On Thursday 28 August 2008 14:41, Greg Freemyer wrote:
...
I try to move the laptop laterally (left/right, forward/backward) when possible. If I do have to lift it or rotate it while the disk is spinning, I do so very slowly.
My thinking is that the disk head is "flying" just above the platter. So a sudden up or down motion is more likely to cause the head to hit the platter. (a bad thing.)
Disk heads are under a balance of relatively strong forces (not to be confused with the Strong Force that acts inside atomic nuclei and within nucleons, of course). The arm mechanism presses the head towards the platter and aerodynamic forces cause by the relative motion of the platter and the head resist that force (commonly known as the Bernoulli force). The relative magnitude of the forces to due ordinary accelerations from movement of the device's enclosure are small in comparison to these and thus not likely to significantly deflect the head relative to the platter. Furthermore, any acceleration that deflects the head toward the platter causes an increase in the opposing aerodynamic force. Only accelerations characteristic of the end of a fall (dropping from 1G while at rest to zero during the fall and spiking sharply upward upon impact) are likely to deflect the head sufficiently to cause it to contact the platter. Of course, the instant contact occurs, it's all over and the drive is no more, at least as a data storage and retrieval device.
Since the platter is spinning, rotating the laptop will cause a gyroscopic force to try and accelerate the platter even faster. Not sure that is a big deal, but it makes me uncomfortable to think about. Somehow I just don't think a disk drive is designed to handle gyroscopic force. (Or maybe it is??)
The slowest drives in use today spin at 3600 RPM with 5400 RPM being typical. Many are faster and in desktops, workstations and servers the rotational speeds can range up to 15,000 RPM. In comparison to this, rotations cause by moving the drive enclosure are tiny. More significant, though still quite minor, are the forces of precession caused when the axis of rotation of the platter is changed. However, these forces resist any attempt to alter the orientation of the spin axis and actually act to counter any movement that might cause the head to move toward the platter. (This is the principle of operation for gyroscopes, by the way.)
Greg
Randall Schulz -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org