Physics Quiz...

[Anthony William Sloman]

On Sunday, April 23, 2023 at 11:53:35 PM UTC+10, Tabby wrote:

On Sunday, 23 April 2023 at 12:49:24 UTC+1, 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.
a hill, obviously

It could, but it isn\'t implied by the form of the question. \"Driving down the road\" isn\'t \"driving down a hill\", and the question wouldn\'t be worthy posing if the car was driving down a hill. This doesn\'t stop Tabby from trying for a cheap shot.

--
Bill Sloman, Sydney

 

[John Robertson]

On 2023/04/23 11:41 a.m., John Larkin wrote:

On Sun, 23 Apr 2023 10:02:54 -0700, John Robertson <jrr@flippers.com
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.


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

Yes, there is stored energy in the tire, if said tire is under traction
or compression - which preloads the tread, the moment it is released.
Its velocity has an almost instantaneous increase - like a coiled spring
that has been released.

There is no energy input though. So no additional acceleration once the
tire has separated from the axle.

At which point the energy stored in the rotating tire is dissipated
through friction and it starts to slow down. Not as fast as the vehicle
will though! Which leads one to think the tire is accelerating, rather
than the vehicle is decelerating. It depends on your perspective. One
(an outside observer) conserves the law of momentum, the other (viewed
from inside the vehicle) appears to break it.

John :-#)#

 

[Clive Arthur]

On 23/04/2023 12:01, 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.

It\'s a bit like one of those old jokes. The physicist starts talking
about conservation of angular momentum, the engineer says the wheel just
got bigger, and the mathematician says, \"consider a spherical wheel with
unit radius...\"

--
Cheers
Clive

 

[John Walliker]

On Sunday, 23 April 2023 at 23:17:50 UTC+1, 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. But it doesn\'t explain the increase in rotational speed.

There\'s a second element hit on by JL, and that is the ability of tire to store energy in its elasticity. These runaway tires almost always break into a bounce, they can bounce really high, and then they really start flying..

BTW Wheels shouldn\'t drop off properly maintained vehicles.

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.

That happened to the car in front of my wife once on a motorway. A wheel dropped off a vehicle on
the other side of the motorway, bounced across the central barrier and landed
on the windscreen of the car in front of her. The driver managed to stop under control and
did not appear to be seriously injured, which is remarkable as the relative velocity
of the wheel and car was around 150mph.
John

 

[Martin Brown]

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.

It is possible that the stored energy in the wheel will tend to spin it
up because AOTBE the last point of contact will be the front edge of the
wheel where it was previously being deformed (until it clears the ground).

There\'s a second element hit on by JL, and that is the ability of
tire to store energy in its elasticity. These runaway tires almost
always break into a bounce, they can bounce really high, and then
they really start flying.

You talk as if these are common occurrences. I have never witnessed it
once in many decades of driving.

I have lost count of the number of times I have seen people driving on
flat tyres (up to the point where they catch fire or ruin a wheel).

BTW Wheels shouldn\'t drop off properly maintained vehicles.

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?

--
Martin Brown

 

[John Larkin]

On Mon, 24 Apr 2023 10:24:00 +0100, Martin Brown
<\'\'\'newspam\'\'\'@nonad.co.uk> 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.

It is possible that the stored energy in the wheel will tend to spin it
up because AOTBE the last point of contact will be the front edge of the
wheel where it was previously being deformed (until it clears the ground).

There\'s a second element hit on by JL, and that is the ability of
tire to store energy in its elasticity. These runaway tires almost
always break into a bounce, they can bounce really high, and then
they really start flying.

You talk as if these are common occurrences. I have never witnessed it
once in many decades of driving.

I have lost count of the number of times I have seen people driving on
flat tyres (up to the point where they catch fire or ruin a wheel).

BTW Wheels shouldn\'t drop off properly maintained vehicles.

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?

It is a big country.

Looks like mostly truck tires to me.

https://www.youtube.com/watch?v=Nk4OzPLvxuE

https://www.youtube.com/watch?v=swSLMDLHrKQ

They don\'t seem to accelerate after they break off.

 

[Anthony William Sloman]

On Monday, April 24, 2023 at 6:49:08 PM UTC+10, Clive Arthur wrote:

On 23/04/2023 12:01, 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.
It\'s a bit like one of those old jokes. The physicist starts talking
about conservation of angular momentum, the engineer says the wheel just
got bigger, and the mathematician says, \"consider a spherical wheel with
unit radius...\"

A mathematician would go for toroidal wheel. Admittedly it has two radii but at least it looks like a wheel.

--
Bill Sloman, Sydney

 

[Lasse Langwadt Christensen]

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

 

[boB]

On Mon, 24 Apr 2023 07:50:03 -0700 (PDT), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

On Monday, April 24, 2023 at 6:49:08?PM UTC+10, Clive Arthur wrote:
On 23/04/2023 12:01, 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.
It\'s a bit like one of those old jokes. The physicist starts talking
about conservation of angular momentum, the engineer says the wheel just
got bigger, and the mathematician says, \"consider a spherical wheel with
unit radius...\"

A mathematician would go for toroidal wheel. Admittedly it has two radii but at least it looks like a wheel.

My guess is that, mainly, the car slowed down cuz it was missing a
wheel.

Without an absolute measurement of velocity of the car and of the free
rolling wheel in reference to the ground, who knows /

boB

 

[Ralph Mowery]

In article <o9bd4idr642oadqj1e76os1a60va2r9ass@4ax.com>, boB@K7IQ.com
says...

My guess is that, mainly, the car slowed down cuz it was missing a
wheel.

