What is gravity?
The four basic fundamental physical forces that exist in nature are: weak nuclear force, strong nuclear force, electromagnetic force, and gravity. Out of all these forces, gravity is the weakest. Gravity is a force that is always present. It pulls objects toward each other. It helped shape the universe. Gravity also affects life on Earth. Newton’s law of gravitation is about how objects pull on each other. Every object in the universe attracts every other object. The force of this attraction depends on two things. First, it depends on the product of their masses. Mass is the amount of matter in an object. Second, the force gets weaker with more distance. It decreases as the square of the distance between them gets larger.
Newton’s law of gravitation
The equation expresses the law in mathematical form as follows:
From the above equation, we see that the small mass body m₁ has a very tiny effect on the acceleration of the large mass body m₂. Small mass bodies include living beings like humans, plants, and animals. Large mass bodies include objects like Earth. The effect is so minimal, yet consistently present, that the larger body inevitably pulls the smaller body toward it. Furthermore, this gravitational interaction guarantees that the larger body continues to exert a force on the smaller body, influencing it regardless of the distance between them.
As a result, the larger body’s dominance in this dynamic remains both persistent and unavoidable, establishing a constant and unyielding gravitational pull. Consequently, this force remains a fundamental aspect of the relationship between the two bodies. Everything on the surface of Earth is affected by Earth’s gravity.
Earth’s Gravity: The 1g Environment
Earth’s gravity is known as the “1g environment.” This means it is the standard measure of gravitational pull on Earth. Strength makes this force influence objects. It includes an apple that fell on Newton’s head, a burning candle or a falling water droplet, humans anchored to the Earth’s surface, and many other phenomena. The question is: how do we study these effects?
To embark on a journey of unraveling the mysteries of gravity and its pivotal role in shaping life forms, it is essential to adjust its magnitude while keeping other physical parameters constant in order to understand its effects more comprehensively. In fact, the removal of gravity becomes a desirable, and even necessary, step toward gaining a deeper understanding of its role in living organisms. In a sense, the removal of gravity for studying sensing mechanisms is akin to switching off the light in order to study the role of vision. Before we can fully grasp its effects, let’s first explore how we can manipulate gravity to facilitate our studies.
How can gravitation be altered?
Different planets exhibit different gravity based on their mass and radius. Understanding it’s changes is important for science and engineering. This includes fields like astronomy, space biology, and space exploration. Different astronomical bodies have varying levels. This is because of their mass, size, and density. Table 1 below shows this information.
Gravity is classified by acceleration into three categories: microgravity (ranging from 10ˉ³g to 10ˉ⁶g), hypogravity (greater than 10ˉ³g but less than 1g), and hypergravity (more than 1g), with 1g representing Earth’s gravity (9.8 m/s²). Modern space technology facilitates microgravity experiments through the use of parabolic flights, drop towers, and sounding rockets. Specifically, parabolic flights offer approximately 25 seconds of 0g by climbing, leveling off, and then descending in a controlled arc. On the other hand, drop towers, which operate in a vacuum, allow objects to experience microgravity as they fall from a height for a few seconds. These methods provide valuable opportunities for studying the effects of reduced gravity, although the duration of exposure is limited..
Microgravity
Facilities such as parabolic flights, drop towers, and sounding rockets are specifically designed to create a microgravity environment, which is a condition where people or objects appear to be weightless. However, these facilities come with a notable disadvantage: they only provide a brief period for exposure to microgravity. As a result, scientists predominantly conduct gravity experiments on the ground. These ground-based experiments, in fact, serve as the primary method for studying how living organisms respond to gravity. On Earth, researchers, therefore, utilize specialized machines that simulate an environment similar to microgravity, allowing for more extended studies. In this context, microgravity refers to a condition where gravitational forces are extremely weak, much like those experienced in space. Consequently, objects in this environment appear to be weightless, which in turn provides valuable insights into the effects of gravity on biological systems.
Hypergravity and Its Role in Research
Some useful machines for this purpose include clinostats, random positioning machines, rotating wall vessels, and magnetic levitation devices. Each of these machines operates in a unique way to mimic the feeling of weightlessness in space. For instance, during centrifugation, we use acceleration to generate powerful gravity, commonly referred to as hypergravity. This allows us to study how living organisms sense and react to in various conditions. Furthermore, these machines provide valuable insights into the adaptive mechanisms of organisms in response to gravitational changes, enhancing our understanding role in biological processes.
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