Long and Short - Measuring Length

Units of Length: We measure length using different units based on the size of the object. Small objects like a pencil are measured in centimeters ($cm$), larger objects like a classroom wall are measured in meters ($m$), and very long distances like the road between two cities are measured in kilometers ($km$).

Using a Ruler: When measuring with a ruler, always start from the $0$ mark, not the edge of the ruler. Imagine a straight line segment where one end touches the $0$ mark and the other end aligns with a number on the scale; that number represents the length.

Relationship Between Units: Length units are related to each other by factors of $10, 100,$ or $1000$. A meter scale is divided into $100$ equal parts called centimeters. Similarly, a kilometer consists of $1000$ meters.

Converting Units: To convert meters to centimeters, we multiply the value by $100$. To convert kilometers to meters, we multiply by $1000$. For example, a $2\text{ m}$ long table is $2 \times 100 = 200\text{ cm}$ long.

Visualizing Distance: The shortest distance between two points, like Point A and Point B on a map, is a straight line. If you travel along a curved or zigzag path, the total length will be longer than the straight-line distance.

Comparing Lengths: To compare two different lengths, we must first convert them to the same unit. If a ribbon is $3\text{ m}$ long and a string is $250\text{ cm}$ long, we convert $3\text{ m}$ to $300\text{ cm}$ to see that the ribbon is longer.

Estimation: Estimating helps us guess the approximate length before measuring. For instance, a standard door is about $2\text{ m}$ high, and a typical Grade 4 student's height is usually between $120\text{ cm}$ and $140\text{ cm}$.