How many drops of water is needed to give a stone a dent/hole?

The above answers have mentioned is a kind of thought that I have. Similarly,I hold the point. It can be divided into two aspects. One is called "quantitative change". The other is "qualitative change". The key of a drop of water transforms an intact stone into a stone which has a hole. Finally,Thanks for your invitation.

The phenomenon about which you are asking is called weathering which is breaking down of rocks , soil and minerals through contact with the wind , biota and waters. However, if you consider the science behind drop of water making a hole in stone, it will depend upon the pressure being applied by drop of water on stone, the material of stone. A point to note is that weathering occurs in site or with no movement and should not be confused with erosion , which involves the movement of rocks and minerals by water , wind, etc.

It takes a long time for a visible dent to appear. What happens is that the water droplet would fall on the rock with some force. this force separates a very small piece of the rock and the small piece flows off with the water. Over time, when a great many droplets fall on the same spot, a lot of small pieces of the rock are eroded. This is how the perceived 'dent' is formed on the rock. So technically, just one is enough, while it would take millions of drops to visually observe the so called 'dent'

It depends on the type of stone firstly ,how thick it is and the purity of water,how much hard it is,salinevor not,acidic or not etc,if acidic water falls on marble rock it will be easily get damaged that is it gets holes http://easily.In case of acidic water and marble stone if the water runs continuously ,then also the same thing can happen, I doubt about other combinations. And I am not shure about the number of drops needed for that ,obviously the number must be huge one,because I have noticed that rain drops falling on ordinary rock found in my region(kerala, india) made slight deformation only after 4 or 5 years, I also noticed in really old temples in kerala the pavement rocks near to temple building have small dips on them caused by rain drops falling from roof,and in kerala we get almost 5 minths rain every year sometimes 6 months,on an average we may take 5 months for avoiding any over calculations,everyday maynot rain so we assume 130 days of raining,and it wont rain 24 hours so we assume it is equal to about 50 days continous rain, so we may get 1200 hours of rain yearly. Now in an hour howmany drops can fall on a stone (here the stone is directlybelow the roof of temple so drops fall on stone at same spot at almost same time interval)? If it is moderately raining drops may fall 1 drop per sec on an average,so it amounts to 4,320,000 drops a year . Now within 5 years it made a small 2mm or 3 mm dip on the stone ,that is, a number of 21,600,000 drops made thatmuch small dip.Now you may calculate approximate number of drops needed to make hole on your stone. (All calculations and values are approximate since actual data is unavailable for me, I apologize for that)

Water gives rocks dents or holes because the water erodes the rock as it falls onto it. But if water was to erode a rock it would have to be a continuous stream of constant water or a lot of steady rainfall. But each rock would erode differently, a block of sulfur would erode much faster then a chunk of diamond.

Hi Ivan, Thanks for A2A. Let me put this in another perspective rather than the literal one. Every drop (effort) count till you make the dent (reach the goal). Effect of first one may not be seen, or may be to small for us to see. But it doesn't mean it meant nothing. Longer the duration of stream (struggle) closer you get to break it. Longer pause you take, more you have to redo.

I don't have a specific answer and am tempted to answer, "Ask Mr. Owl" and the answer would be 3.  I'm sure there are many factors including hardness of the water, the height of the drop, and type of stone.  The type of stone would make a huge difference..........sandstone can be broken by hand, whereas granite is very dense.

The question strangely reminds of Kidney Stones, formed due to Lack of water. So I would recommend  plenty  of water in gallons, to not only create  dent but to remove  the stone!!!

It depends on the stone composition, water acidity, speed, volume and frequency of the drop, I guess.