LogFAQs > #983940078

ConfusedTorchic posted...

feel like it would be much simpler to power a small piezoelectric motor with a planetary gear system instead of needing a rock that vibrates and somehow makes gears move instead of the battery in it

Quartz *is* a small piezoelectric motor. The piezoelectric effect is what causes the deformation when voltage is applied and generates the voltage when it rebounds.

ConfusedTorchic posted...

then why have all those f***in gears and cogs in the watch

So that you only need one motor to turn everything instead of a series of electronic steps that convert the timing signal from the quartz into the movement of other hands. Turning 1 Hz into 1/60 Hz and 1/3600 Hz digitally isn't the easiest thing to do, since 60 isn't a power of 2. Turning 1 Hz into 1/60 Hz and 1/3600 Hz using gears, however, is relatively simple.

For digital watches, though, they often don't have all the gears and such because the signal can just be digitally translated into time.

ConfusedTorchic posted...

there's already mechanisms where you just turn a little dial and the watch functions for days, requiring no battery or quartz

there's even a variety of that that you don't even wind, it just works by wearing it

Yep, they function similarly: Winding the spring (whether manually or by a self-winding mechanism) provides the energy to turn the hands, and another component provides oscillating motion at a frequency that the rest of the watch translates into keeping time. Quartz is not the only way to do this, it's just a particularly reliable option that runs for much longer than non-self-winding watches can.

ConfusedTorchic posted...

so why is the rock necessary if you want a battery

It's not strictly necessary, but it is the simplest and most reliable option. As I mentioned, a fully-electronic LC circuit could do the trick, but would be much more sensitive to temperature fluctuations and harder to translate the higher-frequency oscillation into something useful for timekeeping. Quartz is used because it works well.

shadowsword87 posted...

Oh, it's not physically vibrating, it's electrically vibrating. Then other electronic stuff can read that vibrating voltage.

Actually, it is physically vibrating. That's the nature of the piezoelectric effect: it's translating electricity into physical movement and vice versa. It's a very small physical vibration, by virtue of being a very small piece of quartz and the relatively small amounts of energy involved in the vibration, but it's a vibration nonetheless.