Unit Conversions

[happycc]

Unit conversions have always made me cry. I suffered when having to learn dimensional analysis.

 

Is there a visual way to figure this out? Kind of like Thinkingblocks.com.

 

I have a hard time holding in my head that 1 kg is equal to 1000m and that if I wanted to convert 300kg how many meters--i have to ask myself well am i going from a bigger to smaller unit and then having to remember what is the bigger or the smaller unit and can't remember whether to multiply or divide UGH UGH UGH

 

 

Please help me so I can help my kids.

[Arcadia]

Bookmark for unit conversion http://www.nist.gov/...ad/bookmark.pdf

Pyramid for unit conversion http://www.nist.gov/...yramid-2002.pdf

 

Print both out and let your kids look at them while they do their math.

[Erica in OR]

Potentially way more information than you want. :)

 

I agree that having the unit conversions at hand is helpful; as you use them more and more from the paper, you'll start to automatically remember the ones you most commonly use.

 

My tips are to write it down, with each piece of the conversion steps shown as a block. My daughter's mistakes come when she tries to do ones with more than one step in her head. I also support the idea of working toward getting the units you don't want anymore to cancel out, as you move toward getting the units you want in the end.

 

For example, if I had 5 miles and wanted to get to centimeters.

 

(5 miles)

 

One of the conversions I have at hand is 1 mile = 5280 ft

I can write this as as a conversion factor with one or the other on top:

1 mile / 5280 ft

or

5280 ft / 1 mile

Both of these are equal to one, since the quantity on top is equal to the quantity on the bottom. So I can multiply my starting number by either of these factors because I'm not fundamentally changing the amount of stuff I started with, only the label. To get the miles label on my 5 miles starting amount to cancel on top, I need to choose the factor that has miles on the bottom. I add that to my string of steps.

 

(5 miles) x (5280 ft / 1 mile)

 

I also know that 1 ft = 12 in

My two choices of factors are:

1 ft / 12 in

or

12 in / 1 ft

To get the ft label on top to cancel, I need to use the factor that has ft on the bottom.

 

(5 miles) x (5280 ft / 1 mile) x (12 in / 1 ft)

 

I can then go from inches to centimeters. 1 in = 2.54 cm

My two choices:

1 in / 2.54 cm

or

2.54 cm / 1 in

To get the inch label I currently have on top to cancel, I need to use the factor that has inch on the bottom.

 

(5 miles) x (5280 ft / 1 mile) x (12 in / 1 ft) x (2.54 cm / 1 in)

 

Cancel labels:

miles on top cancels miles on bottom

ft on top cancels ft on bottom

in on top cancels in on bottom

label that remains is cm

 

Multiply all numbers on top and divide by all numbers on bottom.

Check if answer makes sense. Should there be more cm than miles? A lot more or just a little more?

 

Erica in OR

[letsplaymath]

This blog post explains the method Erica described. It may help you:

• How Old Are You, in Nanoseconds?
  

[regentrude]

I have a hard time holding in my head that 1 kg is equal to 1000m and that if I wanted to convert 300kg how many meters--i have to ask myself well am i going from a bigger to smaller unit and then having to remember what is the bigger or the smaller unit and can't remember whether to multiply or divide UGH UGH UGH

 

What you describe is impossible. kg is a mass and meters is a length. There is no conversion between them.

 

You may mean km.

What helps is to understand what the prefix means: "kilo" simply means "thousand".

So, 1 "thousand-meters"= 1,000 m , nothing to memorize, this is obvious.

And thus 300 "thousand-meters"=300,000m.

 

Likewise, centi means "one hundredths". milli means one thousandth. I suggest you learn the meaning of the prefixes - they will be the same for all units. There are only a few imprtant ones: Mega, kilo, deka, deci, centi, milli, micro, nano.

[Mandamom]

I use Math U See method

 

here it is explained..

 

http://www.mathusee....ew-lesson-8.pdf

 

I remember the order

 

King (Kilo)

Henry (Hecto)

Drinks (Deka)

Unbelievably (the unit)

Delicious (deci)

Chocolate (Centi)

Milk (mill)

 

My acronym is a little different than this one but here's the process.

 

http://www.wikihow.c...ic-Measurements

 

 

Knowing the greek and latin roots (Kilo = 1000) fills in the rest.

 

Once you understand the relationships you can move the decimals around pretty easily.

[Penguin]

I think the easiest way to begin to really understand (rather than just compute) dimensional analysis is to begin with time. Intuitively, you know that to change from hours to minutes you need to multiply by 60. So start playing around with time conversions, but write out every step.

 

When you are making a unit conversion, you are simply multiplying by 1.

 

(2 hours) (1)= 2 hours

(60 minutes/ 1 hour) is essentially just a "1"

(2 hours)( 60 minutes/hour) = 120 minutes

 

But, of course 1 hour/60 minutes is also a "1"

So how can I be CERTAIN that I should multiply by 60 rather than divide by 60?

Make sure that the units cancel and that what you are left with in the numerator is what you want for your final answer.

 

This web site has a good step-by-step tutorial with a good series of worked problems.

[happypamama]

Setting them up as fractions is the easiest way for me to show unit conversions as well, like Penguin said. Units cancel, and you're left with just one.

[happycc]

Renugrude...you are right. My bad. It is supposed to be Km. Grrr. typo erro in OP.