The reason Earth doesn't collide with other planets when they pass near us in their orbits around the Sun is primarily due to the vastness of space and the relatively small sizes of the planets compared to the distances between them.
While the planets in our solar system do orbit the Sun, their orbits are not perfectly circular but rather slightly elliptical. This means that their paths around the Sun are slightly elongated and inclined relative to each other. As a result, there are times when the orbits of different planets bring them relatively close to each other.
However, even during these close approaches, the distances between planets are immense. The average distance between Earth and Mars, for example, is about 225 million kilometers (140 million miles). The distances between Earth and the other planets are even greater. These vast distances ensure that the likelihood of collisions is extremely low.
Additionally, the orbits of planets are governed by the laws of celestial mechanics, particularly Newton's laws of motion and the law of universal gravitation. These laws describe the gravitational interactions between celestial bodies and help maintain the stability of their orbits. The gravitational force between planets acts as a dominant force, keeping them in their respective paths around the Sun and preventing collisions.
In summary, the combination of the immense distances between planets and the gravitational forces that govern their motions ensures that collisions between planets in our solar system are highly unlikely.