Looking for a sanity check. If the washing m/c spins at 1400 rpm and has a drum radius of 25 cm. my dozy calculation is that the centrifugal force is around 672g.

Just sounds a little high.

rusty

therustyone wrote:

Looking for a sanity check. If the washing m/c spins at 1400 rpm and
has a drum radius of 25 cm. my dozy calculation is that the
centrifugal force is around 672g.

Just sounds a little high.

But only a little, I make it

((2Ï€ * rpm/60)^2 * r)

((2Ï€ * 23.33)^2 * 0.25)/9.81 = 547g

On 07/08/2016 11:21, therustyone wrote:
Looking for a sanity check. If the washing m/c spins at 1400 rpm and
has a drum radius of 25 cm. my dozy calculation is that the
centrifugal force is around 672g.

Just sounds a little high.

w = 1400 * 2 * pi / 60 = 146 rad/s

r = 0.25

F = m x w^2 x r

given g is 9.81, I make the force 550g, same league as your calculation.

Have I gone wrong as well?

On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone
wrote:

Looking for a sanity check. If the washing m/c spins at 1400 rpm and has a drum radius of 25 cm. my dozy calculation is that the centrifugal force is around 672g.

Just sounds a little high.

rusty

Well, according to this http://tinyurl.com/7cnp8h2 it is, but only a
little. That link gives a figure of 547.94g for the centrifugal
acceleration, assuming a radius of 0.25m and 1400 rpm.

To know the force, you also need to know the mass that you're hurling
around. A mass of 10kg requires a centrifugal force of 5479.4
kg-force.

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is used
to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was fictitious.

On Sun, 07 Aug 2016 11:55:53 +0100, Chris Hogg wrote:

Of course, as it points out in that link, centrifugal force is
fictitious.

Er, no. In fact if you spin a flywheel up to the point where it shatters,
that failure is a direct result of the opposition of centrifugal and
centripetal forces within it.

On Sun, 07 Aug 2016 11:53:28 +0100, Fredxxx wrote:

Have I gone wrong as well?

I very much doubt it. When it comes to calculations, you're the TOP DOG
here.

On 07/08/2016 12:46, Cursitor Doom wrote:
On Sun, 07 Aug 2016 11:53:28 +0100, Fredxxx wrote:

Have I gone wrong as well?

I very much doubt it. When it comes to calculations, you're the TOP DOG
here.

One of the secrets of any calculation is to have a feel for the result.
I thought the result was too high hence my concern.

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

On 07/08/16 12:30, Fredxxx wrote:
On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone

[...]

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is used
to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was fictitious.


Yes, the technically minded often have a woeful understanding of
language. There is nothing fictitious about centrifugal force, it is
knackering the main bearing of my washing machine even as I type
(terrible noise coming from back corridor). It is just a misnomer.

Tim W

On Sunday, 7 August 2016 12:51:50 UTC+1, Fredxxx wrote:
On 07/08/2016 12:46, Cursitor Doom wrote:
On Sun, 07 Aug 2016 11:53:28 +0100, Fredxxx wrote:

One of the secrets of any calculation is to have a feel for the result.
I thought the result was too high hence my concern.

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

The forces on those bearings are huge. What I was always more wary of though were the large top loaders. With far more weight & diameter, and lots of rust etc, being near those when they got upto a roaring spin was a reminder of one's nonrobustness in this life.


NT

On 07/08/16 12:56, TimW wrote:
On 07/08/16 12:30, Fredxxx wrote:
On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone

[...]

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is used
to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was fictitious.


Yes, the technically minded often have a woeful understanding of
language. There is nothing fictitious about centrifugal force, it is
knackering the main bearing of my washing machine even as I type
(terrible noise coming from back corridor). It is just a misnomer.

Centrifugal force is as fictitious as the earth going round the sun,
when everybody knows they are merely following the line of least
resistance through curved spacetime.

Tim W


--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

"TimW" wrote in message ...

On 07/08/16 12:30, Fredxxx wrote:
On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone

[...]

