Re: [Phys-l] accelerometers

[John Denker <jsd@av8n.com>]

On 11/23/2006 11:41 AM, Stefan Jeglinski hypothesized:

> If I hold such an accelerometer in my hand (so that it is attached to 
> my local reference frame), and suddenly an "ideal" trap-door in the 
> floor opens (t=0) and me and my accelerometer fall through "in ideal 
> fashion" (IOW pretend there is no drag, no rotation due to my spastic 
> twisting when I realize I'm falling, etc), I submit that the 
> accelerometer will not change its reading, even momentarily. From 
> t=0, every particle in the accelerometer and me are falling together, 
> and by looking at the accelerometer alone, it's as if we were still 
> standing on the floor.

This is an important and truly fundamental question.

I recommend you do some experiments of this type.  The trapdoor
version is inconvenient, but it suffices to dandle an accelerometer
up and down in your hand.

Also:  What do you think happens if you turn that accelerometer upside
down?  (See next note for more on this.)

Note that ordinary accelerometers (as shown in the picture) consist of
little more than a mass, a spring, some damping, and a readout mechanism.
 -- You can make your own accelerometer using a small mass, a rubber
  band, and a ruler.
 -- If you have spring scale ("fisherman's scale") and a suitable-sized
  mass, that's even more convenient.