Exactly. And since 628t is NOT a pure number (it has units of time), it CAN'T be the argument to sine or any other transcendental function.

See my answer in post #34.

Bob

 

Anybody who does not recognize the variable 't' as units of time in seconds has GOT TO BE KIDDING or way overly PEDANTIC.
't' is time in seconds when there is no other information present.
For example, do you really think time 't' could be in units of time in centuries? If you say that's possible you have no common sense relative to electronic studies. Even if you say 't' is time in weeks that's still stretching it.
But hey it's up to you declare whatever you wish but you just make this much much more complicated than it needs to be.

Why do people bend over backwards to justify continuing to be lazy and sloppy?

I have worked on systems where 't' was in minutes. I have worked on systems where 't' was in microseconds. It is VERY common for systems to use a unit of 't' that is keyed to the sampling period.

Furthermore, sine functions are used for all kinds of things that don't involve only time -- such as the voltage along a transmission line. There it is a lot harder to guess the units that were intended -- meters, inches, millimeter, microns, angstroms, miles -- all of those are scales at which such problems are worked. If people are sloppy with their time units in trig functions, they WILL be sloppy with their length units as well. I've seen it over and over and over.

I simply do not understand this attitude that says, "I assume that everyone else that sees what I write will assume that I am using seconds for time, therefore it is perfectly acceptable for me not to use units."

What is SO hard about using units properly?

 

Well actually i forgot the little degrees symbol that is the real second form i meant.

And I would suggest that one of the reasons that you likely forgot it is that you (like most people) are, in general, sloppy with your units. You have not trained yourself to pay attention to them at all time, and so even when you mean to use them it is easy to neglect doing so and hard for you to catch because no red warning flags go up.

 

And I would suggest that one of the reasons that you likely forgot it is that you (like most people) are, in general, sloppy with your units. You have not trained yourself to pay attention to them at all time, and so even when you mean to use them it is easy to neglect doing so and hard for you to catch because no red warning flags go up.

Ok thanks for the free psychology session

 

And I would suggest that one of the reasons that you likely forgot it is that you (like most people) are, in general, sloppy with your units. You have not trained yourself to pay attention to them at all time, and so even when you mean to use them it is easy to neglect doing so and hard for you to catch because no red warning flags go up.

Why to you feel it is necessary to criticize "most people" when you are addressing one person? Seems like a rather sloppy generalization by you.

 

Ok thanks for the free psychology session

You're more than welcome.

While I know that you aren't about to change your ways, hopefully there will be some folks that come across this that are at the right stage in their learning curve -- far enough along to have been bit by not tracking units many times while not so far as to have become irreversibly invested in believing that how they currently do things is the best way to do it -- to benefit from it.

And, no, that is in no way meant as a slight against you -- it's how most humans, including me, usually function. Something that we have done successfully for years becomes an ingrained way of doing things and we will tend to defend it as being perfectly correct and acceptable no matter how many flaws and pitfalls are pointed out to us. It can take something drastic, like the person standing next to you getting killed because they didn't track their units, to make you re-evaluate how you do things. Only in hindsight as you start reaping the benefits do you start to realize how truly limited your prior success actually was (or at least how much easier achieving it could have been).

One of my professors went all Nazi on us about units (which I was already very good about, but not yet a religious zealot) -- and stayed there. We either truly tracked units at each and every step of each and every problem or he simply gave us a zero on it (even if it was on an exam). That semester I went from being a 3.6 student to a 4.0 student. Years later I went back and thanked him, and I was a bit surprised by his reaction. Some of my most treasured professional moments have been the handful of times when one of my students has come back and thanked me for exactly the same thing, and after the first time I fully understood and appreciated his reaction.

 

Why to you feel it is necessary to criticize "most people" when you are addressing one person? Seems like a rather sloppy generalization by you.

Because I am making a point that applies to most people. Most people ARE very sloppy with their units.

 

You're more than welcome.