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is used
to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was fictitious.


Yes, the technically minded often have a woeful understanding of language.
There is nothing fictitious about centrifugal force, it is knackering the
main bearing of my washing machine even as I type (terrible noise coming
from back corridor). It is just a misnomer.

Vocabulary - corridor, passage. Be thankful.

On Sun, 7 Aug 2016 12:51:47 +0100, Fredxxx wrote:

snip

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

When we salvaged a 13 month old, written off as (financially)
irreparable Zanussi washing machine because of shot bearings (and made
it run another 7 years), the max spin rpm was 1400 but on the plastic
tub it was clearly marked 'Max 1100 RPM'.

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

Cheers, T i m

Dunno, could be more than that depending on how wet the stuff inside is I
suppose. My machine does not spin at full rate until the clothes get a lot
drier so obviously there has to be some monitoring going on or the poor
thing would shake itself to bits.

Anyway, I had a science teacher who maintained that we should in fact call
it centripetal force.


Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
"therustyone" wrote in message
...
Looking for a sanity check. If the washing m/c spins at 1400 rpm and has
a drum radius of 25 cm. my dozy calculation is that the centrifugal force
is around 672g.

Just sounds a little high.

rusty

On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads. These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

Brian-Gaff wrote:

I had a science teacher who maintained that we should in fact call
it centripetal force.

Didn't we all?

On 07/08/2016 13:45, Andy Burns wrote:
Brian-Gaff wrote:

I had a science teacher who maintained that we should in fact call
it centripetal force.

Didn't we all?

If you look at wikipedia definitions centripetal force is the force
exerted outwards through rotation, and centrifugal force is that
opposing it.

Common usage ignores the sign of the force, and mixes the two up. YMMV
which term you use although centrifugal is the more common used word and
perhaps the most understood.

Fredxxx wrote:

Andy Burns wrote:

Brian-Gaff wrote:

I had a science teacher who maintained that we should in fact call
it centripetal force.

Didn't we all?

If you look at wikipedia definitions centripetal force is the force
exerted outwards through rotation, and centrifugal force is that
opposing it.

Hence we were told to think of it as *negative* centripetal force, the
text books all called it centrifugal force though, and I think the
physics master knew that, for most of us, it was enough that we knew
both names.

On 07/08/16 13:28, Richard wrote:
"TimW" wrote in message ...

On 07/08/16 12:30, Fredxxx wrote:
[...]

even as I type
(terrible noise coming from back corridor). It is just a misnomer.

Vocabulary - corridor, passage. Be thankful.

lol!

On Sun, 7 Aug 2016 12:38:05 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads.

True, but aren't they managed / limited on most machines and then
only really impacting when trying to rotate them at speed?

These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

True, I don't know how well they have to be distributed other than
I've seen our machine having several 'goes' at re-distributing
(randomly of course) the clothes to try to get something acceptable.

So, IMHO, a clump of clothes being thrown about when in the std
washing cycle wouldn't be too much of an issue. Trying to minimise the
clumps (and the weight of the water they may contain) whilst going for
a high speed spin is / causes harder work.

If you look at the g-force calculations seen elsewhere in this thread
it's proportional to speed and when in the washing cycle that speed is
very very low.

10kg of load in the drum is only going to put 10kg worth of 'load' on
the bearings. As you say, even 1kg's worth of imbalance is going to
weigh a lot more than that at 1400 rpm! ;-(

Cheers, T i m

On 07/08/2016 15:13, T i m wrote:
On Sun, 7 Aug 2016 12:38:05 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads.

True, but aren't they managed / limited on most machines and then
only really impacting when trying to rotate them at speed?

These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

True, I don't know how well they have to be distributed other than
I've seen our machine having several 'goes' at re-distributing
(randomly of course) the clothes to try to get something acceptable.

So, IMHO, a clump of clothes being thrown about when in the std
washing cycle wouldn't be too much of an issue. Trying to minimise the
clumps (and the weight of the water they may contain) whilst going for
a high speed spin is / causes harder work.

