The Physical Behavior of Objects when Gravity is Missing


In order to be able to form a concept of the general physical conditions existing in a weightless state, the following must be noted: the force of the Earth's gravity pulling all masses down to the ground and thus ordering them according to a certain regularity is no longer active. Accordingly almost following only the laws of inertia (inertial moment), bodies are moving continually in a straight line in their momentary direction of motion as long as no resistance impedes them, and they react solely to the forces (molecular, electrical, magnetic, mass-attracting and others) acting among and inside themselves. These unusual conditions must, however, lead to the result that all bodies show a completely altered behavior and that, in accordance with this behavior, our unique actions and inactions will develop in a manner entirely different from previous ones.

Therefore, human movement can now no longer occur by "walking." The legs have lost their usual function. In the absence of the pressure of weight, friction is missing under the soles; the latter stick, therefore, considerably less to the ground than even to the smoothest patch of ice. To move, we must either pull ourselves along an area with our hands (Figure 60, z), for which purpose the walls of the space station would have to be furnished with appropriate handles (for instance, straps similar to those of street cars) (Figures 60 and 61), or push ourselves off in the direction of the destination and float towards it (Figure 60, a).

It will probably be difficult for the novice to maintain an appropriate control over his bodily forces. This, however, is necessary: since he impacts the opposite wall of the room with the full force of pushing off, too much zeal in this case can lead very easily to painful bumps. For this reason, the walls and in particular all corners and edges would have to be very well cushioned in all rooms used by human beings (Figure 60).

Figure 60. A room of the space station in which a weightless state exists and which is furnished accordingly: The walls are completely cushioned and equipped with straps. No loose object is present.

K ....... Lockable small chests for holding tools and similar items.

L ....... Openings for admitting light (reference Page 143).

O ....... Openings for ventilation (reference Page 144).

z ....... Movement of people by pulling.

a ....... Movement of people by pushing off.

Key: 1. Direction of motion.

Pushing off can also be life threatening, more specifically, when it occurs not in an enclosed room but in the open; e.g., during a stay (in the space suit, see the following) outside of the space station, because if we neglected to take appropriate precautionary measures in this case and missed our destination while pushing off, then we would continually float further without end into the deadly vacuum of outer space. The no less terrible possibility of "floating off into space" now threatens as a counterpart to the terrestrial danger of "falling into the depths." The saying "man overboard" is also valid when gravity is missing, however in another sense.

Since bodies are now no longer pressed down upon their support by their weight, it, of course, has no purpose that an item is "hung up" or "laid down" at any place, unless it would stick to its support or would be held down by magnetic or other forces. An object can now only be stored by attaching it somewhere, or better yet locking it up. Therefore, the rooms of the space station would have to be furnished with reliably lockable small chests conveniently placed on the walls (Figures 60 and 61, K).

Clothes racks, shelves and similar items, even tables, as far as they are meant to hold objects, have become useless pieces of furniture. Even chairs, benches and beds can no longer satisfy their function; humans will have to be tied to them in order not to float away from them into any corner of the room during the smallest movement. Without gravity, there is neither a "standing" nor a "sitting" or "lying." In order to work, it is, therefore, necessary to be secured to the location of the activity: for example, to the table when writing or drawing (Figure 61). To sleep, we do not have to lie down first, however; we can take a rest in any bodily position or at any location in the room.

Figure 61. Writing in the weightless state: for this purpose, we have to be secured to the tabletop, for example, by means of leather straps (G) in order to remain at the table at all (without having to hold on). A man floats in from the next room through the (in this case, round) door opening, bringing something with him.

However, despite this irregularity in the physical behavior of freely moving objects caused by the absence of gravity, the manner is actually not completely arbitrary as to how these objects now come to rest. The general law of mass attraction is valid even for the space station itself and causes all masses to be attracted toward the common center of mass; however due to the relative insignificance of the entire mass they are attracted at such an extremely slight acceleration that traveling only one meter takes hours. However, nonsecured objects will finally impact one of the walls of the room either as a result of this or of their other random movement, and either immediately remain on this wall or, if their velocity was sufficiently large, bounce back again and again among the walls of the room depending on the degree of elasticity, floating back and forth until their energy of movement is gradually expended and they also come to rest on one of the walls. Therefore, all objects freely suspended within the space station will land on the walls over time; more specifically, they will approach as close as possible to the common center of mass of the structure.

