What if gravity disappeared? – Explica .co

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A dream. Always the same. In the imagination, with Icarus or the superheroes of the fantasy series. In real life, for boom operators, airplane pilots or astronauts. This dream, to fly, to move away from the force of gravity that binds us relentlessly to the ground, keeps us confined to the surface of the Earth. To be free from gravity, what freedom that would be!

For astronauts, this dream is almost a reality, thanks to the International Space Station.

Is Earth’s Gravity Simply Stopping Us?

To answer this question, we must take into account the fact that gravitational attraction acts on the mass of objects, whatever they are. If we see a marble falling through the air, we have to imagine that each fraction of the marble is attracted towards the center of the Earth. The gravitational force is applied to the whole of the marble, to its volume. It acts in the same way on the gases that make up the ambient air, creating the protective atmosphere. Without gravity, there is no atmosphere, and there is probably no life.

Let’s look at this from a physics point of view. The movement of any object (which we call the body) depends on the forces acting on it. Since it is imposed on any body with mass, the force of gravity is found in many, if not all, of our everyday phenomena. To eliminate this force would amount to inhibiting the phenomenon which is at the origin of it. We have already mentioned the existence of our atmosphere. The same will happen with the push of Archimedes’ theorem. Does it exist in space?

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Experiment on the interaction between electrically charged drops, during a parabolic flight. ESA, A. Le Floc’h, Author provided

Due to gravity, the pressure in a fluid (air, water) increases with depth. Therefore, if an object is submerged in water, the pressure below will be greater than the pressure above. This difference causes the object to be pushed upwards. If its density is lower than that of water, this buoyancy will cause it to rise to the surface. Fleet. In the absence of gravity, the buoyancy is over… and the objects don’t sink either! The hot air masses that rise in the colder air are finished, and with them the hot air balloons are finished, the heating with radiators is finished, the combustion (candles, fire, etc.) maintained by the renewal of the air is over. constantly heated surroundings, the boiling of water stopped letting gas bubbles escape to the surface, the ocean currents stopped, it was all over.

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All these hypotheses, and many others, are the subject of scientific experimentation. The objective is to determine the role that gravity plays in a particular phenomenon. In these experiments, scientists see gravity as one force among others that can be changed: a bit like pushing an object more or less hard.

The problem is, it’s impossible to get rid of gravity. For this reason, various means have been created to simulate their absence: sounding rockets, free-fall towers, parabolic flights, the International Space Station (ISS). In all of these experimental platforms, the goal is to “drop” the experiment, including the lab, to offset the weight of the assembly. The duration of this apparent weightlessness situation depends directly on the time during which this “fall” can be maintained: from 10 seconds in a free-fall tower, to several months in the ISS.

What experiments can be carried out in zero gravity?

Weightlessness makes it possible to study objects by making them float in the air without touching them. This is particularly suitable for cases where the object in question cannot be touched, because it is charged with electricity, for example.

Like gravity, electrical force affects the volume of bodies. For electrons, which are very light, gravity dominates. However, for larger objects, such as water droplets, this is no longer the case. Today, electrically charged droplets can be found both in industry (metal and paint aerosols) and in basic research (electrically charged droplet gases).

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In everyday life, clouds harbor water droplets charged with electricity. This electricity is the source of the rays. However, the mechanism by which the drops charge and the interactions they undergo (collisions, mergers, ruptures, etc.) are relatively little known. By carrying out experiments in zero gravity, it is possible to make the drops interact and observe their dynamics for several seconds, without touching them and without being disturbed. It is also possible to study the influence of electric charge on the size of raindrops.

In certain situations, it is useful to carry out experiments in weightlessness to demonstrate a force less important than gravity.

Weightlessness to reveal capillarity

By its action on the entire volume of bodies, gravity acts at great distances: the Earth is attracted by the Sun, which is very far away. On the contrary, the field of action of the force responsible for the spherical shape of raindrops is limited to the surface of liquids. This force is called surface tension. It only occurs at the border between two fluids: air and water, for example. We can verify its existence in certain specific situations. For example, we have to blow to produce a soap bubble. The little energy that this effort costs us is used to counter surface tension.

For most objects, gravity dominates surface tension. To reverse this trend, consider small liquid objects: water droplets for example. In this case, the surface tension is able to impose the spherical shape of the drop, even if it is placed on a table. Unfortunately, if the volume of the drop increases a little (about 10 mm³ is enough), gravity takes over and the drop flattens out, eventually turning into a puddle.

To take advantage of the effect of surface tension, several studies on weightlessness focus on soap foams. With their hundreds of bubbles, foams have a large liquid surface and maximize the effect of surface tension. Due to the effect of gravity, the liquid in the foam tends to flow and the foam dries up, eventually dying. In weightlessness, this phenomenon disappears and it is possible to study wet mosses. The characteristics (stability, mechanical resistance, etc.) of these wet foams allow a better understanding of the physico-chemistry of these particular materials. The results of this research provide useful information in many industrial fields (for example, for the development of light and resistant materials) and in basic science (flows of confined fluids).

Space exploration within 400 kilometers of Earth

By trying to hide the action of gravity, research in microgravity and weightlessness makes the conquest of space a means and not an end. It complements programs aimed at understanding the vastness of the universe, and offers the possibility of approaching manned flights with a better understanding of the environment in which astronauts will immerse themselves. All these results are therefore obtained by staying very close to the surface of the Earth: a parabolic flight takes place at a height of about 10 kilometers and the ISS is only 400 kilometers from the Earth.

This article originally appeared on The Conversation. Read the original.

Hervé Caps receives funding from ESA, ULiège and Belspo. He is responsible for “La Maison de la Science”, the science museum at ULiège.

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