If you look at the g-force calculations seen elsewhere in this thread
it's proportional to speed.

No its a square function of "speed" 2 x speed = 4 x the force.

On Sunday, 7 August 2016 13:32:56 UTC+1, T i m wrote:
On Sun, 7 Aug 2016 12:51:47 +0100, Fredxxx wrote:

snip

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

When we salvaged a 13 month old, written off as (financially)
irreparable Zanussi washing machine because of shot bearings (and made
it run another 7 years), the max spin rpm was 1400 but on the plastic
tub it was clearly marked 'Max 1100 RPM'.

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

Cheers, T i m

High spin speed seems to be more a selling point than anything else. It isn't necessary and shortens bearing life greatly.

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.


NT

On Sunday, 7 August 2016 13:32:56 UTC+1, T i m wrote:
On Sun, 7 Aug 2016 12:51:47 +0100, Fredxxx wrote:

snip

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

When we salvaged a 13 month old, written off as (financially)
irreparable Zanussi washing machine because of shot bearings (and made
it run another 7 years), the max spin rpm was 1400 but on the plastic
tub it was clearly marked 'Max 1100 RPM'.

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

Cheers, T i m

What ****s up main bearings is the failure of the water seal which results in washing out the grease resulting in bearing failure.
I only ever once saw a drum "burst".
(I used to repair washing machines)
A long time ago.

On Sunday, 7 August 2016 15:13:03 UTC+1, T i m wrote:
On Sun, 7 Aug 2016 12:38:05 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads.

True, but aren't they managed / limited on most machines and then
only really impacting when trying to rotate them at speed?

These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

True, I don't know how well they have to be distributed other than
I've seen our machine having several 'goes' at re-distributing
(randomly of course) the clothes to try to get something acceptable.

So, IMHO, a clump of clothes being thrown about when in the std
washing cycle wouldn't be too much of an issue. Trying to minimise the
clumps (and the weight of the water they may contain) whilst going for
a high speed spin is / causes harder work.

If you look at the g-force calculations seen elsewhere in this thread
it's proportional to speed and when in the washing cycle that speed is
very very low.

10kg of load in the drum is only going to put 10kg worth of 'load' on
the bearings. As you say, even 1kg's worth of imbalance is going to
weigh a lot more than that at 1400 rpm! ;-(

Cheers, T i m

Before spinning, washing machine run at an intermediate speed that is supposed to distribute the washing around the drum.

On Sunday, 7 August 2016 16:04:32 UTC+1, wrote:
On Sunday, 7 August 2016 13:32:56 UTC+1, T i m wrote:
On Sun, 7 Aug 2016 12:51:47 +0100, Fredxxx wrote:

snip

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

When we salvaged a 13 month old, written off as (financially)
irreparable Zanussi washing machine because of shot bearings (and made
it run another 7 years), the max spin rpm was 1400 but on the plastic
tub it was clearly marked 'Max 1100 RPM'.

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

Cheers, T i m

High spin speed seems to be more a selling point than anything else. It isn't necessary and shortens bearing life greatly.

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.


NT

Sin speeds are higher because you can have a smaller washing machine.

On Sunday, 7 August 2016 16:12:06 UTC+1, harry wrote:
On Sunday, 7 August 2016 16:04:32 UTC+1, tabbypurr wrote:

High spin speed seems to be more a selling point than anything else. It isn't necessary and shortens bearing life greatly.

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.

Sin speeds are higher because you can have a smaller washing machine.

Machine size is governed by load capacity, not spin speed. What spin speed you get is just extras.


NT

On 07/08/2016 16:24, wrote:
On Sunday, 7 August 2016 16:12:06 UTC+1, harry wrote:
On Sunday, 7 August 2016 16:04:32 UTC+1, tabbypurr wrote:

High spin speed seems to be more a selling point than anything
else. It isn't necessary and shortens bearing life greatly.

I don't remember what early front loaders did, if 600 or 800 it
would have been more significant then.