This phenomenon can extend over hours, sometimes over many days, and even a weak air draft would suffice to interfere with it and/or to tear objects away from the wall, where they are already at rest but only adhering very weakly, and to mix them all up. Consequently, there is, practically-speaking, no regularity to the type of motion of weightless masses.

The latter is especially unpleasant when objects are in one room in significant numbers. If these objects are dust particles, they can be collected and removed in a relatively easy manner by filtering the air with vacuum cleaners or similar devices. However, if they are somewhat bigger as, for example, through the careless emptying of a sack of apples into a room, then the only alternative would be trapping them by means of nets. All objects must be kept in a safe place, because the ordering power of gravity now no longer exists: matter is "unleashed."

Also, clothing materials are on strike, because they no longer "fall," even if they were made of a heavy weave. Therefore, coats, skirts, aprons and similar articles of clothing are useless. During body movements, they would lay totally irregularly in all possible directions.

The behavior of liquids is especially unique in a weightless state. As is well known, they try under normal conditions to attain the lowest possible positions, consequently obeying gravity by always clinging completely to the respective supports (to the container, to the ground, etc.). If gravity is missing, however, the individual particles of mass can obey their molecular forces unimpeded and arrange themselves according to their characteristics.

In the weightless state therefore, liquids take on an independent shape, more specifically, the simplest geometric shape of an object: that of a ball. A prerequisite for this is, however, that they are subjected to only their forces of cohesion; that is, they are not touching any object they can "moisten." It now becomes understandable why water forms drops when falling. In this state, water is weightless, according to what has been previously stated; it takes on the shape of a ball that is distorted to the form of a drop by the resistance of air.

However, if the liquid is touching an object by moistening it, then overwhelmingly strong forces of cohesion and adhesion appear. The liquid will then strive to obey these forces, spreading out as much as possible over the surface of the object and coating it with a more or less thick layer. Accordingly for example, water in only a partially filled bottle will not occupy the bottom of the bottle, but, leaving the center empty, attempts to spread out over all the walls of the container (Figure 62). On the other hand, mercury, which is not a moistening liquid, coalesces to a ball and adheres to one wall of the container, remaining suspended in the bottle (Figure 63).

Figure 62. Dispersion of water in only a partially filled bottle in the absence of gravity.

Key: 1. Water; 2. An air-filled space surrounded on all sides by water.

Figure 63. Behavior of mercury in a bottle in the absence of gravity.

Key: 1. Ball of mercury.

In both instances, the position of the body is completely immaterial. Therefore, the bottle cannot be emptied by simply tilting it, as is usually the case. To achieve this effect, the bottle must either be pulled back rapidly (accelerated backwards, Figure 64) or pushed forward in the direction of the outlet and/or then suddenly halted in an existing forward motion (slowing it down in a forward movement, also as in Figure 64), or finally swung around in a circle (Figure 65).

Figure 64. Emptying a bottle in a weightless state by pulling it back.

Key: 1. Air bubbles entering.

Figure 65. In the absence of gravity, swinging a bottle of water in a circle in order to empty it. (In reality, the escaping liquid will probably not be dispersed in such a regular fashion as the discharge curve indicates.)

Key: 1. Motion of the bottle; 2. Direction of motion of the water; 3. The escaping water now freely suspended.

The liquid will then escape out of the bottle as a result of its power of inertia (manifested in the last case as centrifugal force), while taking in air at the same time (like gurgling when emptying the bottle in the usual fashion). A prerequisite for this, however, is that the neck of the bottle is sufficiently wide and/or the motion is performed with sufficient force that this entry of air can actually take place against the simultaneous outward flow of water.

[It is interesting to note that strictly speaking the described method of emptying a bottle in the absence of gravity by pulling it back or halting it proceeds in reality as if the water is poured out by turning the bottle upside down in the presence of gravity. Of course, these are completely analogous to physical phenomena {on Earth}, if the motion of pulling back and/or halting is performed exactly at the acceleration of gravity (9.81 m/sec2 for us), because as is known in accordance with the general theory of relativity, a system engaged in accelerated or decelerated motion is completely analogous to a gravitational field of the same acceleration. In the case of the described method of emptying, it can be stated that the forces of inertial mass that are activated by pulling back or stopping of the system operate in place of the missing gravity, including the bottle and its contents.]

