About Hz and rad/s in mathcad

[ptc-2457460]

In MathCAD V14.0 M020,if you enter 1Hz,then press key"=",mathcad will give the result: 1Hz=1 1/s then we change "1/s" to "rad/s",the result is: 1Hz=1 rad/s I think that "1Hz=2*Ï€*rad/s",is mathcad si wrong,or I am wrong?

[RichardJ]

This has been discussed, ad nauseam, in the main forums: http://collab.mathsoft.com/~mathcad2000 If you want the long answer, go there and search the forum. In short, the SI definition of Hz is 1/s, and Mathcad is correct. So one Hz is one event per second, and the event could be anything. It might be 1 revolution of something, in which case the angular velocity is 2*pi*rad/s, but it might be something like 1 drip from a tap, which has nothing at all to do with angles. If you want the definition of Hz=2*pi*rad/s, which is nonsensical for anything that can't be described in terms of circular motion, use the Mathcad unit Hza Richard

[ptc-2457460]

Thank you. But in Control System,Bode graphics,the x axis "1Hz = 2*Ï€ rad/s". I know "1 Hza=2*Ï€ rad/s" in mathcad,but in my country ,people get used to using "Hz" as "2*Ï€ rad/s".

[RichardJ]

It's just a different unit system. The SI definition, which Mathcad uses, is Hz=1/s. There is a very good reason for that definition: it means the units of Hz can be applied to any periodic event. The definition of Hz=2*pi*rad/s can only be applied to events that can be represented in terms of circular motion. It is meaningless for any other type of event, because such events have no relationship to angles. Your country is no different to others. There are plenty of people in Taiwan that use the SI definition of Hz. As I said, this has been discussed over and over again on the main forums, by people from many countries. If you are describing, for example, a sinusoidal signal, or a rotating object, the definition Hz=2*pi*rad/s can be useful, and that's why Mathcad provides a unit Hza. If you want the unit to show as Hz, just put Hz:Hza at the top of the worksheet. Richard

[Philip.Oakley]

Yes, there is a problem, and not just with mathcad.... The thread mentioned has today http://collab.mathsoft.com/read?119886,19 got very close to answering the question, particularly with respect to how the SI committee left the problem... If you can manage to wade your way through the thread you will find it is mainly because we use less than rigourous formula for simple stuff like moments and arcs, and fail to indicate when a value is associated with an angle (rather than a number or a length etc.) It is like thermodynamics. You can't win. The best you could do is draw. The game is rigged. And you can't get out of the game.

[RichardJ]

"Philip Oakley" wrote:

Yes, there is a problem, and not just with mathcad.... The thread mentioned has today http://collab.mathsoft.com/read?119886,19 got very close to answering the question, particularly with respect to how the SI committee left the problem...

[Philip.Oakley]

"Philip Oakley" wrote:

got very close to .

[RichardJ]

"Philip Oakley" wrote:

I didn't say we'd cracked Zeno's paradox - still another half step to go 😉

[ptc-2010381]

What would be the proper way to establish a unit of revolutions per minute, RPM? I typically define RPM as 2*pi*rad/min at the top of my worksheet. In one particular worksheet I wrote this is causing some incorrect results. Will

[TomGutman]

anonymous wrote:

I typically define RPM as 2*pi*rad/min