Measurement - Measurement of Weight

Weight, often called Mass in mathematics, measures how heavy an object is. In the ICSE Grade 4 curriculum, we focus on three main units: Milligrams ($mg$), Grams ($g$), and Kilograms ($kg$). Imagine a tiny grain of salt weighing a few $mg$, a single grape weighing about $5$ $g$, and a large pumpkin weighing $5$ $kg$.

The Kilogram ($kg$) is the standard unit of weight used for heavier objects like suitcases, human body weight, or sacks of flour. A common visual for $1$ $kg$ is a standard liter bottle of water or a large bag of sugar.

The Gram ($g$) is used for lighter objects. You can visualize $1$ $g$ as the weight of a small metal paperclip or a single plastic pen cap. There are exactly $1000$ grams in one kilogram, which makes the gram a 'sub-multiple' of the kilogram.

The Milligram ($mg$) is the smallest unit we study, used for very light items like feathers, flower petals, or the dosage of medicine in a tablet. Visually, $1000$ milligrams are packed into just $1$ single gram.

To convert from a larger unit to a smaller unit, we use multiplication. When moving 'down' the unit scale from $kg$ to $g$, we multiply by $1000$. For example, $2$ $kg$ becomes $2 \times 1000 = 2000$ $g$. You can visualize this as 'expanding' the number as you move to a smaller, more precise unit.

To convert from a smaller unit to a larger unit, we use division. When moving 'up' the scale from $g$ to $kg$, we divide the value by $1000$. For instance, $5000$ $g$ becomes $5000 \div 1000 = 5$ $kg$. If a number is not a perfect multiple of $1000$, the remainder stays in the smaller unit (e.g., $4500$ $g$ is $4$ $kg$ and $500$ $g$).

We use different types of balances to measure weight. A manual Beam Balance uses two pans; one pan holds the object and the other holds standard metal weights. When the horizontal beam is perfectly straight, the weights are equal. Modern Electronic Balances show the weight as a digital number on a screen for higher precision.