Question

How they can reach zero gravity in a plane (when astronauts are practicing)?

A person in a falling elevator experiences the feeling of 'zero g' because the elevator is accelerating downward at the same rate as its passenger. Both fall with a velocity increasing at a rate of 32 ft/sec (9.8 m/s) every second near the surface of the Earth. Any experiment within the confines of the elevator will replicate an environment outside of any gravitational field (until the elevator hits bottom!).

In a 'vomit comet' airplane ride, the aircraft replicates a falling elevator in its vertical motion. Combined with its forward motion, it actually follows a parabolic trajectory to simulate a weightless environment until the approaching ground enforces a return to level flight.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

If the plane 'falls' so that it is falling the same rate as the people inside, then 'weightlessness' will result. Actually, planes fly in a parabola to make this trick happen. If you toss a rock through the air (other than straight up), it follows a path called a parabola--and the plane deliberately follows the same path. Eventually the plane has to pull out of the parabola, or it will hit the earth! The plane repeats this maneuver over and over to give the astronauts practice floating and doing some quick procedures.
Answered by: Keith Tipton, BA, physics, Rice U.

The plane the astronauts practice in is not actually without gravity. After all you know that gravity is everywhere and we are always under the influence of gravity. This airplane is in free fall which means that it is simply falling straight down! Since the astronauts are falling too their perception is that they are floating. That seems strange doesn't it! But think about it: The astronauts and the plane are falling at the same rate so if the windows are blocked and the astronauts cannot see outside, i.e. they cannot see the ground coming up to them at a hundred miles an hour, they feel like they are floating. If you could see them you would say that they are not floating at all; you would say they were falling, falling with the plane.

The misconception about weight is that we think of weight as pushing down. We think we have weight because we push down on the earth, or we push down on a scale. But this does not give us weight! We have weight only because something else pushes back up! The earth pushes up on us so we are stopped from falling. If you were to stand over a hole there would be no earth pushing up on you and you would fall but during the fall you would be weightless because there was nothing pushing up on you. So you fall because of gravity and you are weightless because nothing is pushing you up.
Answered by: Tom Young, Science Teacher, Whitehouse High School

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