Without an absolute measurement of velocity of the car and of the free
rolling wheel in reference to the ground, who knows /

The car I was in when the wheel came off was doing a constant speed as
the wheel passed us.

 

[Fred Bloggs]

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.

It is possible that the stored energy in the wheel will tend to spin it
up because AOTBE the last point of contact will be the front edge of the
wheel where it was previously being deformed (until it clears the ground)..

There\'s a second element hit on by JL, and that is the ability of
tire to store energy in its elasticity. These runaway tires almost
always break into a bounce, they can bounce really high, and then
they really start flying.
You talk as if these are common occurrences. I have never witnessed it
once in many decades of driving.

I have lost count of the number of times I have seen people driving on
flat tyres (up to the point where they catch fire or ruin a wheel).
BTW Wheels shouldn\'t drop off properly maintained vehicles.

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....

--
Martin Brown

 

[Fred Bloggs]

On Monday, April 24, 2023 at 12:26:22 PM UTC-4, boB wrote:

On Mon, 24 Apr 2023 07:50:03 -0700 (PDT), Anthony William Sloman
bill....@ieee.org> wrote:
On Monday, April 24, 2023 at 6:49:08?PM UTC+10, Clive Arthur wrote:
On 23/04/2023 12:01, 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.
It\'s a bit like one of those old jokes. The physicist starts talking
about conservation of angular momentum, the engineer says the wheel just
got bigger, and the mathematician says, \"consider a spherical wheel with
unit radius...\"

A mathematician would go for toroidal wheel. Admittedly it has two radii but at least it looks like a wheel.
My guess is that, mainly, the car slowed down cuz it was missing a
wheel.

The wheel will catch the cars in front of the car that lost it, and they did not slow down. That wheel definitely accelerates when it\'s on its own.

Without an absolute measurement of velocity of the car and of the free
rolling wheel in reference to the ground, who knows /

boB

 

[Fred Bloggs]

On Sunday, April 23, 2023 at 6:48:05 PM UTC-4, 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.

It\'s too complex to analyze.

You might be on to something there. The nature of the failure somehow gives the wheel a push before it breaks free.

 

[John Larkin]

On Mon, 24 Apr 2023 09:24:51 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@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. When she extends them back out, work is
done on her arms. Of course, muscles don\'t recover energy when
back-driven but some other gadget, a prosthetic arm maybe, could.

One could build a robot lady to do the skater spin thing. If it could
recover the energy supplied when it extends its arms, it could spin up
and down forever without needing additional power.

Energy is conserved.

 

[Lasse Langwadt Christensen]

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

 

[John Larkin]

On Mon, 24 Apr 2023 12:49:28 -0700 (PDT), 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

Energy is conserved. The work she does to pull her arms in isn\'t lost,
and can be recovered. It can only be stored in the rotational energy.

 

[Lasse Langwadt Christensen]

mandag den 24. april 2023 kl. 22.07.22 UTC+2 skrev John Larkin:

On Mon, 24 Apr 2023 12:49:28 -0700 (PDT), 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



Energy is conserved. The work she does to pull her arms in isn\'t lost,
and can be recovered. It can only be stored in the rotational energy.

what if she is standing still?

 

[John Larkin]

On Mon, 24 Apr 2023 13:13:48 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

mandag den 24. april 2023 kl. 22.07.22 UTC+2 skrev John Larkin:
On Mon, 24 Apr 2023 12:49:28 -0700 (PDT), 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



Energy is conserved. The work she does to pull her arms in isn\'t lost,
and can be recovered. It can only be stored in the rotational energy.

what if she is standing still?

\"Think of a figure skater doing one of those stationary spins.\"
started this.

 

[Tabby]

On Monday, 24 April 2023 at 18:36:45 UTC+1, Fred Bloggs wrote:

On Monday, April 24, 2023 at 12:26:22 PM UTC-4, boB wrote:
On Mon, 24 Apr 2023 07:50:03 -0700 (PDT), Anthony William Sloman
bill....@ieee.org> wrote:
On Monday, April 24, 2023 at 6:49:08?PM UTC+10, Clive Arthur wrote:
On 23/04/2023 12:01, 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.
It\'s a bit like one of those old jokes. The physicist starts talking
about conservation of angular momentum, the engineer says the wheel just
got bigger, and the mathematician says, \"consider a spherical wheel with
unit radius...\"

A mathematician would go for toroidal wheel. Admittedly it has two radii but at least it looks like a wheel.
My guess is that, mainly, the car slowed down cuz it was missing a
wheel.

The wheel will catch the cars in front of the car that lost it, and they did not slow down. That wheel definitely accelerates when it\'s on its own.

The moment the wheel breaks free, the car loses its engine power to the road due to the diff. Thus in most cases the car necessarily slows down.

Cars are much taller than tyres, so wind resistance has more effect on the car than the tyre.
Also the tyre is spinning, thus the angular momentum reduces its deceleration wrt the car.
Thus I\'m not surprised the tyre often overtakes the car.
No doubt the driver\'s reaction (braking) and the reality that a lot of roads aren\'t level also plays into it. Even if slowman fails to work it out, physics still applies.

 

[Tabby]

On Monday, 24 April 2023 at 19:12:14 UTC+1, John Larkin wrote:

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. When she extends them back out, work is
done on her arms. Of course, muscles don\'t recover energy when
back-driven but some other gadget, a prosthetic arm maybe, could.

One could build a robot lady to do the skater spin thing. If it could
recover the energy supplied when it extends its arms, it could spin up
and down forever without needing additional power.

In a vacuum. On a gas bearing. Which requires an infinitely powerful pump

> Energy is conserved.