In this paper, we introduce generalized entropy, acceleration of its entropy and its partial entropy. We assume that generalized entropy can be represented as a second-order polynomial by applying the idea of logistics function to its entropy. Besides, we show that the inverse of partial entropy can represent Newton's gravity, which is an inverse square law. By applying these concepts, we attempt to explain that 1) gravity become constant within small distance with some conditions. It is possible that gravity have 5-states within small enough distance. There exists possible anti-force, which is the opposite of Newton's gravity among 5-states. Furthermore, within small distance, we show the possibility that gravitational potential and Coulomb potential can be treated in the same way, that 2) the rotation speed of the galaxy does not depend on its radius if the radius is within the size level of the universe. (The galaxy rotation curve problem), and that 3) gravitational acceleration toward the center may change at long distance compared to Newton's gravity. We show that it become an expansion of Newton's gravity, and that the possibility of the existence of some constants which controls gravity and the speed of galaxies, and that gravity may relate on entropy. It also describe the relationship between Yukawa-type potential and negative partial entropy. Using equations proposed in this paper, it attempt to compare the ratios of size of the fundamental 4-forces in nature (strong force, electromagnetic force, weak force and gravity). Furthermore, it suggests that there may exists new forces, and that gravitational constant $G$ can fluctuate if entropy changes. Thermodynamics, quantum, gravity, electromagnetic and ecology may be unified through entropy.