the quartz analog clocks rely on an inexpensive quartz crystal which is probably+/-100 ppm, typically probably 20 ppm.
The AC synchronous motor clocks rely on the power company. I think most of the major AC power grids litteraly count the number of cycles in an hour and speed up or slow down slightly every hour to make the long term stability way better even than the short term stability. So that there are exactly 5,184,000 cycles in a day (60 Hz US standard).
2 stroke engines with reed valve intakes can run in either direction. One of my friends would start up model airplane engines, and they would sometimes get going the wrong way. He would throw a rag into the propeller to stop the engine so it could be restarted. So the bike engine running backwards is no mystery, if it's 2 stroke.
I assumed the DC adapter was for another appliance plugged into the same outlet as the clock.
I cannot imagine the adapter causing the grinding sound. My first thought is of a poor service connection. Plugging in the adapter caused an intermittant connect-disconnect (sparking) of the 110v service to the outlet. If you caught this motor just right, it could reverse it. You may also hear it as chatter or grinding in the clock. Not a safe condition.
I had an analog alarm clock that developed a similar tendancy to run the wrong way. What I found is that it had a synchronous motor that was equally comfortable starting and running in either direction, and it used a rachet mechanism to force it to only run in the desired direction. When the grease on the rachet mechanism thickened a bit it kept the rachet dog from engaging the wheel, and so the motor could now rotate in either direction.
There is no mystery at all why the clock ran backwards. There is a type of motor where the rotor is a permanent magnet inside an AC pole structure (like a "standard" synchronous motor). If the rotor is light enough, its vibration amplitude at 60 Hz will exceed a pole pitch. Such a synchronous motor will spontaneously start in a random direction. A ratchet mechanism forces it to reverse if it starts in the wrong direction. The drop damaged this mechanism, allowing the motor to start backwards.
You mean you don't just keep everything on GMT <vbg>? I only have about 6 or 7 "conventional" clocks (microwave, oven, coffe maker, cordless phones, ancient clock radio and an old VCR, etc.) and I just take my cellphone (the Verizon one, the AT&T Blackberry is way off) around with me.
Wal-Mart will hold its second Made in the USA Open Call July 7-8, at its headquarters in Bentonville, Ark. The event will be a repeat effort by the world’s biggest seller of consumer goods to increase the amount of US-made products it sells in Wal-Mart stores, in Sam’s Club members-only wholesale outlets, and on walmart.com.
From design feasibility, to development, to production, having the right information to make good decisions can ultimately keep a product from failing validation. The key is highly focused information that doesn’t come from conventional, statistics-based tests but from accelerated stress testing.
There’s a good chance that a few of the things mentioned here won't fully come to fruition in 2015 but rather much later down the line. However, as Malcolm X once said, "The future belongs to those who prepare for it today."
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.