Dimensional Analysis/ Unit conversion  [ENDORSED]

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Dimensional Analysis/ Unit conversion

Postby AmandaRae » Sun Jul 02, 2017 10:33 am

I know there are a lot of posts on here about unit conversions, but I'm having a problem specifically with long dimensional analysis. Is there a need to do all of the conversions in one giant step, does it make it easier to visualize? I tend to break it up into smaller steps, which in the long run takes a little longer. But most definitely as of the moment i'm having trouble converting from like picometers to nanometers and vice versa etc... for some reason I'm struggling with this, and converting ounces to grams, and mph to m.s^-1. Anyone have some tips or tricks ??? It would be greatly appreciated!!! (:

Chels Zh 1D
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Re: Dimensional Analysis/ Unit conversion

Postby Chels Zh 1D » Sun Jul 02, 2017 12:08 pm

Hi there, it's not a problem of using whether one giant step or breaking up into small parts, I feel like it is just personal preferences, for me, I like to classify the same type together on the same side, getting easier to visualize. And for instance, it is always useful to use the SI units as the central conversion; you can convert any unfamiliar units to their SI units first, then proceed to the next one. For converting picometer to nanometer, you can convert pm to m first, which is 1e-12, then nm to m, which is 1e-9, then 1 pm to 1 nm is simply 1e-3. I hope this helps. :))

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Re: Dimensional Analysis/ Unit conversion

Postby Gwyndolyn » Sun Jul 02, 2017 12:19 pm

I think it's fine to break up long dimensional analysis problems into parts, but it does take a little longer. I used to do it in parts but the more used to the problems you get, the easier it is to write it out all together. When writing out the problem just think how many steps you need for get to the answer, then you know how many sections you'll need in the problem and it makes it harder to forget a step. You also can see how all the units are canceling out to leave you with the ones you need for your answer.
As for tips for conversions, for picometers , nanometers, etc. I would say to make sure that you put the number you're given into 1*10^-9 (or whichever unit it is) form. And be careful, if the number is, say 350nm, then it's going to be either 350 *10^-9 or 3.50*10^-7, but not 3.50*10^-9. Sometimes, depending on what the conversion is, you might need to first convert it to the meters, and then to the desired units. If you're having trouble with it I think drawing the tables that are used in long dimensional analysis help because you set it up so that the units you have cancel out and it helps you understand how you move from on unit to another.
Sorry, this isn't that helpful, but doing a lot of problems does help you get more used to it, I think.

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Re: Dimensional Analysis/ Unit conversion

Postby Chem_Mod » Sun Jul 02, 2017 1:24 pm

Easier and less likely to make mistakes if one:

A. Converts given numbers to SI units.

B. Use the numbers in SI units in your problem/calculation.

C. Check units cancel in your calculation.

D. Check unit in final answer and does it make sense.

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Re: Dimensional Analysis/ Unit conversion

Postby mayasinha1B » Tue Oct 03, 2017 10:06 am

If visualizing it and writing out all the steps helps you see it all better, definitely do it. The extra 15 seconds it takes would definitely be better than missing the points for the right answer. I also find that I tend to do that and it's saved me from many careless errors.

Hellen Truong 2J
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Re: Dimensional Analysis/ Unit conversion  [ENDORSED]

Postby Hellen Truong 2J » Sat Oct 07, 2017 9:49 pm

My TA showed us this method for dimensional analysis called a ladder! You can easily convert to different units by writing out your "given," and then matching conversion units to it by just writing the units so that they cancel out. Every unit should cancel out diagonally if you match all of them correctly, and I find it easier to just write out all the steps so I don't get confused and I can check my work more effectively.

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