Distinguished between soft and hard magnetic material

Waves that cause the most damage during an earthquake are a. surface waves c. s waves b. p waves d. ocean waves

What is the single most important equation in all of physics?

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?