How can the Earth move in the absence of external forces??

The Earth, being in a circular motion around the Sun, is continuously changing its velocity, or speed in a particular direction, because the direction of travel is changing. This means that the Earth is not only moving, but also accelerating. In other words, forces cause acceleration.

The point is that while there is evidence of Earth's motion—days, seasons, planet phases, etc.—it is the alteration in Earth's motion that indicates the application of force.

The conservation of energy and momentum—momentum can be linear, angular, or both—are the two basic laws of physics.

An external force, such as a collision, is the only way to alter an object's momentum and energy.

The conservation of angular momentum allows the Earth to continue rotating in multiple directions, as it does in its 24-hour orbit.

A little more explanation is needed for the Earth's orbit. An object moving in an ellipse or circle needs an inward centripetal force to continuously change its velocity.

Newton was never satisfied with how gravity worked, but he used it to explain this.

As demonstrated by Einstein, momentum and energy cause four-dimensional spacetime to curve, and this curvature results in gravity.

Spacetime is curved by the mass of the Sun. In curved spacetime, the Earth moves along a geodesic, which is an ellipse in three dimensions and the four-dimensional equivalent of a straight line.

According to Newton's first law of motion, an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. In the case of the Earth, there are several factors that allow it to move in the absence of external forces:

1. Inertia: The Earth has inertia, which is the tendency of an object to resist changes in its motion. Due to its mass, the Earth continues to move in its orbit around the Sun without the need for additional forces to maintain its motion.

2. Gravitational force: The gravitational force between the Earth and the Sun keeps the Earth in its orbit. This force acts as the centripetal force, pulling the Earth towards the Sun and preventing it from moving in a straight line.

3. Conservation of momentum: The Earth's motion is also governed by the principle of conservation of momentum. As long as there are no external forces acting on the Earth-Sun system, the total momentum of the system remains constant. Therefore, the Earth continues to move in its orbit without the need for additional forces.

In summary, the Earth can move in the absence of external forces due to its inertia, the gravitational force exerted by the Sun, and the conservation of momentum.