A central force is a type of force that acts between two objects, where the force is always directed towards a fixed point, known as the center of force. In elliptic and parabolic orbits, the center of force is typically the focus of the ellipse or parabola, respectively.
An object follows an elliptic or parabolic orbit due to the influence of a central force, which is typically caused by the gravitational force between two objects. The shape of the orbit depends on the strength and direction of the force, as well as the initial velocity of the object.
Elliptic orbits are closed and periodic, meaning that the object will return to its starting point after a certain amount of time. Parabolic orbits are open and non-periodic, meaning that the object will not return to its starting point. Additionally, the eccentricity of an elliptic orbit is always less than 1, while the eccentricity of a parabolic orbit is exactly 1.
The period of an object in an elliptic or parabolic orbit can be calculated using Kepler's Third Law, which states that the square of the orbital period is proportional to the cube of the semi-major axis of the orbit. For a parabolic orbit, the semi-major axis is infinite, resulting in an infinite orbital period.
Yes, a central force in an elliptic or parabolic orbit can change over time. This can be due to the influence of other forces, such as the gravitational pull of other objects, or due to changes in the distance between the two objects. These changes can cause the shape and/or period of the orbit to change as well.