Your taking a walk in a warm fall morning the temperature is about 70 degrees Fahrenheit and you cannot see a cloud anywhere in the sky you notice that the ground has no dew on it either this means

The relative humidity is low

Explanation:

The higher the dew point rises, the greater the amount of moisture in the air. The lower the humidity, the lower the dew point. The dew point is low and thus water cannot exist in liquid state but as a gas.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

in the analysis of systems that involve fluid flow, we frequently encounter the combination of properties u and pv.