
rolling diameter is sufficiently large that it wins hands down. The
linear speed of the tyre will increase to match the new diameter subject
and its rotation rate will slow to the constraint of conservation of
energy. The resulting equilibrium is the tyre after escape moves a bit
faster than the truck it fell off. I don\'t think it is by much.

--
Martin Brown

 

[Tabby]

On Friday, 28 April 2023 at 00:18:19 UTC+1, John Larkin wrote:

On Thu, 27 Apr 2023 15:05:33 -0700 (PDT), Tabby <tabb...@gmail.com
wrote:
On Thursday, 27 April 2023 at 19:38:44 UTC+1, John Larkin wrote:

My real medium is schematics. You might google the term.

I have googled terms like this before. Among reasonable boring circuits some oddities show up, including on occasion ones that make zero sense.

To me, one important aspect of a schematic, or a PCB layout, is style
and form and beauty. Beautiful schematics work better.

I\'ve seen some horrors, eg some radio circuits from the 1910s & 20s with a different supply line for each stage AND different ground lines for each, with all these & more crisscrossing in a cramped rat nest. I\'ll give them one thing though, if you\'re desperate to save tuppence on paper & foil the battery does work as decoupling capacitors. And I dislike multipagers where for no obvious reason they made it difficult to follow the interconnections.

 

[RichD]

On April 28, Martin Brown wrote:

A wheel can store energy in the rubber. Before it was turned loose,
there was torque, which flexed the rubber.

The continuous torque is what rotates the wheel, against
losses. It the torque is removed, it slows. (!!)

And compression.

The compression is the flattened portion, against the road.
Weight and gravity. When it decompresses, it bounces straight
up. No torque.

If the car was coasting in neutral when the wheel broke free then you
would be right but if it was accelerating then there is stored energy in
the tyre wall that can provide some modest acceleration after it parts
company with the car.
Likewise if the car was braking hard then there would be elastic
deformation of the tyre wall that would tend to decelerate it after it
broke free.

Your analysis is flawed. The stored energy in the rubber doesn\'t manifest
as kinetic energy of rotation.
As the vehicle rolls, and even more when it accelerates, there is continuous
compression at the line across the tire, where it meets the road. This
action stores potential energy in the material.

But it\'s the pressure of compression, it has no preferred direction, no net
torque on the tire. Torque arises ONLY from the axle\'s turn. When the
wheel breaks off, that disappears, there\'s no external power supply or torque.

So far so good. But you don\'t appear to understand the nature of an
elastic medium. In the same way that the weight of the car deforms the
tyre in contact with the road to flat, the frictional force that the
tyre exerts on the road to propel the car forwards distorts the tyre
wall sideways as a result. When the tyre is free at least some of that
stored elastic energy is available to be recovered.

A freestanding rotating object cannot generate a net torque... except when
it can. That is, if it has internal moving parts and battery. Insert mice
on paddle wheels inside a hollow wheel, they can generate a torque on the
wheel (which generates equal torque on them, Newton\'s third).

I the case of the tyre wall it is because a radial line drawn on the
static tyre is no longer exactly vertical when the tyre is delivering a
force onto the road.

Fortunately or not, Goodyear doesn\'t plant mice inside their tires.
And the compressed rubber doesn\'t mimic them.

It isn\'t the compression. It is the torque that twists the rubber walls
of the tyre due to conveying the force to accelerate the car forwards.
Like I said it probably isn\'t a big effect but it is there.

Perhaps I wasn\'t clear.

In addition to the radial compression due to weight, there is
another, circumferential compression, due to friction, where
rubber meets road. Which is your reference, above.

This stored energy doesn\'t produce torque after the wheel breaks
loose, doesn\'t accelerate rotation, it has no preferred direction.
Stretch a loop rubber band into a larger area. Release. No rotation,
no linear momentum. The stored energy acts on the molecules when
it shrinks, and they move; kinetic energy. After it shrinks to original
size, the energy dissipates as heat.

When the rubber snaps back to circular, the potential energy converts first
into kinetic energy (of the surface material), then heat. It doesn\'t convert
into rotational energy, it has no preferred direction. Your idea of acceleration
is an illusion of relative tire/road motion.

Most of the change of apparent linear speed comes from the effective
radius of the tyre increasing when the load of the car is removed. My
thick wall rigid runflats this would be about 1cm on 30cm radius tyres
~3% but on a conventional tyre underinflated it might be twice that.

When the tire suddenly inflates, and circumference increases, as the load
disappears, its moment of inertia will suddenly increase. If rpm is unchanged,
while the moment increases, there would be an increase in angular
momentum. I believe nature would frown on that -

The moment of inertia only increases by a tiny amount where the flat
part moves back out to full unloaded radius (roughly proportional to the
change in shape - which covers a very small part of the circumference).
It does slightly increase the moment of inertia but not by much.

