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# is my laziness acceptable?

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Hi There,

Quite often I write my expressions like the ones below:

I write it as: 1000N * 3m = 3kNm

is this incorrect as I haven't written the *10^-3?, that is;

1000N* 3m *10^-3 = 3kNm

or another example with percentages:

I write it as: (5-4)/4 = 25%

is this incorrect as I haven't written *100%?, that is;

(5-4)/4 *100% = 25%

thoughts?

Mar 12, 2020
edited by vest4R  Mar 12, 2020

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Hi vest4R

The first one is confusing me.   where did 10^-3 come from?

1000N*3m = 3000Nm   (3kNm which is your notation but personally I don't like it much.)

However,

10^-3 = 0.001  it is not 1000

10N* 3m *10^-3 = 30Nm/1000 = 0.03Nm  NOT    3000Nm   and not     3kNm

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The second one is fine.

1/4 is the same as 25%

Mar 12, 2020
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Sorry melody. I meant 1000N ://. I've amended the original post.

vest4R  Mar 12, 2020
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No, I think you have made it worse.  it is the minus index that is wrong.

1000=10^+3

1000N* 3m *10^-3 =3000Nm/1000 = 3Nm  NOT   3kNm

Melody  Mar 12, 2020
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interesting. I see how you're getting confused.

This is how my teaching team have been writing their expressions over the years the

*10^-3 is meant to signify the coversion from 3000N to 3kN. It's not suppose to be a part of the mathmatical problem.

I hope that makes sence

vest4R  Mar 12, 2020
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To relate to the percentage example above,

"*100%"

I guess it could be written as "*10^-3kN"

vest4R  Mar 12, 2020
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"This is how my teaching team have been writing their expressions over the years "

Your teaching team needs to be shot!!!

Alan  Mar 12, 2020
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here's a good example from my lecturer. I just happen to have it open now.

vest4R  Mar 12, 2020
edited by vest4R  Mar 12, 2020
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You don't say what the units of 281.25 are.  Presumably they are kN.m. (Edited again!)

This means that 281.25 kN.m = 281.25*106 N.mm  or it could be written as 281.25*103 N.m

In terms of your original question you could have: 1000N*3m = 3000N.m or 3*103 N.m or 3 kN.m  but you should never see 10-3 appear anywhere here!

Alan  Mar 12, 2020
edited by Alan  Mar 12, 2020
edited by Alan  Mar 12, 2020
edited by Alan  Mar 12, 2020
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I'll second Alan's sentiment!

Melody  Mar 12, 2020
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You:

"interesting. I see how you're getting confused.

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I hope that makes sense"

My response:

You may find it 'interesting' but I do not think it is me who is confused.

And no, what you have written does not make sense.

Melody  Mar 12, 2020
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I can see exactly where you're coming from. I believe that this issue so systemic throughout my facilty that most (including myself until now) do not know we're writing it incorrectly. I can see your way as correct.

I guess we've essentially made our own language while being oblivious to it.

vest4R  Mar 12, 2020
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ok

Melody  Mar 12, 2020
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Thanks for your help guys. I appreciate the insight into mathmatical correctness.

This is a typical example of how engineers butcher math lol.

Mar 12, 2020