Space bodies, including Earth, are not stationary because of several factors, the most significant of which is the influence of gravity and the principles of motion.
Gravity: Gravity is the force of attraction between objects with mass. All objects with mass exert gravitational forces on each other, causing them to be pulled toward one another. In the case of celestial bodies like Earth, the gravitational force exerted by the Sun, the Moon, other planets, and even nearby asteroids or comets affects their motion. This gravitational interaction results in orbits, rotations, and other movements.
Orbital Motion: Objects in space, such as planets, moons, and satellites, often move in orbits around larger bodies. These orbits are the result of a balance between the gravitational pull of the central body and the object's velocity. In the case of Earth, it orbits the Sun, and the Moon orbits Earth. These orbital motions are governed by the laws of celestial mechanics, such as Kepler's laws, which describe the shape, size, and duration of orbits.
Rotational Motion: Many space bodies, including Earth, rotate or spin on their axes. This rotational motion contributes to day and night cycles and the shaping of their physical features. The rotation of Earth on its axis, for example, gives rise to the alternation between day and night.
Interactions and Perturbations: Space is a dynamic environment where numerous objects interact with each other. These interactions can cause perturbations or disturbances in the motion of space bodies. For instance, the gravitational pull of the Moon and the Sun creates tidal forces that affect Earth's rotation and cause ocean tides. Additionally, gravitational interactions with other planets or asteroids can cause slight changes in the orbits of celestial bodies over time.
In summary, the motion of space bodies, including Earth, is influenced by gravity, resulting in orbital and rotational motion. These bodies are not stationary because they are subject to gravitational forces exerted by other objects in space. The combination of gravitational interactions and the principles of motion shapes the dynamic nature of celestial bodies and their movements.