Why does an apple from an apple tree falls on earth but not on the moon?

Relative motion:

1. Physics laws that apply while you are at rest on the earth also apply when you are in any reference frame that is traveling at a constant velocity with regard to the earth.
2. For example, if the motion is in a straight line with constant speed, you may toss and catch a ball in a moving bus.
3. The motion may look different when seen from a different reference frame, but this may be explained by mentioning the reference frame's relative velocity in the motion description.

Relative motion between Earth and apple:

1. Moreover, according to the first law of motion, $F=ma$. Here, $F$ is force, $m$ is mass and $a$ is acceleration of the object.
2. The earth and apple pull each other with the same gravitational force.
3. Since the size of the apple is very small as compared to the earth, the apple will gain enough acceleration to fall on it whereas the earth will not move towards the apple due to its large size and very small acceleration produced on it due to the apple.
4. Thus, the earth does not move towards the apple.

Relative motion between Earth and Moon:

1. In space, there is a relative motion between Earth and the moon.
2. The moon never truly hits the earth's surface.
3. To comprehend this, we must first comprehend the nature of the force between the moon and the earth, as well as the movement of the moon under this force.
4. The gravitational force operates between the earth and the moon, and the moon moves in a circular orbit owing to the centripetal force caused by the gravitational force.
5. Similarly, the earth and sun have gravitational attraction between them.
6. So, while the moon does descend towards the earth, the earth also travels in its orbit, covering more space away from the moon than the moon does.
7. As a result, the moon never falls on the earth.
8. Moreover, the size of the moon is very large in comparison to the apple so the acceleration of the moon toward earth is negligible according to $F=ma$.

Thus, an apple falls on the earth but not the moon.