Stable oscillation of a blanket in a dryer?

[Physics Monkey]

Hi everyone,

Today I noticed something curious while I was drying a blanket in a dryer. The dryer was turning and the blanket was jumbling around as usual, but then I realized the motion was approximately periodic. This periodic motion was strange to me.

Of course, the dryer is driven on a periodic cycle, but in my experience (not that I've really looked very closely), the clothes in the dryer usually move chaotically.

The blanket moved through a variety of shapes and around in the dryer over the course of about one second, then the whole process would repeat. I observed at least 20 periods of roughly the same motion. Afterwards I tried resetting the dryer and shaking the blanket, and when the dryer started again, there was no longer any stable oscillation.

Just curious if anyone else has ever seen something like this or knows anything about it?

It's funny because it really bothered my dog, the appearance of this rythmic and fairly loud beating noise.

 

[CWatters]

Yes I've seen it. Not that I make a habit of staring into a tumble drier :-)

Driers have paddles or blades so objects in the drier are lifted and then allowed to tumble/fall. There are two time constants 1) the drum/blade period and 2) objects period. What I think happens is that under the right conditions these two beat together or get in sync. Perhaps it occurs when the object lands in the same position with respect to a blade each time.

At resonance an oscilating system absorbs the maximium power from the driving source so not surprising if noise and vibration change at resonance.