A fin is a surface used to produce thrust by travelling in water or another liquid media. The fist use of the word was for the limbs of fish, but has been extended to include or other animal limbs and man made devices.
The foremost use of fins are to propel an object through lateral thrust (see mechanics).
Examples of fin use:
- Propellers usually have a number of fins that work to translate tourquing force to lateral thrust, thus propelling a ship.