In the context of space, the term "vacuum" refers to the absence of matter and particles, rather than the absence of any physical forces. Even in a vacuum, objects can still move due to various factors:
Inertia: An object in motion tends to stay in motion unless acted upon by an external force, as described by Newton's first law of motion. Once an object is set in motion, it will continue moving until another force acts upon it to change its velocity or trajectory.
Propulsion: Objects can be propelled through space by applying a force to them. For example, spacecraft use engines to generate thrust, expelling gases or accelerating particles to create a reaction that propels the spacecraft forward. This principle is governed by Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.
Gravitational Forces: Objects in space are subject to the gravitational forces exerted by other celestial bodies. Planets, stars, and other massive objects create gravitational fields that can influence the motion of nearby objects. By exploiting the gravitational forces of celestial bodies, spacecraft can use gravitational assists or slingshot maneuvers to gain speed or change their trajectory.
It's important to note that even though space is a vacuum devoid of air or other atmospheric resistance, objects can still experience the effects of gravity and other forces, allowing for motion and movement.