Weightlessness is defined as the complete or near-complete absence of the sensation of weight. It is the state in which the apparent gravity effect is zero. This is also termed zero-G, and it occurs in the absence of any contact force is not the absence of gravity as it is commonly perceived but just the experience of feeling weightless upon objects including the human body. Generally Bodies undergoing free fall and those in orbit experience this situation. For example, man-made satellites in orbit around the earth all experience zero gravity when they are on board.
Weightlessness or Zero Gravity
Weight is a measurement of the force on an object at rest in a relatively strong gravitational field (such as on the surface of the Earth). The sensation of weight originates from contact with supporting floors. The sensation of weight can also be produced, even when there is zero gravitational field, and when contact forces act upon and it overcomes a body's inertia by mechanical, non-gravitational forces- such within an accelerating vehicle or in a centrifuge a rotating space station.
Now, remember when you have ever gone bungee jumping or cliff diving? Roller coaster? Drop tower ride where you are just free-falling for a while? It seems as if we are weightless for a while? Thus, we can conclude from this that our weight is defined as long as we have something supporting us to realize our weight. we will feel weightlessness when there is no supporting force acting on your body.
Difference Between Zero Gravity and Microgravity or No Gravity
Zero-gravity is a state in which the effects of gravity are not felt to us or we can call it weightlessness, So what is it called when there is no gravity then? Actually, there is nothing such as the absence of gravity, even in space. For example, we know that the earth orbits the sun because of the gravitational pull of the sun, similarly the moon is also held in its orbit around the earth, and it is because of the earth’s gravity. And yet when astronauts are in space, they have experienced weightlessness and go on spacewalks. NASA defines this phenomenon as microgravity and this is the situation when gravity is everywhere, but the influence of it is so small to be considered that it can be regarded negligible.
Way to Avoid Weightlessness or Zero Gravity
The sensation Weightlessness is very much in contrast with current human experiences in which a non-uniform force is acting, such as:
While standing on the ground, sitting in a chair on the ground, etc., where gravity is countered by the support force of the ground,
When we are flying in a plane, the support force is transmitted from the lift the wings provided.
During the use of a parachute when the atmospheric drag decelerates a vehicle
In the above cases where an object doesn't feel weightlessness, it is because a force acts non-uniformly on the object in question. All these cases involve aero-dynamic lift, drag, and thrust are all non-uniform forces (they act at a point or part of the surface, rather than acting on the entire body), and thus create the phenomenon of weight. This non-uniform force is also transmitted to an object at the point of contact with a second object, such as the contact between the surface of the Earth and one's feet, or between a parachute harness and one's body avoiding the phenomenon of weightlessness.
Weightlessness or Zero Gravity in a Spacecraft
In spacecraft outside a planet’s atmosphere weightlessness is experienced when no propulsion is applied as well as the vehicle does not rotate. Weightlessness is not experienced when the spacecraft is firing its engines or when it is almost entering the atmosphere because in this situation the thrust provided by the engine acts at the surface of the nozzle of the rocket and is transmitted throughout the spacecraft and also via tensile and compressive forces to people inside it.