Long and Short - Estimation of Length

Length is a measure of how long an object is from one end to the other. Imagine a straight line connecting the two furthest points of an object; that path represents its length.

Non-standard units like handspan, cubit, or pace were used in ancient times. A handspan is the distance from the tip of the thumb to the tip of the little finger when the hand is spread out. However, these are not accurate because everyone's hand size is different.

The Centimeter ($cm$) is a standard unit used for measuring small objects like pencils, erasers, or notebooks. On a standard $15 \text{ cm}$ ruler, you will see small marks numbered $0$ to $15$; the distance between any two consecutive numbers is $1 \text{ cm}$.

The Meter ($m$) is used for measuring longer things like the length of a room, the height of a tree, or the length of a cloth. It is a larger unit than the centimeter, where $1 \text{ m}$ is exactly the same as $100 \text{ cm}$.

The Kilometer ($km$) is used to measure very long distances, such as the distance between two cities or the length of a long river. Think of it as $1000$ meter sticks placed end-to-end.

When using a ruler, always align the start of the object with the $0$ mark. If you start at the edge of the ruler instead of $0$, your measurement will be wrong. The number at which the object ends tells you its length.

Estimation is making a 'smart guess' about the length of an object before measuring it. For example, if you know your finger is about $1 \text{ cm}$ wide, you can estimate a book's width by seeing how many fingers fit across it.

Comparing lengths involves looking at two or more objects to see which is 'longer' and which is 'shorter'. If Object A reaches further than Object B when placed side-by-side starting at the same point, Object A is longer.