I want to ask why does a person feel weightless during free fall? Please give a specific and clear answer, without making it complex.
It is a result of how we feel weight.
Stand up. What is happening to you at the moment is that the ground is exerting an upward force on your feet. The planet below you is exerting a downward force on the hamburger in your stomach. This causes compression in your knees which is sensed by nerves in your knees.
Now put yourself into free fall. Good. What is happening now is that your feet, knees and hamburger are all being accelerated together in the same direction so that there is no resultant compression in your knees that the nerves there can sense.
"Weightlessness" occurs when there is no support on your body. When your body is effectively in "free fall", accelerating downward at the acceleration of gravity, then you are not being supported.
The perception of apparent weight comes from the support that you feel from the floor, from the seat in a bus or plane. Different sensations of apparent weight can occur on a roller-coaster or in an aircraft because they can accelerate either upward or downward.
In other words, turn your question around and ask yourself, why do I feel weight when I walk across the floor? It's because of the the support force the floor gives you.