The feeling that the Earth is not rotating, despite moving at an incredible speed of about 1,600 kilometers per hour at the Equator, is due to a few reasons:

1. **Constant Motion**: The Earth is rotating steadily and smoothly. Just like when you are in a car that is constantly moving and you don't feel the motion unless there is a sudden change, the Earth's rotational motion is gentle enough that it can't be felt directly.

2. **Inertial frame of reference**: Our body and everything around us are in motion along with the Earth. Therefore, there is no external reference point that allows us to feel the rotational movement.

3. **Gravity**: We are subject to the Earth's gravity, which keeps us firmly attached to its surface. Gravity is a force that acts uniformly in all directions, which also contributes to the feeling that we are at rest relative to the Earth.

4. **Brain Adaptation**: Our brains are incredibly adaptable and can filter out constant sensory input to focus on what is relevant to our survival. Since the Earth’s rotation is constant and poses no immediate threat, our brains simply ignore this movement.

So even though the Earth is spinning at an impressive speed, we don't feel this movement due to a combination of physical and psychological factors.

Why don't we notice the relative motion in the Earth's rotation?

We do not perceive relative motion in the Earth's rotation mainly because of two factors: the smoothness of the motion and the lack of an external reference point.

1. **Smoothness of motion**: The Earth's rotation is a smooth and constant motion. Just as when we are inside a vehicle in constant motion and we do not feel the sensation of movement unless there is a sudden change, the Earth's rotation is so smooth that our body does not perceive it directly. There are no sudden accelerations or decelerations that we normally perceive.

2. **Lack of external reference point**: We are all moving along with the Earth. There is no external reference point close enough to give us a sense of motion. For example, when we are in an airplane, we can feel the motion relative to the ground because the ground is far enough away to serve as an external reference point. However, there is no similar reference point on the scale of the Earth that would allow us to feel its rotational motion.

Furthermore, our perception of motion is influenced by brain adaptation and gravity. Our brains are adaptable and tend to filter out constant sensory stimuli, such as the Earth’s rotation, especially when they do not pose an immediate threat. Furthermore, gravity keeps us firmly attached to the Earth’s surface, which contributes to the feeling of stability and stillness, even when the planet is moving.

The role of gravity in the rotation of the planet

Gravity plays a crucial role in Earth's rotation, influencing its structure, movement, and even its shape. Here are some important aspects of gravity's role in the planet's rotation:

1. **Planet Formation**: During the formation of Earth and other celestial bodies, gravity plays a key role in agglomerating materials to form spherical structures. As materials accumulate, gravity pulls them toward the center, forming a sphere. This is known as hydrostatic equilibrium, and it is essential for the formation of a rotating celestial body.

2. **Angular momentum**: Gravity affects the Earth's angular momentum. Angular momentum is a measure of the amount of rotation of an object around an axis. The Earth has significant angular momentum due to its rotation, and gravity acts to maintain this angular momentum, influencing the speed and direction of the planet's rotation.

3. **Torsion of the rotation axis**: The gravity exerted by the Moon and the Sun exerts a significant influence on the torsion of the Earth's rotation axis. This results in the movements of precession and nutation, which are slow, cyclical variations in the orientation of the Earth's rotation axis over time. These movements are influenced by the uneven distribution of mass around the equator and by the gravitational forces exerted by other celestial bodies.

4. **Rotation Stabilization**: Gravity also plays a role in stabilizing the Earth's rotation. The planet's spherical shape and the distribution of its mass help balance gravitational forces over time, keeping the Earth in a relatively stable state of rotation.

In summary, gravity is fundamental to the formation, stability and movement of the Earth, including its rotation. It influences the shape of the planet, the angular momentum, the twisting of the rotation axis and the stabilization of the rotation over time.