– Bar (pressure) and size/width


Hello everyone.

I have a question, which I have no idea how to search for, regarding pressure.


1 bar is equal to roughly 10 metres of water

If I have 2 different pipes with water, first is Ø10cm and second is Ø10m, will both have 10 metres of water with 1 bar or will they be different?


The way I understand it, bar is “overpressure” (or underpressure), which means both pipes will have 10 metres of water with 1 bar, but the bigger pipe requires more energy to get to 1 bar, compared to the smaller pipe.


I’m really bad at explaining, sorry for that.

In: 1

Are the pipes vertical or horizontal? Are they under external pressure or are we only talking about pressure from the weight of the water? You’ll need to provide a bit more background info to explain what you mean.

Pressure is determined solely by depth.

So yes, your 10cm diameter pipe and your 10m diameter pipe would have the same water pressure at the bottom when they have the same depth of water.

Water pressure is essentially the weight of all the water ABOVE the point that you are measuring at, the water to the sides doesn’t matter. So it doesn’t matter how wide your pipe is, if you’re 10m underwater it will be the same water pressure.

Remember that essentially
pressure = weight(force) / area.

So yes making a bigger pipe mean the total weight of the water is more, but there’s also a bigger area at the bottom holding that weight.

The diameter doesn’t matter.

The pressure is the same 1 meter under water if you are in a pool or out in the ocean (if both are equally salty and have the same temperature). The ocean is a lot bigger than a pool but the pressure at depth is the same.

Pressure is force per area.

If you change the size of the area and at the same time change the force at the same rate it cancels out.

Imagine carrying someone on your shoulders. Now there is a second person carrying someone on your shoulders next to you.

In which case where you carrying more? when you were alone or when there were two of you carrying twice the amount?

It equals out.

If you have a bigger pipe you will need more energy to pump water up into it and there will be more force pushing down on the bottom but the pressure stays the same.

The important bit here is Pressure = Force/Area

The bigger pipe has 10x the diameter so it holds 100x the water, this means that the weight of the water and the force at the bottom of it is 100x higher than in the narrower pipe

But the bigger pipe also has 100x the area at the bottom so the pressure is the same (100x force)/(100x area)=1x pressure

You could have a super wide pipe and a super narrow pipe and as long as they’re filled to the same height the pressure in both is the same, but the force at the bottom will be wildly different