"There is no reverse on a motorcycle ..." was supposedly one of Shannon's favorite test sentences. http://languagelog.ldc.upenn.edu/myl/Shannon1950.pdf --rwg From: meekerdb <meekerdb@verizon.net> On 1/27/2014 1:22 AM, Joerg Arndt wrote:
Most certainly a kind of motor is used where the initial internal position (and possibly the initial current) determines the direction.
But I've noticed that mine seems to be completely consistent. It reverses every time.
A similar thing used to be (long ago) a problem with tractors when the motor was idling: it could start moving backward when put into move, potentially injuring/killing the people accompanying it (usually walking behind).
A two-stroke engine will also run backwards. Even though the ignition timing is poor for running backward it can get started that way by kicking back when starting. Once at the start of a motorcycle race I saw kid have his bike lurch backwards as everyone else leaped forward. A look of puzzlement came over his face as he tried easing out the clutch again and the bike started to back up. Then he threw down the bike as if it had betrayed him. Brent Meeker
Best, jj
* James Propp <jamespropp@gmail.com> [Jan 27. 2014 10:12]:
Why do microwave ovens alternate between rotating the food-carousel clockwise and rotating it counterclockwise (or, as the
Brits
would say, anticlockwise)?
Jim Propp
OK, so why are μwave ovens so damn noisy? Note to James Randi: Unworthy nonbeliever, if you want to learn the true power of homeopathy, try making Earl Grey tea in a sauerkraut jar.
The Honda Gold Wing motorcycle, both has reverse and absolutely needs it! Old four engined bombers, such as the B-17 (which did not have reverse pitch propellers) could creep backwards on a taxiway up by alternately holding the brake on one wheel (e.g. The right side) while while advancing the throttle on the outboard engine on the same side and then, next, doing the same things on the other side… etc,, causing the aircraft to slowly wiggle backwards. My puny, mini 4 door Nissan Leaf, is the fastest production car in the world… going backwards (97 MPH). While certainly not obvious, computers can be designed to work backwards just as well as forwards (but usually only after going forwards can they then go backwards… too bad for those wanting to factor large integers but handy for those wanting to not necessarily dissipate any energy when computing!) When I was a kid, old gasoline powered model airplane engines ran backwards as well as forwards, sometimes spontaneously switching in flight with disastrous consequences. But the best such things are the most microscopic laws of physics, where absolutely everything that happens forwards, can also happen backwards… that is, CPT backwards. Ed Fredkin From: Bill Gosper <billgosper@gmail.com<mailto:billgosper@gmail.com>> Reply-To: <billgosper@gmail.com<mailto:billgosper@gmail.com>> Date: Mon, 27 Jan 2014 11:20:24 -0800 To: <math-fun@mailman.xmission.com<mailto:math-fun@mailman.xmission.com>> Subject: [math-fun] Microwave ovens "There is no reverse on a motorcycle ..." was supposedly one of Shannon's favorite test sentences. http://languagelog.ldc.upenn.edu/myl/Shannon1950.pdf --rwg From: meekerdb <meekerdb@verizon.net<mailto:meekerdb@verizon.net>> On 1/27/2014 1:22 AM, Joerg Arndt wrote:
Most certainly a kind of motor is used where the initial internal position (and possibly the initial current) determines the direction.
But I've noticed that mine seems to be completely consistent. It reverses every time.
A similar thing used to be (long ago) a problem with tractors when the motor was idling: it could start moving backward when put into move, potentially injuring/killing the people accompanying it (usually walking behind).
A two-stroke engine will also run backwards. Even though the ignition timing is poor for running backward it can get started that way by kicking back when starting. Once at the start of a motorcycle race I saw kid have his bike lurch backwards as everyone else leaped forward. A look of puzzlement came over his face as he tried easing out the clutch again and the bike started to back up. Then he threw down the bike as if it had betrayed him. Brent Meeker
Best, jj
* James Propp <jamespropp@gmail.com<mailto:jamespropp@gmail.com>> [Jan 27. 2014 10:12]:
Why do microwave ovens alternate between rotating the food-carousel clockwise and rotating it counterclockwise (or, as the Brits would say, anticlockwise)?
