Long and Short - Conversion of Units

Length is the measurement of how long an object is or the distance between two points. Visualize a straight line stretching from a starting point A to an ending point B to represent this distance.

Standard units of length include Millimetres ($mm$), Centimetres ($cm$), Metres ($m$), and Kilometres ($km$). On a standard 15 cm ruler, the tiny subdivisions between numbers are $mm$, and the numbered marks are $cm$.

Centimetres ($cm$) are used for measuring small objects like a pencil or a notebook. Imagine your fingernail width is roughly $1\text{ cm}$.

Metres ($m$) are used for medium lengths like the height of a door or the length of a playground. Imagine a large step taken by an adult is approximately $1\text{ m}$ long.

Kilometres ($km$) are used for measuring very long distances, such as the distance between your home and school. Imagine a long road where 1000 metre-long sticks are placed end-to-end to cover $1\text{ km}$.

To convert from a larger unit to a smaller unit (e.g., $m$ to $cm$), we multiply. Visualize a 'Conversion Staircase' where you multiply by 100 when jumping down from Metres to Centimetres.

To convert from a smaller unit to a larger unit (e.g., $cm$ to $m$), we divide. Visualize moving up the 'Conversion Staircase' where you divide by 100 to group small centimetres into larger metre units.

When adding or subtracting lengths with different units, always convert them to the same unit first. For example, to add $2\text{ m}$ and $50\text{ cm}$, convert the metres to centimetres so you are adding $200\text{ cm} + 50\text{ cm}$.