Sin speeds are higher because you can have a smaller washing
machine.

Machine size is governed by load capacity, not spin speed. What spin
speed you get is just extras.

Big machines have lower spin speeds?

On Sun, 7 Aug 2016 15:59:52 +0100, Fredxxx wrote:

On 07/08/2016 15:13, T i m wrote:
On Sun, 7 Aug 2016 12:38:05 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads.

True, but aren't they managed / limited on most machines and then
only really impacting when trying to rotate them at speed?

These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

True, I don't know how well they have to be distributed other than
I've seen our machine having several 'goes' at re-distributing
(randomly of course) the clothes to try to get something acceptable.

So, IMHO, a clump of clothes being thrown about when in the std
washing cycle wouldn't be too much of an issue. Trying to minimise the
clumps (and the weight of the water they may contain) whilst going for
a high speed spin is / causes harder work.

If you look at the g-force calculations seen elsewhere in this thread
it's proportional to speed.

No its a square function of "speed" 2 x speed = 4 x the force.

Sorry, I didn't mean it was linear, I meant it changes as a function
of the speed to some proportion (as you say, squared)? ;-)

Cheers, T i m

On Sun, 7 Aug 2016 08:04:28 -0700 (PDT), wrote:

snip

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

snip

High spin speed seems to be more a selling point than anything else.

Agreed, it 'probably' is.

It isn't necessary

It would be interesting to see if anyone has done a water content
(weight) test on a known quantity of material and at the complete
range of speeds?

and shortens bearing life greatly.

So it seems. ;-(

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.

That sounds about right .. and like many things those sorts of speeds
may have been easily doable by the most basic of materials (like
bearings). I know Mums old Hotpoint must be 20+ years old now (I can't
remember ever changing the bearings and it would have been me if
anyone) and probably has a fairly low spin speed.

Cheers, T i m

On Sun, 7 Aug 2016 08:06:34 -0700 (PDT), harry
wrote:

snip

Maybe part of getting more than 7 times the life out of it post
salvage than from the factory was as you suggest, the fact that we
used a max 900 RPM spin speed? (Given that is was still 200 RPM better
than the machine it replaced).

snip

What ****s up main bearings is the failure of the water seal which results in washing out the grease resulting in bearing failure.

When I split the unsplittable tub on this Zanussi and replaced the
(sealed) bearings I replaced the main seal and removed the seals on
the bearings that faced each other. I also replaced the grease with a
waterproof grease and drilled a small hole though the bearing housing
at about the half way mark to allow any water that did get in there to
drain. I wanted to take the thing to bits to see exactly what had
happened but we had washing needing doing and daughter replaced the
machine for us (both physically and financially). ;-)

I only ever once saw a drum "burst".

I've never seen one but heard of one doing so here.

(I used to repair washing machines)
A long time ago.

Wasn't there a safety issue with the belt coming down from the
overhead drive shaft? ;-)

Cheers, T i m

In article ,
Cursitor Doom writes:
On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads. These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

My (1987-ish) Hotpoint 1400 RPM microprocessor controlled
machine would have at to 3 goes at distributing the load, after
which it would spin at only 1000 RPM if unsuccessful.

Distributing the load was done by slowly cranking up the
rotation speed until it got to over 1g force so clothes stopped
tumbling and stuck to drum, and checking for constant rotation
speed (i.e. not speeding up and slowing down as a clump of clothes
is lifted and dropped each revolution). This worked reasonably well
except it couldn't detect off-balance load front-to-back (i.e. half
the weight one side at the front, other half other side at the back).
This also requires a tachometer (which this machine had) so it can
detect speed changes within one drum revolution (which was done by
mounting it on the back of the motor, which spins much faster than
the drum).

Some other makes used a pedulum detector on the drum for off-balance
loads, but those tended to cut the spinning at that point, rather than
trying to avoid the off-balance load in the first place.

