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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

Hi Guys

I have something that has been bothering me for a few months now and the other day it popped up on a problem I was working on. The actual maths in terms of arithmetic operations was straight forward enough, but the solution was to be given in the correct units and I wasn't sure what they should be.

The example was as follows

where , andThe thing I have been wondering about is why some units are

and others . Does it mean the order of the derivative taken to calculate it?Thanks in advance.

David

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

Hi Dave;

Did we get the same answer?

rounded to 6.0 because of significant digit rules.

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**ZHero****Real Member**- Registered: 2008-06-08
- Posts: 1,889

ms[sup]-1[/sup] is same as m/s and so on...

no derivatives

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

Hi Bobby and ZHero

Yes, I got

, it asked for the answer to 3d.p.How is it that s is -2 though kg is -1. Does it just denote that m/s is a ratio and kg is a definite unit?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

Hi David;

Did you get the same units I did? 5.962 is 4 significant digits. Question is slightly off. You can never get more significant digits that than the least accurate input. In this case 9.8 is the least precise input with 2 significant digits. Therefore all rounding if I remember correctly is to 2 significant digits.

m/s is read meters per second.

**In mathematics, you don't understand things. You just get used to them.**

**If it ain't broke, fix it until it is.**

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**ZHero****Real Member**- Registered: 2008-06-08
- Posts: 1,889

DaveRobinsonUK wrote:

How is it that s is -2 though kg is -1. Does it just denote that m/s is a ratio and kg is a definite unit?

s is -2 coz its meter per second squared (unit of acceleration).

understand it like this..

As you can see, it appears to be a ratio but is rather a "Rate of Change w.r.t Time"!

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

Hi Bobby

Thanks for that, I didn't know about the accuracy. That's handy to know and makes sense too, kind of like Amdahls's Law for functions, although none of my tutors have ever mentioned it.

Just shows you that you should always consult others rather than taking one persons word for it.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

Hi Dave;

That's the general way with experimental data. Although you can ask for decimal points too.

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**If it ain't broke, fix it until it is.**

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

Ahh

I see now.

Unit for Acceleration (m/s)/s

Derived units.

Cool, happy now

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

How was Corsica!

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**If it ain't broke, fix it until it is.**

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**ZHero****Real Member**- Registered: 2008-06-08
- Posts: 1,889

DERIVED UNITS!!!!

that's Exactly what you call them!!

I had forgotten he he . .

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

It was great, until I was literally handing my passport over to the baggage handler when a woman leant over and wispered in her ear. She then said that all flights from Corsica to UK we cancelled for at least a week. There was a huge panic and a run on the airline desk. Luckily we have a house over there, so we just went home and had an extended holiday.

Took Emma to the beach everyday and made sand castles, and studied logarithms in the afternoons. Log fires in the evenings. Very nice

You off anywhere this year?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

Nope, no trips planned. So you had logs and logarithms. An extra week, sounds great.

**In mathematics, you don't understand things. You just get used to them.**

**If it ain't broke, fix it until it is.**

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

:P

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 98,182

Correct!

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**If it ain't broke, fix it until it is.**

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**leealden06****Member**- Registered: 2010-09-06
- Posts: 4

Scientific notation, also known as standard form or in exponential notation, is a way of writing numbers, which can contain values for large or small to be easily written in standard notation decimal notation.Scientific was developed to easily represent numbers are either very large or very small.Sometimes, especially when you use a calculator, you can come up with a very wide range.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,273

Hi Dave

Your log fire reminded me of the following:

bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**DaveRobinsonUK****Member**- Registered: 2010-04-24
- Posts: 123

Hi Bob

Sorry for the delay, been a while since my last post.

Love it :---- houseboat

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