While I know that you aren't about to change your ways, hopefully there will be some folks that come across this that are at the right stage in their learning curve -- far enough along to have been bit by not tracking units many times while not so far as to have become irreversibly invested in believing that how they currently do things is the best way to do it -- to benefit from it.

And, no, that is in no way meant as a slight against you -- it's how most humans, including me, usually function. Something that we have done successfully for years becomes an ingrained way of doing things and we will tend to defend it as being perfectly correct and acceptable no matter how many flaws and pitfalls are pointed out to us. It can take something drastic, like the person standing next to you getting killed because they didn't track their units, to make you re-evaluate how you do things. Only in hindsight as you start reaping the benefits do you start to realize how truly limited your prior success actually was (or at least how much easier achieving it could have been).

One of my professors went all Nazi on us about units (which I was already very good about, but not yet a religious zealot) -- and stayed there. We either truly tracked units at each and every step of each and every problem or he simply gave us a zero on it (even if it was on an exam). That semester I went from being a 3.6 student to a 4.0 student. Years later I went back and thanked him, and I was a bit surprised by his reaction. Some of my most treasured professional moments have been the handful of times when one of my students has come back and thanked me for exactly the same thing, and after the first time I fully understood and appreciated his reaction.

Well thanks for the explanation, but what really happened was i just assumed that anyone that saw pi/4 and 45 in the two equations would automatically recognize the 45 as being equivalent to the pi/4 especially since i noted that they were "two forms" which really implied two forms of the same thing.

Also, i would have probably typed "deg" or "degrees" because i am not sure where to find that little "O" degree sign on here as i dont usually need it (typing "degrees" most of the time).

Note also that when the inference is not immediately recognizable i will in fact type "degrees".

 

Because I am making a point that applies to most people. Most people ARE very sloppy with their units.

You dont think you are being a bit overly pedantic though?
On the other hand, maybe we need somebody like you to keep pointing this out. If you were around before the 100 million plus dollars Climate Orbiter launch maybe there would not have been a mistake in units conversion and it would not have crashed which would have meant all that money would have been well spent.

 

Well thanks for the explanation, but what really happened was i just assumed that anyone that saw pi/4 and 45 in the two equations would automatically recognize the 45 as being equivalent to the pi/4 especially since i noted that they were "two forms" which really implied two forms of the same thing.

Also, i would have probably typed "deg" or "degrees" because i am not sure where to find that little "O" degree sign on here as i dont usually need it (typing "degrees" most of the time).

Note also that when the inference is not immediately recognizable i will in fact type "degrees".

But notice that this is exactly what I was referring to. We get sloppy about how we do something and get in the habit of relying on assumptions about what other people will assume, that even when we mean to explicit we tend to follow our normal habits and, because it is what we are used to, it is hard for us to spot that we did so.

Ask almost any carrier pilot how they land on a nice, long runway in the middle of the desert and they will tell you that they land just like it is a carrier in the middle of the ocean. The reason is simple -- when they go back out to a carrier, they don't want to assume that they are going to remember that they are no longer landing on a nice, long runway in the middle of the desert.

 

You dont think you are being a bit overly pedantic though?
On the other hand, maybe we need somebody like you to keep pointing this out. If you were around before the 100 million plus dollars Climate Orbiter launch maybe there would not have been a mistake in units conversion and it would not have crashed which would have meant all that money would have been well spent.

It's actually possible -- but far from guaranteed. The underlying units issue was buried pretty deep in some software that had been adapted from another project. But I've always maintained that had either Lockheed or NASA (preferably both, of course) fostered a culture of strict adherence and observation to properly tracking units that the mistake almost certainly would not have been made or would have been caught in one of the design reviews.

I freely admit that I am an over-the-top units nazi -- and I make no apologies for it.

I HAVE caught errors during design reviews (including in one case the day before chip submission) as a result of my tendency of harping on the information presented on slides that don't reflect proper tracking of units, without even seeing the actual work. Because of this I started getting asked to attend the design reviews of the company we shared office space with.

