# Metric system help

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Any good tips/sights to help teach it?

My son is having troubling with it. We are covering just the four basics, meter stick, graduated cylinder, thermometer, and gram scales. However, he can only recall we use a thermometer for temperature :glare:

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The complaint I hear most often is that people don't have a feel for what these numbers mean the way that they do for Imperial or U.S. units. I think it may be because we teach it as a one-off before going back and not thinking about it again. What I do instead is actually use the metric system, for cooking, in measuring for curtains, in my thermostat and anytime I look up weather forecasts online.

Here are a few tidbits which help to put things in perspective.

On the temperature scale, it's useful to own Celsius thermometers. I have one in most rooms of the house, and I keep one monitoring the outside. This way I have learned what degrees Celsius feel like. Here's a quick mnemonic to get started:

30 is hot,

20 is nice,

10 is cold,

0 is ice.

Everyone is accustomed to the fact that the average human temperature is 98.6 Fahrenheit. Where does that odd number come from? It's converted from a rounder number in Celsius:

37 C = 98.6 F = Average human body temperature

38 C = 100.4 = The start of a fever

40 C = 104 = The starting range of a fever that could cause brain damage

The very specific numbers you get by converting these temperatures to Fahrenheit disguise the fact that they are actually arbitrarily chosen to be nicely round numbers on the Celsius system, making the Fahrenheit numbers look artificially precise.

As for mass, of course water weighs 1 gram per ml. But in fact, most household liquids are close enough to this density that this holds true enough to gain a general idea of the relation of volume to mass for many tasks in the kitchen. I personally think everyone should own a digital gram weight kitchen scale. I have a book called Ratio, which has a lot of basic recipes translated into the underlying weight ratios, and this makes cooking a lot easier, and could also be helpful in developing a sense of measurements through use.

Here's a useful tidbit for getting familiar with the 'feel' of gram weight: the US nickel weighs 5 grams by specification.

For length, it is helpful to remember the specifications for the very familiar CDs and DVDs. They are 12 cm across. The hole in the middle is 2 cm in diameter. That makes the distance between the outer edge and the hole 5 cm.

I don't recall at what age I could do money computations, but it is handy to keep in mind that if you ever need a rough idea of how a specification in inches relates to centimeters, you can think of inches as quarters and centimeters as dimes. If you have 46 quarters, you can work out that it amounts to \$11.50. Now convert to dimes -- 115. 46 inches is about 115 centimeters.

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What exactly are you trying to teach? In 2nd grade, I'd not go with formal conversions between the systems, but, as other people said, develop a feeling for the meaning of the units.

a kilogram is 1,000 gram and corresponds roughly to the mass of two 1lb cans

a 2 liter soda bottle has a mass of 2kg or 4 lbs

a gallon is a bit less than 4 liters and has a mass of a bit less than 4kg

a liter is roughly the same as a quart or four cups

a meter is roughly the same as a yard

a mile is a bit more than a kilometer and a half

the side of a sugar cube is 1.5 centimeters long

the long side of a sheet of letter size (8.5in x11in) paper is 28 cm long

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