In an old fashioned timer that uses sand falling down into a tube does the rate of sand falling increase, decrease or stay the same as more sand falls?
by 
jack-is-moppy
ANSWERS: 3
-
Hhhmmm. This question is difficult to answer using mathematical and logic reasoning. One needs to factor in the pressure of the sand above and the frictional force between grains of sand, looks like they would cancel each other, but might not completely. Good question in physics.
-
If it were a liquid instead of sand, the higher pressure when the upper chamber is full would make it flow faster than when the upper chamber is nearly empty. But grains of sand behave differently. I think the system is designed for the sand to flow at a fairly constant rate independent of level, though I can't offer a mathematical explanation.
-
I think it's more or less the same. The reason is that sand grains distribute the weight fairly evenly around their neighbours, so most of the weight of the sand at the top gets distributed to the sides of the tube. Imagine a tall cone of paper, a "dunce hat", at the bottom of a glass tube. Fill the tube with sand. If the paper cone is steep enough it can support the sand: each sand grain next to the paper is transferring most of the weight to the sand grains below it, and only a fraction onto the paper. In the sandtimer - the paper represents the cone shaped area where there is very little force between the grains, just above the constriction. As sand escapes, the tiny force that supports the cone above gives way, and the cone collapses in, flooding the cone region with sand, but instantly another cone is formed. I have a small one of these sandtimers and I just got it out and attempted to see what's happening, but the sand is really too fine and whatever is happening at the constriction is too quick for me to see. Certainly the flow of sand seems constant.
RELATED QUESTIONS
Copyright 2023, Wired Ivy, LLC