How Can You Simplify Engineering Units in Calculations?

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Discussion Overview

The discussion revolves around simplifying engineering units in calculations, particularly focusing on how to handle composite units with prefixes. Participants explore methods for reducing units like Mg/ms into more standard forms, addressing both the removal of prefixes and the conversion to base units.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Casey seeks a logical method to simplify composite units, specifically wanting to avoid prefixes in the denominator except for kilograms.
  • Some participants suggest that removing prefixes is straightforward by using appropriate powers of ten, while reducing to base units may not always be practical.
  • Casey proposes a method involving rewriting the numerator and denominator in powers of ten to achieve a cleaner representation of units.
  • Another participant emphasizes the importance of returning to base units (kg, m, s) for clarity and suggests that keeping kg in the denominator is appropriate.
  • There is a discussion about whether to simplify units like mN/(kg*μs) to kN/(kg*s) and the potential implications of such simplifications on the final calculations.

Areas of Agreement / Disagreement

Participants generally agree on the importance of simplifying units to base forms, but there are differing opinions on the necessity and implications of removing prefixes and how to handle specific cases. The discussion remains unresolved regarding the best approach to unit simplification.

Contextual Notes

Some participants note that while simplifying units can help prevent errors, the context of the problem may dictate whether certain simplifications are beneficial or detrimental.

Saladsamurai
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Homework Statement



I am trying to get used to engineering prefixes and such. I would like to come up with a general way to reduce garbage composite units like Mg/ms into proper units.

Anybody have a general way. I know that my end result is to have no prefixes in denominator (except kg).

Should I break everything up into scientific notation and tryto build the denominator to the base unit (in this case seconds) or what? How do you go about these.

I am sure after awhile I won't even think about it, but for now I would like a logical method if possible.

Thanks,
Casey
 
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Do you mean just lose the multiplier prefix ( milli/micro/kilo etc) or do you mean reduce to base units mass/length/time etc ?

Removing the prefix is easy, just put the approriate powers of 10 and cancel.
Reducing to base units isn't always useful - no engineer wants a rate of pressure change in kg m^3 s^-3
 
mgb_phys said:
Do you mean just lose the multiplier prefix ( milli/micro/kilo etc) or do you mean reduce to base units mass/length/time etc ?

Removing the prefix is easy, just put the approriate powers of 10 and cancel.
Reducing to base units isn't always useful - no engineer wants a rate of pressure change in kg m^3 s^-3

The former. I have Mg/ms and I just want it to "look pretty".

So I should start with [tex]\frac{Mg}{ms}=\frac{1*10^6g}{1*10^{-3}}s=1*10^9\frac{g}{s}=\frac{1Gg}{s}[/tex]

So I could say in general: establish the base unit to be used in the denominator.
Re-write denominator as such.
Re-write numerator in powers of 10 of its respctive base-unit.
Work from there.

This should work.

Thanks,
Casey
 
What about 1 mN/(kg*mu s) Should I keep kg in denominator since it is base unit of mass? Or change to something else?

[tex]1\frac{mN}{kg\cdot \mu s}=1\frac{kN}{kg\cdot s}[/tex] or is this poor form?

Sorry guys, but get ready for lots of stupid questions! I am taking a directed study over x-mas break in Statics. I am only meeting with the prof 5 or 6 times. The rest is on me (with PF help of course:wink:)

Casey
 
Last edited:
You always want to get back to your base units. In your case kg, m and sec. All other units are going to be based on them. Unless you have special applications in which you already know the units will fall out for you.

When I come across problems with units like you have shown, the first thing I do is get rid of all of the prefixes, except for those on kg. Use those for all of your calculations and then convert back to prefixed units at the end. I find it too easy to make a mistake that will make you orders of magnitude off.

In your example above, make it:

[tex]1 \frac{mN}{kg*\mu s} = 1000 \frac{N}{kg*s} = 1000 \frac{m}{s^3}[/tex]

The last simplification may not be a good thing to do if you need the extra units to simplify the units at the end. That would be up to you.
 

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