Define length. Give its various units.

1. Length is defined as the straight line distance between two points.
2. Its SI unit is metre.
3. Metre is denoted by the symbol m.

Other units of length:

1. Different objects have different lengths.
2. So we have different units to measure length.
3. Sometimes we need to measure a very large distance and sometimes a very short distance.
4. Accordingly, we choose the unit to measure the length.
5. Other units are:

1. Millimetre (mm)
2. Centimetre (cm)
3. Decimetre (dm)
4. Metre (m)
5. Kilometre (km)
6. Inch (inch)
7. Foot (ft)
8. Yard (yd)
9. Astronomical unit (AU)