Jim Propp
OK, so why are μwave ovens so damn noisy? Note to James Randi: Unworthy nonbeliever, if you want to learn the true power of homeopathy, try making Earl Grey tea in a sauerkraut jar. -- You received this message because you are subscribed to the Google Groups "mathfuneavesdroppers" group. To unsubscribe from this group and stop receiving emails from it, send an email to mathfuneavesdroppers+unsubscribe@googlegroups.com<mailto:mathfuneavesdroppers+unsubscribe@googlegroups.com>. For more options, visit https://groups.google.com/groups/opt_out.
* Bill Gosper <billgosper@gmail.com> [Jan 28. 2014 09:46]:
[...]
OK, so why are μwave ovens so damn noisy?
The efficiency of the magnetron is not really near 100 per cent, so there is a rather great amount of heat the microwave needs to get rid of. Strong-ish airstream through rather randomly shaped duct ==> noise. Wiki states 64 per cent efficiency.
[...]
Many of them are also noisy in their damn beep-beep-beeping, which cannot be shut off in any oven I've ever seen. Even worse are the ones that beep-beep-beep repeatedly if you don't open the oven door right away. As though it were some emergency. And while I'm ranting: often an oven has a ridiculously cryptic user interface that one has to solve before using. And why do their inside surfaces have to be so irregular, making cleaning difficult? --Dan On 2014-01-28, at 1:01 AM, Joerg Arndt wrote:
* Bill Gosper <billgosper@gmail.com> [Jan 28. 2014 09:46]:
[...]
OK, so why are μwave ovens so damn noisy?
No excuses for the user interfaces. For the inner surfaces, however, I’m pretty sure they are intended to randomize the distribution of reflected internal radiation, which would, with smooth surfaces, likely bounce in very predictable ways, leading to local hot spots and cold spots. On Jan 28, 2014, at 3:35 PM, Dan Asimov <dasimov@earthlink.net> wrote:
Many of them are also noisy in their damn beep-beep-beeping, which cannot be shut off in any oven I've ever seen. Even worse are the ones that beep-beep-beep repeatedly if you don't open the oven door right away. As though it were some emergency.
And while I'm ranting: often an oven has a ridiculously cryptic user interface that one has to solve before using.
And why do their inside surfaces have to be so irregular, making cleaning difficult?
--Dan
On 2014-01-28, at 1:01 AM, Joerg Arndt wrote:
* Bill Gosper <billgosper@gmail.com> [Jan 28. 2014 09:46]:
[...]
OK, so why are μwave ovens so damn noisy?
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
OK, just one question: Does the basic design of a microwave oven require that the interior have holes in it? Those holes make it inevitable that as time marches on the oven starts to stink. --Dan On 2014-01-28, at 12:43 PM, Tom Knight wrote:
No excuses for the user interfaces. For the inner surfaces, however, I’m pretty sure they are intended to randomize the distribution of reflected internal radiation, which would, with smooth surfaces, likely bounce in very predictable ways, leading to local hot spots and cold spots.
There has to be a hole for radiation from the magnetron. The perforated holes on the front glass are much smaller than a wavelength, and that wall looks essentially solid. That would be true for other holes (although the seams along the door, being long in one dimension, can leak radiation). I had a colleague at MIT that made lots of money selling “radiation detectors” for microwaves to gullible people who thought that this radiation might hurt them. On Jan 28, 2014, at 4:14 PM, Dan Asimov <dasimov@earthlink.net> wrote:
OK, just one question: Does the basic design of a microwave oven require that the interior have holes in it? Those holes make it inevitable that as time marches on the oven starts to stink.
--Dan
On 2014-01-28, at 12:43 PM, Tom Knight wrote:
No excuses for the user interfaces. For the inner surfaces, however, I’m pretty sure they are intended to randomize the distribution of reflected internal radiation, which would, with smooth surfaces, likely bounce in very predictable ways, leading to local hot spots and cold spots.
