Earth's attraction on an object is the weight of that object. The force of the earth's weight depends on the value of the gravitational acceleration g. And weight is the product of mass (m) and gravitational acceleration (g). ie mg. If there is no gravitational force on an object, the object will be weightless.

Variation of weight in space

Such an event can only occur at infinite distances or at the center of the Earth, where g has a value of 0 (because mass m multiplied by zero is zero). Or between the Earth and the Moon or another planet, where the Earth's gravitational force on an object is neutralized by the Moon's or another planet's gravitational force.

The value of g at the surface is fixed. As a result, the weight of a person is also fixed. Nevertheless, a person on the surface can feel the difference in weight. You can also consider yourself weightless. In fact, weight and feeling weight are not the same thing. Earth's attraction force will be on a person on Earth. As a result it will also have weight. But he will feel that weight only when a reaction force equal and opposite to his weight is applied to him.

When we stand on something, such as the floor or a table, we exert a downward force equal to our own weight on the floor or table. As a result, the floor or table also exerts a force equal and opposite to the weight on us according to Newton's third law. We feel that force. More precisely, we feel weight.

Similarly, when we hang from the branch of a tree or from the cornice of a house or roof, we exert a downward force equal to our own weight on it. According to Newton's third law it also exerts an upward force on us equal and opposite to our weight.

As a result we feel weight. Now if that floor or support exerts less or more force on us than our weight, then we will feel a correspondingly less or more force than our weight. That is, we will feel ourselves to be light or heavy. And if there is no force acting against our weight, we feel weightless.

This happens when we accidentally free fall from a roof or a tree. Jumping from a diving board into a swimming pool is also free falling. Because we don't apply force to any floor or support while falling down. As a result, no floor or support exerts a force against our weight. As a result we experience weightlessness.

Again in the elevator we feel the weight change. Standing in a stationary elevator, we exert a force mg equal to our weight on the floor of the elevator. The elevator also exerts a reaction force on us equal and opposite to the weight. As a result we feel the existence of our own weight. But if the elevator is going up, then the upward movement from the stationary position causes an upward acceleration a of the elevator.

So our acceleration with respect to the elevator is (g + a). For this extra acceleration we apply a force m (g + a) greater than our own weight on the elevator. Then the reaction force that the elevator exerts on us in the opposite direction is greater than our weight mg. This is why we feel heavy.

But after that, when the elevator starts moving upwards with equal momentum, it has no acceleration. As a result, we no longer feel more force than weight. I only feel the weight. But when the elevator starts to descend, the acceleration a from the rest position is created and our acceleration relative to the elevator is (ga).

With this low acceleration we exert a force m (ga) less than our own weight on the elevator. As a result, the lift also exerts less force on us than the weight in the opposite direction. So we feel light. Meaning, we feel underweight.

If the elevator is falling freely, i.e. if the elevator also has acceleration g, then our acceleration relative to the elevator will be (gg). That is, zero. Therefore we will not apply any force on the elevator. Then the elevators will not exert any reaction force on themselves against our weight.

Then we will feel weightless. Of course, this will happen if the elevator rope breaks and falls down under the influence of gravity. Or if an elevator from a great height descends with an acceleration equal to the acceleration of gravity. In this case, if a spring is suspended from the roof of the elevator, the cut point of the spring will be at zero. That is, the weight of the object will show zero.

And if the elevator descends with an acceleration (a) greater than g, then the downward acceleration of the elevator relative to our position will be (ag). As a result, the floor of the elevator will move downwards with an acceleration of (ag) from our feet. In this state we will continue to float in the void. And our heads will hit the roof of the elevator shortly after.

There is no difference between a spaceship orbiting the Earth or the Moon, and an elevator falling freely down. Astronauts orbit the Earth in circular orbits at a fixed altitude. For this circular motion, the acceleration of the spacecraft is towards the center of the Earth. And its value is equal to the value of g at that height.

In this case the acceleration of the astronaut relative to the walls of the spacecraft is (gg) = 0. Since the astronaut exerts no force on the floor of the spacecraft, he experiences no reaction force against his weight. Astronauts experience weightlessness as a result.

In this condition, if an object is released from the spacecraft, it does not fall down. Even if a glass filled with water is turned upside down, water will not fall. Because everything will feel weightless. But nothing is really weightless. Because the astronaut has mass in that position too. There is also a gravitational acceleration g.

So the Earth has gravity, hence weight. As for the International Space Station, the acceleration there is called microgravity. Because there the value of gravitational acceleration is close to zero. That's why water floats there, astronauts float.

Only apparent weightlessness occurs when a spacecraft accelerates to g. If the spacecraft is not orbiting the Earth in a circular path or standing still rather than free-falling toward the Earth, the astronauts will definitely feel the weight.