Both effects (circumference and moment) are small, but angular velocity
must slightly diminish.

The angular velocity will slightly diminish but the change in effective
rolling diameter is sufficiently large that it wins hands down. The
linear speed of the tyre will increase to match the new diameter subject
and its rotation rate will slow to the constraint of conservation of
energy. The resulting equilibrium is the tyre after escape moves a bit
faster than the truck it fell off.

You wish to argue that the moment will increase, the rpm will drop
(to preserve angular momentum), and linear speed will increase, due
to larger circumference.

Possibly... or maybe impossible. Sounds contradictory to me.
The moment goes as the integral of r², whereas the circumference
of an \'effective circle\' is proportional to r.

There\'s probably a theorem in here somewhere - call the Theoretical
Physicist Hotline -


PS it\'s spelled \'tire\' - upgrade your spell checker -

--
Rich

 

[Jasen Betts]

On 2023-04-24, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

mandag den 24. april 2023 kl. 20.12.14 UTC+2 skrev John Larkin:
On Mon, 24 Apr 2023 09:24:51 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

mandag den 24. april 2023 kl. 00.33.17 UTC+2 skrev John Larkin:
On Sun, 23 Apr 2023 15:19:40 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Sunday, April 23, 2023 at 1:03:04?PM UTC-4, John Robertson wrote:
On 2023/04/23 4:01 a.m., Fred Bloggs wrote:
So a vehicle is driving down the road when an entire wheel comes off and continues its direction unchanged rolling alongside the vehicle. Question is why does the wheel end up accelerating, rolling much faster than its original speed, outpacing the vehicle significantly? Answer should be obvious, but you need practical insight.
The wheel can\'t accelerate without an external force being added to it -
it has no means of self propulsion. Laws of the conservation of momentum
apply as usual.

Think of a figure skater doing one of those stationary spins. Arms outstretched is one spin rate, arms brought into the side and they turn into a blur. No external forces come into play.

The skater must use muscle power to pull her arms in. The work done in
pulling her arms in is converted to energy stored in the spinning mass
of her body, and is recoverable.

angular momentum is the product of moment of inertia and angular velocity

angular momentum can\'t just change (newtons 3rd) so when the moment of inertia get smaller (pulling arms in)
the angular velocity has to increase

no energy added, just \"stored\" differently
She did work pulling her arms in, burned a bit of breakfast and added
energy to the rotating system.

sure she spend some energy but it doesn\'t add to the rotational energy

Didn\'t add rotational momentum, but did add rotational kinetic energy.

--
Jasen.
🇺🇦 Слава Україні

 

[Fred Bloggs]

On Friday, April 28, 2023 at 8:00:48 PM UTC-4, Jasen Betts wrote:

On 2023-04-24, Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
mandag den 24. april 2023 kl. 20.12.14 UTC+2 skrev John Larkin:
On Mon, 24 Apr 2023 09:24:51 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

mandag den 24. april 2023 kl. 00.33.17 UTC+2 skrev John Larkin:
On Sun, 23 Apr 2023 15:19:40 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Sunday, April 23, 2023 at 1:03:04?PM UTC-4, John Robertson wrote:
On 2023/04/23 4:01 a.m., Fred Bloggs wrote:
So a vehicle is driving down the road when an entire wheel comes off and continues its direction unchanged rolling alongside the vehicle. Question is why does the wheel end up accelerating, rolling much faster than its original speed, outpacing the vehicle significantly? Answer should be obvious, but you need practical insight.
The wheel can\'t accelerate without an external force being added to it -
it has no means of self propulsion. Laws of the conservation of momentum
apply as usual.

Think of a figure skater doing one of those stationary spins. Arms outstretched is one spin rate, arms brought into the side and they turn into a blur. No external forces come into play.

The skater must use muscle power to pull her arms in. The work done in
pulling her arms in is converted to energy stored in the spinning mass
of her body, and is recoverable.

angular momentum is the product of moment of inertia and angular velocity

angular momentum can\'t just change (newtons 3rd) so when the moment of inertia get smaller (pulling arms in)
the angular velocity has to increase

no energy added, just \"stored\" differently
She did work pulling her arms in, burned a bit of breakfast and added
energy to the rotating system.

sure she spend some energy but it doesn\'t add to the rotational energy

Didn\'t add rotational momentum, but did add rotational kinetic energy.

Angular kinetic energy is 1/2 I w^2, obvious notation, I moment of inertia about axis of rotation. Bringing the arms in reduces I forcing w to increase to maintain the same energy, which is ideally conserved.

--
Jasen.
🇺🇦 Слава Україні