Introduction to Measuring Weight

When you go to the shop to buy a vegetable, you need to tell the shopkeeper whether you need half a kilogram of cauliflower or a kilogram of potatoes. While doing Chemistry experiments, every gram of the various compounds and mixtures need to be taken in the correct weight and measure, for the experiment to proceed smoothly. These are just a few examples which show how important it is to be able to measure weight accurately.

The Big Idea: Measuring Weight

A simple idea: The difference gravity makes

Before we get into details of weight measurement, it is important to understand the two terms mass and weight, which are often interchangeably used, although they mean two different things. The mass of an object is a measure of the actual material contained in it. The weight, on the other hand, is an indicator of the force exerted by the earth's gravitational force. The confusion arises because the unit of measurement of both mass and weight is gram or kilogram. 

Let us understand this difference more easily taking the example of the earth and the moon. We do know that the earth's gravitational pull is about six times stronger than that on the moon. As a result, a person weighing 60 kgs on earth would weigh only ten kgs on the moon! The mass of the person of weight 60 kgs would be around six kgs because the gravitational constant is about 10 kg m/s2
 

Units of weight

The metric units of weight measurement are similar to those for length. We have the following units of weight measurement:

Milligram
Centigram
Gram
Kilogram
Metric Ton

Do you how much a blue whale weigh? It tips the scales at more than 200 tons. The lightest mobile phone in the world weighs a mere 40 grams. There are subatomic particles which are not even visible to the human eye, so you can imagine how light they are. Here is a small graphic that shows which units should be used for weighing different items.

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Conversion of Units

We spoke about the different units used to describe different weights. But it is not enough to know what the units are, and we also need to know how to convert one unit to the other. A candy bar might weigh just a few grams, but a whole carton of candy bars might need to have its weight described in kilograms. I could describe the weight of a mini truck in kilograms, but it would be more convenient to express its weight in tons. So, it is important to be aware of how to convert any of these units to the other.

So here are the rules for converting all the metric units of weight, and we will start from the bigger to the smaller units.

1 tonne = 1000 kilograms
1 kilogram = 1000 grams
1gram = 100 centigrams
1 centigram = 10 milligram

So, if you need to convert 1.25 tons to smaller units, this is how the calculation would be done:

1.25 tons = (1.25 x 1000) kilograms = 1250 kilograms
1250 kilograms = 1250000 gram

What about the other way round? Say you want to convert 57 milligrams into bigger units? This is how the calculation would look like:

\(\begin{align}   & 57{\text{ milligrams}} = \left( {\frac{{57}}{{10}}} \right){\text{ centigrams}} = 5.7{\text{ centigrams}}\\    & 5.7{\text{ centigrams}} = \left( {\frac{{5.7}}{{100}}} \right){\text{ grams}} = 0.057{\text{ grams}}\\    & 0.057{\text{ grams}} = \left( {\frac{{0.057}}{{1000}}} \right){\text{ kilograms}} = 0.000057{\text{ kilograms}}    \end{align}\)

As you can imagine, further conversion to tons would give an impossibly small number, so we are letting it go since you get the drift, don't you?

Some alternative units

We only spoke about the SI units of weight measurement here, but in some special circumstances, some older units of weight are also used, like ounces and pounds. 1 pound is equal to 16 ounces. 1 kilogram is equal to 2.20 pounds, and 1 ounce is 28.35 grams. Keeping these basic conversions in mind is useful.

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