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How Does Fluid Momentum Work?

Water can be your best friend or your worst enemy

Even been in a shower where the showerhead water pressure is so high that it feels like you’re being struck by needles all over your body? Or imagine having a high velocity sprinkler hitting your bareback. Ouch. Who knew that water could actually be a pain? Well, this is all due to a fluid property known as fluid momentum. That’s right, you heard it right. Rigid, solid objects are not the only things that can carry momentum. My hope is that I am able to give a very general overview of fluid momentum, as the more specifics behind it will be covered in a fluid mechanics course.

How does it work?

Well any fluid that is traveling with a velocity through a certain area has flow, Q. That fluid also has a density associated with it, so since density is mass over volume

Density= mass/volume

When you multiply Q by density, you get mass over time. In fluid mechanics, we refer to this as mass flow rate, the rate at which mass of your fluid is changing over time. Now imagine this mass flow of a fluid that moves within a volume, like through a pipe….so its essentially a volume of mass coming out of a pipe.

What else could it be possibly used for?

It’s exactly why when water hits you with a high enough flow it feels like it hurts, almost like a block is hitting your skin…constantly. But what else can it be used for? Well, one of the main things that it is useful for is for force calculations on pipes moving large amounts of water through bends. If you can calculate the fluid momentum of the water moving through a pipe bend, then you can determine the sizing of the pipes as well as the type of material needed for the pipe to handle that water movement. What do you think are other possible uses of fluid momentum in real life?

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