Quick physics question... need clarification

[ptavasso]

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Hi everyone,
In the EK physics textbook, I read two statements that seem contradictory to me:
1) velocity increases as pressure decreases
2) velocity increases as depth increases

First of all, which equation are they looking at when they talk about depth: P=ρgh or P=ρgy? I'm guessing P=ρgy because it would make sense that increasing y (the distance from the top to the depth at the bottom, i.e. deeper down) will increase pressure- correct?

Second, I don't understand how both these statements can be true. If depth is increasing, then pressure is also increasing (I visualize this by thinking of the higher pressure at the bottom of the ocean vs. the top as well as using the P=ρgy equation)... so that would mean that velocity increases as depth (and therefore pressure) increases.

Please clarify these two statements as well as correct any incorrect thought process I may have. Fluids, pressure, etc. is the hardest physics topic for me

 

[Blueprint MCAT Tutor]

Hey can you give me the specific page # where you saw those statements?

The first statement I think assumes "all other things constant". So if a pipe is flowing horizontally along the ground, as the velocity goes up, pressure drops. P and v are inversely related.

I've never heard of depth being related to velocity in any direct way before. Usually depth is only concerned with gauge pressure and with buoyant force.

 

[ptavasso]

Hey can you give me the specific page # where you saw those statements?

The first statement I think assumes "all other things constant". So if a pipe is flowing horizontally along the ground, as the velocity goes up, pressure drops. P and v are inversely related.

I've never heard of depth being related to velocity in any direct way before. Usually depth is only concerned with gauge pressure and with buoyant force.

Hi thanks for the reply.
The first statement is on page 85 of EK Physics- first paragraph under the spigot diagram.
The second statement is on page 100 of EK Physics- first sentence after the "surface waves" paragraph.

Thank you!

 

[Blueprint MCAT Tutor]

Oh yeah okay they're talking about surface waves there. Very different thing, and 99.999% you won't get a question about that on test day. I think all they're saying is that a wave across the surface of a bathtub would be low compared to a wave across the surface of a swimming pool.

The swimming pool is deeper, so the waves moving along its surface are faster.

Really, don't even worry about it.

 

[ptavasso]

Oh yeah okay they're talking about surface waves there. Very different thing, and 99.999% you won't get a question about that on test day. I think all they're saying is that a wave across the surface of a bathtub would be low compared to a wave across the surface of a swimming pool.

The swimming pool is deeper, so the waves moving along its surface are faster.

Really, don't even worry about it.

I understand now that it is in two different instances (first one is linearly, as in a pipe, and the second one is vertically, as in the ocean).
Thanks again