After escaping from the bottle, the liquid coalesces into one or more balls and will continue floating in the room and may appear similar to soap bubbles moving through the air. Finally, every floating liquid ball of this type must then impact on one of the walls of the room. If it can moisten one of those walls, then it will try to spread out over them (left portion of Figure 66).

Figure 66. In the absence of gravity, escaping water would spread out over the walls in a room whose walls are easily moistened (e.g., they are somewhat damp; diagram on the left); in a room whose wall are not easily moistened (e.g., one coated with oil), the water coalesces into balls and adheres to the walls (diagram on the right).

Key: 1. Water; 2. Room with damp walls; 3. Room with walls coated with oil.

Otherwise as a result of the push, the liquid will scatter into numerous smaller balls, somewhat similar to an impacting drop of mercury. These balls float away along the walls or perhaps occasionally freely through the room, partially coalescing again or scattering once again until their kinetic energy has finally been expended and the entire amount of liquid comes to rest, coalesced into one or more balls adhering to the walls (right portion of Figure 66). (In this regard, compare the previous statements about the phenomena in a bottle, Figures 62 and 63.)

Given this unusual behavior of the liquid, none of the typical containers, such as bottles, drinking glasses, cooking pots, jugs, sinks, etc., could be used. It would hardly be possible to fill them. However, even if, by way of example, a bath could be prepared, we would not be able to take it because in the shortest time and to our disappointment, the water would have spread out of the bathtub over the walls of the room or adhered to them as balls.

Figure 67. In the absence of gravity, the otherwise usual liquid containers are replaced by sealable flexible tubes (left diagram), rubber balloons (center diagram) or syringe-type containers (right diagram).

Key: 1. Waterproof material (skin); 2. Rubber container; 3. Stopper functioning as a spigot here.

For storing liquids, only sealable flexible tubes, rubber balloons or containers with plunger-like, adjustable bottoms, similar to syringes, would be suitable (Figure 67), because only items of this nature can be filled (Figure 68) as well as easily emptied. Containers with plunger-like, adjustable bottoms function by pressing together the sides or by advancing the plunger to force out the contents (Figure 69). In the case of elastic balloons, which are filled by expanding them, their tension alone suffices to cause the liquid to flow out when the spigot is opened (Figure 70). These types of pressure-activated containers (fitted with an appropriate mouth piece) would now have to be used for drinking in place of the otherwise typical, but now unusable drinking vessels.

Figure 68. Filling a water vessel in the weightless state.

Key: 1. Wall; 2. Water supply; 3. Container; 4. The plunger is pushed forward for the purpose of removing water; 5. Connecting tube; 6. Tubular container being filled.

Similarly, the various eating utensils, such as dishes, bowls, spoons, etc., can no longer be used. If we made a careless move, we would have to float through the room chasing after their perhaps savory contents. Eating would, therefore, be possible only in two principal ways: either by eating the food in a solid form, such as bread, or drinking it in a liquid or mushy state using the pressure activated containers described above. The cook would have to deliver the food prepared in this manner.

Figure 69. In the absence of gravity, emptying a liquid container can be accomplished in an expedient manner only by pushing out (pressing out) the contents.

In his important activity, the cook would be faced with particularly significant problems, but they can also be overcome. The cook could use, for example, sealable electrical cooking appliances, constantly rotating when in use, so that (instead of the now missing gravity) the generated centrifugal force presses the contents against the walls of the container; there would also be other possibilities. In any case, cooking would not be easy, but certainly possible, as would eating and drinking. Washing and bathing as we know them would have to be completely dropped, however! Cleaning up could only be accomplished by rubbing with damp towels, sponges or the like lathered according to need, accepting whatever success this method would achieve.

Figure 70. In the case of elastic rubber balloons filled under pressure, the contents flow out of their own accord when the spigot is opened.

Key: 1. Expanded rubber container.

The more in depth we consider the situation, the more we must recognize that in reality it would in no way be an entirely unblemished pleasure to be able to float like angels, freed from all bothersome weight; not even if this state of weightlessness were perceived as pleasant. Because, gravity not only holds us in her grip; it also forces all other objects to the ground and inhibits them from moving chaotically, without regularity, freely left to chance. It is perhaps the most important force imposing order upon our existence. Where gravity is absent, everything is in the truest sense "standing on its head," having lost its foothold.


[Previous Page] [Next Page] [Table