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
I worked for a while at the US Public Health Service Northeastern Radiological Lab outside of Boston in late 1969. One of their tasks was to evaluate the safety of the then-novel microwave ovens, which were (at the time) too expensive for most households, but were quickly catching on in restaurants. We performed a survey of Boston-area restaurants, nightclubs and strip bars (!!) to check on the radiation leaking from the microwave ovens in use. I don't recall the percentage, but a small percentage of these ovens leaked enough radiation around the door seals to have to be shut down, as they could have caused eye cateracts in the kitchen workers near the oven. Much of the leakage was due to food buildup on the edges of the door, so poor door design was indicated. I think that most of these design defects were repaired in the 2nd or 3rd generation ovens, and I haven't heard of any further problems. However, in the early 1970's, there was a non-zero risk from microwaves escaping, so your colleague wasn't completely off base, at least in that time frame. Now the real question is how to hook up your microwave oven to your wifi, so you can communicate with the Space Shuttle. ;-) (High gain antennas for wifi's are already used by ham radio operators to communicate over 10's of miles, line of sight.) At 01:26 PM 1/28/2014, Tom Knight wrote:
There has to be a hole for radiation from the magnetron. The perforated holes on the front glass are much smaller than a wavelength, and that wall looks essentially solid. That would be true for other holes (although the seams along the door, being long in one dimension, can leak radiation). I had a colleague at MIT that made lots of money selling radiation detectors for microwaves to gullible people who thought that this radiation might hurt them.
It's my understanding that the holes are there merely to be able to see in. Microwave ovens work in the 2.4GHz range, whose waves are a good deal longer than visible light waves. So, if the holes are small enough to keep the 2.4GHz waves contained, but large enough to allow visible light through, then they do their job correctly. At 01:14 PM 1/28/2014, Dan Asimov wrote:
OK, just one question: Does the basic design of a microwave oven require that the interior have holes in it? Those holes make it inevitable that as time marches on the oven starts to stink.
--Dan
On 2014-01-28, at 12:43 PM, Tom Knight wrote:
No excuses for the user interfaces. For the inner surfaces, however, Im pretty sure they are intended to randomize the distribution of reflected internal radiation, which would, with smooth surfaces, likely bounce in very predictable ways, leading to local hot spots and cold spots.
* Dan Asimov <dasimov@earthlink.net> [Jan 29. 2014 09:10]:
OK, just one question: Does the basic design of a microwave oven require that the interior have holes in it? Those holes make it inevitable that as time marches on the oven starts to stink.
Put bleach (hospital grade, non-perfumed) into a pump-spray bottle. Thoroughly spray inside. Close microwave; wait an hour. Wipe residuals (bleach turns into salt, nothing to be worried). Operate microwave with a glass of water in it (never empty!), let the water boil. Wait 5 minutes to let water vapor moisten the oven. Wipe again. Leave microwave open over night to let the lovely chlorine smell disappear. Profit! Alternative: Disassemble as far as needed and clean parts. Can be anywhere from easy to quite impossible. This, however, does not involve smelling chlorine, which is a bit sad. Best, jj
--Dan
Sounds like a good plan. (But, do I ever hate chlorine!) --Dan On 2014-01-29, at 12:47 AM, Joerg Arndt wrote:
Put bleach (hospital grade, non-perfumed) into a pump-spray bottle. Thoroughly spray inside. Close microwave; wait an hour. Wipe residuals (bleach turns into salt, nothing to be worried).
Operate microwave with a glass of water in it (never empty!), let the water boil. Wait 5 minutes to let water vapor moisten the oven. Wipe again.
Leave microwave open over night to let the lovely chlorine smell disappear.
On 1/28/2014 12:43 PM, Tom Knight wrote:
No excuses for the user interfaces. For the inner surfaces, however, I’m pretty sure they are intended to randomize the distribution of reflected internal radiation, which would, with smooth surfaces, likely bounce in very predictable ways, leading to local hot spots and cold spots.
A lot of them used to have metal "paddle" that rotated like the carousel. It's function was to keep changing the shape of the resonant modes so as to even out the heating. Maybe the carousel itself serves that purpose on ones without the "paddle". Brent
participants (7)
-
Bill Gosper -
Dan Asimov -
Edward Fredkin -
Henry Baker -
Joerg Arndt -
meekerdb -
Tom Knight