Why don’t we observe the Earth moving towards an apple when it falls?

We don’t observe the Earth moving towards an apple when it falls primarily due to the significant disparity in mass between the Earth and the apple, combined with the gravitational acceleration experienced on Earth’s surface.

The Earth, with a mass of approximately 5.97 x 10 power 24 kilograms, exerts a gravitational force on the apple, which has a much smaller mass, typically around 0.1 kilograms. According to Newton’s law of universal gravitation, every mass attracts every other mass in the universe with a force that depends on the masses of the objects and the distance between them. However, the magnitude of this force is proportional to the product of the masses and inversely proportional to the square of the distance between them.

When an apple falls towards the Earth, it accelerates due to the Earth’s gravitational field, which on the Earth’s surface is approximately 9.81 meters per second squared 9.81 m/second square. This acceleration is directed towards the center of the Earth. The force exerted by the Earth on the apple causes it to accelerate downward, while the Earth’s acceleration towards the apple is so minuscule that it is effectively negligible and imperceptible.

In practical terms, the Earth’s mass is so vast compared to the apple that the resulting acceleration of the Earth towards the apple is far too small to observe or measure directly. Therefore, from our perspective on Earth’s surface, we simply observe the apple falling due to the Earth’s gravitational pull, without noticing any movement of the Earth towards the apple. This concept underscores the importance of considering relative masses and forces in gravitational interactions between objects.