Final answer:
The minimum grade for a ditch depends on its purpose and is typically measured in terms of the angle of the incline or slope.
Step-by-step explanation:
In Physics, the term 'grade' is typically used to refer to the angle of an incline or slope. In the case of a ditch, the minimum grade would depend on its purpose. If the ditch is designed to allow water drainage, it should have a minimum grade of at least 0.5% or 0.5 feet of fall per 100 feet of horizontal distance.
This helps ensure proper water flow and prevents stagnation. However, if the ditch is meant for other purposes such as irrigation or navigation, the minimum grade may vary depending on the specific requirements.