The study of sound is called sonics and the study of sound waves are acoustics
Answer: 
Explanation:
A direct proportionality means a linear relationship between two variables and rate of change means an application of derivatives. Hence, the mathematical model is:

The actual size of the Solar system is too big to show without making a much smaller model. If someone wants to see the orientation of the planets a model has to be made so we can see it without flying out too space.