The Perfect Geometry of Motion

I was reflecting today about the paranoia I've witnessed vis-a-vis the electric disposal units that keep people's drains from getting clogged with food refuse.

I think people base their mental-pictures of what is really happening on images they have formed when some metal object has inadvertently found it's way down the proverbial chute and clinked and clunked so loudly, and ultimately jammed the disposal.

While it's not a good idea to go putting your hand in there, unless you have long fingers, the most you will ever risk is touching the SIDES or the BOTTOM of a running disposal. Despite what one may have imagined, the central area of the disposal is relatively safe, because centrifugal forces created within the spinning DRUM (that cuts up the food) keep the center of the disposal generally free of dangerous (high-velocity) matter.

One design DOES use a free-spinning metal cog affixed to the spinning floor of the unit, and as you may have experienced, THAT DOES infrequently become jammed if it gets wrapped in a thread of synthetic matter.

Anyway the principle at work here is basic Newtonian physics, the idea that an object in motion tries to follow a course perfectly in line with the force that initially propels it.

To alter that course requires some LATERAL force. If you think about it, you'll realize that this is EXACTLY what a disposal unit does, it propels food in one direction, and then applies force to it to change its trajectory.

The persistent agitation (of the forces holding the food together) are disrupted and the matter simply falls apart.

Newton's Laws-of-Motion indicate that the forces can be produced by a small 1/2 horsepower engine spinning a 4-inch drum at high-speed.

Hence the modern disposal unit.

But as far as being proximately dangerous to flesh and bone, it's not...even when you are pressing a mass of food into it with your bare hand (but be wary anyway!)