A colleague bought a slightly earlier model whem max spin speed was
1300 RPM. The first time it spun, the concrete weights on the drum
turned into a pile of grit on the floor under the machine!
Apparently, a duff batch of concrete was used for a set of weights.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 07/08/2016 16:29, Fredxxx wrote:
On 07/08/2016 16:24, wrote:
On Sunday, 7 August 2016 16:12:06 UTC+1, harry wrote:
On Sunday, 7 August 2016 16:04:32 UTC+1, tabbypurr wrote:

High spin speed seems to be more a selling point than anything
else. It isn't necessary and shortens bearing life greatly.

I don't remember what early front loaders did, if 600 or 800 it
would have been more significant then.

Sin speeds are higher because you can have a smaller washing
machine.

Machine size is governed by load capacity, not spin speed. What spin
speed you get is just extras.

Big machines have lower spin speeds?

The makers claim various spin speeds as rpm - and never refer to the
varying diameters of the drums. A big machine (large diameter) could
have a lower spin speed (rpm) but a better drying performance.

--
Rod

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

not an option (on a Siemens). I do have a 5 year guarantee.

On Sunday, August 7, 2016 at 11:44:18 AM UTC+1, Andy Burns wrote:
therustyone wrote:

Looking for a sanity check. If the washing m/c spins at 1400 rpm and
has a drum radius of 25 cm. my dozy calculation is that the
centrifugal force is around 672g.

Just sounds a little high.

But only a little, I make it

((2Ï€ * rpm/60)^2 * r)

((2Ï€ * 23.33)^2 * 0.25)/9.81 = 547g

thanks for that. I'm not a mad as I thought I was.

The point is though it is really the effect that occurs when things moving
in a single direction are forced to deviate from that path in a circle.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Andy Burns" wrote in message
...
Fredxxx wrote:

Andy Burns wrote:

Brian-Gaff wrote:

I had a science teacher who maintained that we should in fact call
it centripetal force.

Didn't we all?

If you look at wikipedia definitions centripetal force is the force
exerted outwards through rotation, and centrifugal force is that
opposing it.

Hence we were told to think of it as *negative* centripetal force, the
text books all called it centrifugal force though, and I think the physics
master knew that, for most of us, it was enough that we knew both names.

On 07/08/2016 20:42, Brian Gaff wrote:
The point is though it is really the effect that occurs when things moving
in a single direction are forced to deviate from that path in a circle.
Brian


One of the issues with the term centrifugal is the apparent, albeit
simplistic, inference that things would literally fly out from the
centre - rather than continue on their tangential path - if released.

--
Rod

"polygonum" wrote in message
...
On 07/08/2016 20:42, Brian Gaff wrote:
The point is though it is really the effect that occurs when things
moving
in a single direction are forced to deviate from that path in a circle.
Brian


One of the issues with the term centrifugal is the apparent, albeit
simplistic, inference that things would literally fly out from the
centre - rather than continue on their tangential path - if released.

If you take a cotton reel and thread a piece of string through it, and
attach a light weight on one end and a heavy weight of the other end, and
then spin the light weight around your head by holding onto the cotton reel,
the light weight will lift up the heavy weight once you spin it fast enough.

This happens once m(light) x r x angular speed = m(heavy) * g. But the
direction of the force is clearly acting *away* from the centre; if it was
acting towards the centre the heavy weight would fall, not rise, as the
speed increased.

My physics teacher could never explain this. We gave him a hard time about
it - that and also because his name was J R Hartley, at the time of the
"Fly-Fishing by J R Hartley" Yellow Pages adverts on TV :-)

On 8/7/2016 12:59 PM, wrote:
On Sunday, 7 August 2016 12:51:50 UTC+1, Fredxxx wrote:
On 07/08/2016 12:46, Cursitor Doom wrote:
On Sun, 07 Aug 2016 11:53:28 +0100, Fredxxx wrote:

One of the secrets of any calculation is to have a feel for the result.
I thought the result was too high hence my concern.

