You might be most familiar with sonography's role in the field of obstetrics to produce an ultrasound image of an unborn baby. Sonography is also used to analyze tissues and organs of the body, such as the heart, eyes and abdomen.
Etymology: Pierre S. de Laplace, French physicist, 1749-1827. a principle of physics that the tension on the wall of a sphere is the product of the pressure times the radius of the chamber and the tension is inversely related to the thickness of the wall.
The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit. This is one of Kepler's laws.This law arises from the law of gravitation. Newton first formulated the law of gravitation from Kepler's 3rd law. Kepler's Law of Periods in the above form is an approximation that serves well for the orbits of the planets because the Sun's mass is so dominant.