I've become so units-conscious that I simply can't ignore them. A common example is if a current-controlled voltage source says that the output is something like V = 2·Io. If I'm working that problem, or reviewing someone else's work, I can't proceed like that even if I consciously try -- I would have to completely strip all of the units out of the problem, and even then it would be uncomfortable. I have to rewrite that as V = (2Ω)·Io (while cringing because it is forcing me to make assumptions that I should not be having to make just because the person that wrote the problem is ignorant/sloppy/lazy/whatever).

Another place you see it regularly is in exponentials. People will calculate an RC time constant of 2 seconds and then write the exponential as exp(-t/2). I can't work with that. I have to add the units. This is also a place where I commonly find mistakes that people make and don't catch because they won't track their units. They will put exp(-2t) and keep slugging along. This is particularly a problem when the time constant is a fraction, say ½ second, Because they also tend to want to do as many steps in their head as they can and because humans aren't usually very good about dealing with fractions in the denominator of another fraction, they will get it wrong. Had they tracked their units they would likely have immediately seen that they don't work out and they almost couldn't have avoided seeing eventually that they are trying to take the exponential of so many square-seconds.

I frequently go so far as to invent units to add the extreme error-detection power of units tracking to more complex problems that don't involve units, such as a pure math problem.

For instance, applying this to a simple problem that I normally would not go down this road for, if I had something like

30 = 2x² - 5x - 12

I would assign x units of A and the 2 units of B, giving

30 BA² = (2 B)x² - (5 BA)x - (12 BA²)

Solving it we now have

(2 B)x² - (5 BA)x - (42 BA²) = 0

x = { -(-5 BA) ± √[(-5 BA)² - 4(2 B)(-42 BA²)]} / [ 2(2 B)]

x = { (5 BA) ± √[(25 B²A²) + (336 B²A²)] } / (4 B)]

x = { (5 BA) ± √(361 B²A²) } / (4 B)]

x = { (5 BA) ± (19 BA) } / (4 B)]

x = { (5 A) ± (19 A) } / 4

x = (24/4) A, (-14/4) A

x = 6 A, -3.5 A

Since my answers have units of A, which is the units I assigned x, the units work out.

If I make a mistake along the way, it will usually (not always) mess up the units and I usually catch it immediately, while I'm writing the line I make the mistake on.

In fact, in working this problem while typing it out I made such a mistake and caught it precisely this way.

 

Why do people bend over backwards to justify continuing to be lazy and sloppy?

I have worked on systems where 't' was in minutes. I have worked on systems where 't' was in microseconds. It is VERY common for systems to use a unit of 't' that is keyed to the sampling period.

Because context us meaningful here. The question was asked in the context of a physics class. Physics classes are taught with a consistent set of units.

In my high school class, mechanics was taught using imperial units (feet, pounds, seconds). My college courses usually used MKS (meters, kilograms, seconds), except for my electromagnetism class which used CGS (centimeters, grams, seconds). This latter system has the unit of capacitance be, bizarrely, centimeters!

But notice that all of them use seconds as the unit of time, @MrAl had some justification for his statement.

In another context, different defaults would apply. In an American PCB design company, they might use mils as the unit for trace widths, whereas anywhere else in the world it is likely millimeters. In each case, the practitioners would not likely write mils or mm after each trace width referenced. Sloppy? Maybe so, but not ambiguous to the people involved.

Bob

 

Sloppy? Maybe so, but not ambiguous to the people involved.

Except when these different groups of practitioners interact with each other, and still believe nothing is ambiguous. It can lead to inter-planetary disaster.

Why the Mars Probe went off course
https://spectrum.ieee.org/aerospace/robotic-exploration/why-the-mars-probe-went-off-course
...
"NASA assigned three separate teams to investigate the embarrassing, US $125 million debacle and determine its cause.
Preliminary public statements faulted a slip-up between the probe's builders and its operators, a failure to convert the English units of measurement used in construction into the metric units used for operation."