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

The forces on those bearings are huge. What I was always more wary of though were the large top loaders. With far more weight & diameter, and lots of rust etc, being near those when they got upto a roaring spin was a reminder of one's nonrobustness in this life.


NT


Rolling element bearings will take amazingly high loads. Part of the
skill in designing washing machines is in the suspension (stiffness,
range, damping). Obviously, you can never get perfect balance so the
drum axis moves in small circles around the centre of mass, this means
the loads on the bearings are much lower than you might expect from the
calc which you have done.

On 8/7/2016 4:59 PM, Andrew Gabriel wrote:
In article ,
Cursitor Doom writes:
On Sun, 07 Aug 2016 13:32:55 +0100, T i m wrote:

I'm pretty sure it's only the spin cycle that puts a real strain on
anything?

I'd venture to say that "real strain" on the system comes from unbalanced
loads. These things would last a hell of a lot longer if the load were
evenly distributed (which of course it invariably isn't).

My (1987-ish) Hotpoint 1400 RPM microprocessor controlled
machine would have at to 3 goes at distributing the load, after
which it would spin at only 1000 RPM if unsuccessful.

Distributing the load was done by slowly cranking up the
rotation speed until it got to over 1g force so clothes stopped
tumbling and stuck to drum, and checking for constant rotation
speed (i.e. not speeding up and slowing down as a clump of clothes
is lifted and dropped each revolution). This worked reasonably well
except it couldn't detect off-balance load front-to-back (i.e. half
the weight one side at the front, other half other side at the back).
This also requires a tachometer (which this machine had) so it can
detect speed changes within one drum revolution (which was done by
mounting it on the back of the motor, which spins much faster than
the drum).

Some other makes used a pedulum detector on the drum for off-balance
loads, but those tended to cut the spinning at that point, rather than
trying to avoid the off-balance load in the first place.


Interesting!

On 8/7/2016 1:28 PM, Richard wrote:
"TimW" wrote in message ...

On 07/08/16 12:30, Fredxxx wrote:
On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone

[...]

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is used
to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was
fictitious.


Yes, the technically minded often have a woeful understanding of
language. There is nothing fictitious about centrifugal force, it is
knackering the main bearing of my washing machine even as I type
(terrible noise coming from back corridor). It is just a misnomer.

Vocabulary - corridor, passage. Be thankful.

It's when the seals fail that they die. Water in the bearings wrecks the
lubrication, and puts the fatigue rates up by one or two orders of
magnitude.

On 07/08/16 21:20, NY wrote:
"polygonum" wrote in message
...
On 07/08/2016 20:42, Brian Gaff wrote:
The point is though it is really the effect that occurs when things
moving
in a single direction are forced to deviate from that path in a circle.
Brian


One of the issues with the term centrifugal is the apparent, albeit
simplistic, inference that things would literally fly out from the
centre - rather than continue on their tangential path - if released.

If you take a cotton reel and thread a piece of string through it, and
attach a light weight on one end and a heavy weight of the other end,
and then spin the light weight around your head by holding onto the
cotton reel, the light weight will lift up the heavy weight once you
spin it fast enough.

This happens once m(light) x r x angular speed = m(heavy) * g. But the
direction of the force is clearly acting *away* from the centre; if it
was acting towards the centre the heavy weight would fall, not rise, as
the speed increased.

My physics teacher could never explain this. We gave him a hard time
about it - that and also because his name was J R Hartley, at the time
of the "Fly-Fishing by J R Hartley" Yellow Pages adverts on TV :-)

Maybe I can:

The force (tension) in the string provided by the heavy weight
*provides* the centripetal force required to maintain the light weight
in its orbit.



As Newton said every action has an equal and opposite reaction, you
could equally claim the the light weight is providing lift to the heavy
weight. In one sense this is perfectly correct. The only problem comes,
as said by others, that if the string breaks, the light weight continues
on its path - it does not fly in the radial direction of the string.



Obviously at some point the system may be unbalanced - in which case the
heavy weight will rise or fall, adjusting the radius of orbit of the
light weight until the system balances or the string hits one of its limits.