Is the Force on a Dam dependant on the height of the water or the amount of water?

  • Thread starter peanutaxis
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Just had this pondering: Does the force on a water dam depend merely on the height of the water column behind it or does it depend on the total amount of water behind it? For the same dam if I have a lake behind it that is just a few metres wide vs. having a vastly large lake behind it with the same height.

Initially I want to say that the pressure at any given depth is dependant on water height/column only, so the force on the dam would be the same no matter the size of the lake, But that doesn't feel right somehow....
 

Baluncore

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Only the hydrostatic pressure due to the height is important.
 

berkeman

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Initially I want to say that the pressure at any given depth is dependant on water height/column only, so the force on the dam would be the same no matter the size of the lake, But that doesn't feel right somehow....
Remember that Force is Pressure x Area. In your question you ask about "Force", but I think you really mean Pressure.

The length of the lake behind the dam would not matter, but the width of the lake at the dam (and hence the width of the dam) would change the total "Force" on the dam, but not the max pressure on the dam base. Does that help?
 

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