In order to attain a secure, stable state of weightlessness, we would have to escape the effect of gravity in the second way: with the aid of inertial forces.
Figure 5. Circular free orbiting of an object around the Earth. The object's weight is offset by the centrifugal force generated during the orbiting. The object is, therefore, in a stable state of free suspension in relation to the Earth.
Key: 1. Centrifugal force; 2. Orbiting object; 3. Weight; 4. Are opposite and equal to one another; 5. Earth; 6. Circular free orbit
This is attained when the attracting celestial body, for example, the Earth, is orbiting in a free orbit at a corresponding velocity (gravitational motion). The centrifugal force occurring during the orbit and always directed outward maintains equilibrium with the attractive forceindeed, it is the only force when the motion is circular (Figure 5)or simultaneously with other inertial forces occurring when the orbit has another form (ellipse, hyperbola, parabola, Figure 6).
Figure 6. Various free orbits around a celestial body. In accordance with the laws of gravitational movement, a focal point of the orbit (the center in the case of a circle) must always coincide with the center of mass (center of gravitaty) of the orbiting celestial body.
Key: 1. Parabolic orbit; 2. Hyperbolic orbit; 3. Celestial body; 4. Elliptical orbit; 5. Circular orbit
All Moon and planet movements occur in a similar fashion. Because, by way of example, our Moon continuously orbits the Earth at an average velocity of approximately 1,000 meters per second, it does not fall onto the Earth even though it is in the Earth's range of attraction, but instead is suspended freely above it. And likewise the Earth does not plunge into the sun's molten sea for the simple reason that it continuously orbits the sun at an average velocity of approximately 30,000 meters per second. As a result of the centrifugal force generated during the orbit, the effect of the sun's gravity on the Earth is offset and, therefore, we perceive nothing of its existence. Compared to the sun, we are "weightless" in a "stable state of suspension;" from a practical point of view, we have been "removed from its gravitational effect."
The shorter the distance from the attracting celestial body in which this orbiting occurs, the stronger the effect of the attractive force at that point. Because of this, the counteracting centrifugal force and consequently the orbiting velocity must be correspondingly greater (because the centrifugal force increases with the square of the orbiting velocity). While, by way of example, an orbiting velocity of only about 1,000 meters per second suffices at a distance of the Moon from the Earth, this velocity would have to attain the value of approximately 8,000 meters per second for an object that is supposed to orbit near the Earth's surface in a suspended state (Figure 7).
Figure 7. The orbiting velocity is that much greater the closer the free orbit movement occurs to the center of attraction.
Key: 1. Moon; 2. Approximately 1,000 meters per second; 3. Approximately 8,000 meters per second; 4. Earth
In order to impart this velocity to an object, that is, to bring it into a stable state of suspension in relation to the Earth in such a manner, and as a result to free it from the Earth's gravity, an amount of work of about 3,200 metertons per kilogram of weight is required.