Final answer:
The Moon is in a stable orbit around Earth due to a balance of gravitational pull and its sideways motion. It doesn't fall into the Earth because of its inertia and the orbit around a common center of gravity with Earth. Newton's third law explains the mutual forces between Earth and the Moon that also contribute to this balance.
Step-by-step explanation:
If the moon is in free-fall, why doesn't it fall into the Earth? The concept of free-fall might imply that the Moon should be pulled directly towards the Earth and crash into it, but in reality, the Moon is also moving sideways at a high speed. This sideways motion creates a balance between the gravitational pull of the Earth and the Moon's inertia, which is a tendency of an object to stay in motion unless acted upon by another force. This state of motion follows Newton's laws and the law of universal gravitation.
Now, considering the Earth and Moon together, the system does not remain stationary. According to Newton's third law of motion, the Earth exerts a gravitational force on the Moon, and in return, the Moon exerts an equal and opposite force on the Earth. However, since we are on Earth, we move with it and do not directly sense this interaction. Nevertheless, the effects are observable, such as in the tides created by the Moon's gravitational influence on Earth.
Moreover, both Earth and the Moon, rather than each individually, orbit around their common center of gravity. The actual point of this orbit lies inside the Earth but not at its exact center. This creates a motion where the Earth also moves slightly in a small orbit as the Moon orbits it, which is why Earth is not stationary in the system.
Regarding the Moon's orbit around the Sun, the Moon is indeed affected by the gravitational fields of both the Earth and the Sun. These forces do not always add up but can sometimes be opposite depending on the positions of the Earth, Moon, and Sun in their orbits.