Vertical Velocity

[kmreid]

I was reading up on a few things, and I am still having trouble getting vertical velocity. The reason is because of this phrase on theweatherprediction.com, "The negative sign (on -ub/s) is used because pressure decreases with height in the atmosphere (usually when graphing, up is positive, but in this case, up leads to LOWER pressure). ub/s is made negative so upward vertical velocity can be given a positive sign.". Okay....so, I understand that the atmosphere's pressure decreases with height. Negative = lower pressure (which is higher UP in the atmosphere), and positive = upward velocity. So, how am I getting this confused? It seems like it is saying that both the negative and positive can indicate a vertical velocity that is moving upward. Can someone clarify? I am very visual when it comes to learning, and let's just say that physics can be a mental nightmare for me. Here is the link that I am referring to, http://www.theweatherprediction.com/habyhints/101/. I realize that I am probably oversimplifying things.

 

[MClarkson]

There are many different coordinate systems and frames of reference. The vertical reference point can be height (which goes up as you go up) or pressure (which goes down as you go up). Most systems are arranged such that positive vertical velocity implies upward motion regardless of which vertical reference is used, but this is not always the case. I agree, it can get confusing. I usually think of things simply as going up or going down, and try to leave the negative signs out of my mental picture.