Gravity, often known as gravitation, is a natural phenomena in which all objects with mass or energy, including planets, stars, galaxies, and even light, are drawn to (or gravitate toward) one another. Gravity gives physical objects weight on Earth, and the Moon’s gravity causes ocean tides.
What is Gravity
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The gravitational attraction of the Universe’s original gaseous matter caused it to begin coalescing and forming stars, and the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, but its effects weaken as objects move further away.
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Gravity is most precisely defined by Albert Einstein’s general theory of relativity (introduced in 1915), which depicts gravity as a result of masses travelling along geodesic lines in a curved spacetime produced by the unequal distribution of mass.
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A black hole is the most extreme example of this curvature of spacetime, from which nothing—not even light—can escape once past the event horizon.
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Gravity is well approximated for most applications by Newton’s law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them.
Below show a table of different acceleration due to gravity of the planets in the solar sysem
| Body | Mass (kg) | Radius (m) | m/s² to gravity (g) in Acceleration due |
|---|---|---|---|
| Sun | 1.99 X 1030 | 6.96 X 108 | 274.13 |
| Mercury | 3.18 X 1023 | 2.43 X 106 | 3.59 |
| Venus | 4.88 X 1024 | 6.06 X 106 | 8.87 |
| Earth | 5.98 X 1024 | 6.38 X 106 | 9.81 |
| Moon | 7.36 X 1022 | 1.74 X 106 | 1.62 |
| Mars | 6.42 X 1023 | 3.37 X 106 | 3.77 |
| Jupiter | 1.90 X 1027 | 6.99 X 107 | 25.95 |
| Saturn | 5.68 X 1026 | 5.85 X 107 | 11.08 |
| Uranus | 8.68 X 1025 | 2.33 X 107 | 10.67 |
| Neptune | 1.03 X 1026 | 2.21 X 107 | 14.07 |
| Pluto | 1.40 X 1022 | 1.50 X 106 | 0.42 |
The Evolution of Gravitational Theory
The ancient world
Archimedes, an ancient Greek philosopher, discovered the centre of gravity of a triangle. He also proposed that if two equal weights did not share the same centre of gravity, the centre of gravity of the two weights combined would be in the middle of the line connecting their centres of gravity.
In De Architectura, the Roman architect and engineer Vitruvius proposed that gravity of an item was determined by its “nature” rather than its weight.
Aryabhata, an Indian mathematician-astronomer, discovered gravity to explain why things do not spin off as the Earth rotates, while Brahmagupta characterised gravity as an attracting force and coined the word gurudwara for gravity.
Revolution in Science
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Various Europeans experimentally disproved the Aristotelian notion that heavier objects fall faster in the mid-16th century. Galileo Galilei showed (possibly as a thought experiment) in the late 16th century that two balls of various weights thrown from a tower would fall at the same pace.
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Galileo demonstrated that gravitational acceleration is the same for all things by combining this knowledge with precise observations of balls sliding downslope.
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Galileo proposed that objects with a low density and a large surface area fall more slowly in an atmosphere due to air resistance. Galileo accurately postulated in 1604, that the distance travelled by a falling object is proportional to the square of the time passed.
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Between 1640 and 1650, Italian Jesuits Grimaldi and Riccioli verified the relationship between the distance of objects in free fall and the square of the time required. They also calculated the gravity of the Earth by measuring the oscillations of a pendulum.
Newton’s gravitational theory
In 1679, English mathematician Isaac Newton received a letter from Robert Hooke outlining his concept about orbital motion, which is based in part on an inverse-square force. Hooke and Newton both assured Edmond Halley in 1684 that they had verified the inverse-square rule of planetary motion.
Hooke declined to publish his arguments, but Newton did, in De motu corporum in gyrum (‘On the Motion of Bodies in an Orbit,’ from which he derived Kepler’s equations of planetary motion.
Newton’s development of his work into the Philosophi Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), in which he hypothesises the inverse-square rule of global gravity, was endorsed by Halley.
Newton “deduced that the forces which keep the planets in their orbs must be reciprocal as the squares of their distances from the centres about which they revolve: and thus compared the force required to keep the Moon in her Orb with the force of gravity at the surface of the Earth, and found them to answer pretty nearly,” according to Newton.
The principle of equivalence
The equivalence principle, investigated by a number of scientists including Galileo, Loránd Eötvös, and Einstein, represents the concept that all things fall in the same manner, and that the effects of gravity are indistinguishable from certain characteristics of acceleration and deceleration.
The easiest approach to test the weak equivalence principle is to drop two items of differing weights or compositions into a vacuum and see whether they land on the same spot.
When additional forces (such as air resistance and electromagnetic effects) are insignificant, such studies show that all items fall at the same pace. More complex testing use an Eötvös-invented torsion balance. Satellite experiments, such as STEP, are being designed for more precise space tests.
The following are several formulations of the equivalence principle:
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The weak equivalence principle states that the trajectory of a point mass in a gravitational field is independent of its composition and is determined only by its starting location
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The principle of Einsteinian equivalence: Any local non-gravitational experiment in a freely falling laboratory produces results that are independent of the laboratory’s velocity and position in spacetime.
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The strong equivalence principle necessitates both of the preceding.
Quantum mechanics and gravity
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The topic of whether gravity’s small-scale interactions can be described using the same framework as quantum physics remains unanswered.
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General relativity explains large-scale bulk features, while quantum mechanics describes matter’s tiniest scale interactions.
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One approach would be to define gravity within the framework of quantum field theory, which has been shown to adequately represent the other basic interactions.
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The electromagnetic force is generated by an exchange of virtual photons, while gravity is caused by an exchange of virtual gravitons, according to the QFT model.
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In the classical limit, this description reproduces general relativity. However, for small distances on the order of the Planck length, this technique fails, necessitating a more thorough theory of quantum gravity (or a new approach to quantum mechanics).
Relativity in general
In general relativity, gravitational effects are attributed to spacetime curvature rather than a force. The equivalence principle, which equates free fall with inertial motion and characterises free-falling inertial objects as being accelerated relative to non-inertial observers on the ground, is the starting point for general relativity.
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Einstein hypothesised that matter curvatures spacetime, and that free-falling objects move along locally straight trajectories in curved spacetime. Geodesics are the name given to these straight pathways.
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Einstein’s hypothesis, like Newton’s first rule of motion, asserts that if a force is applied to an object, it will diverge from a geodesic.
For example, we no longer follow geodesics when standing since the mechanical resistance of the Earth exerts an upward push on us, and as a consequence, we are non-inertial on the ground. This explains why travelling along spacetime’s geodesics is considered inertial.
Summaray
In general, heavier things have a larger gravitational pull. Gravity weakens as you go farther away. This means that two objects are more closely spaced if their gravitational pulls are stronger.
Anomalies and disparities
Some observations are not fully accounted for, which may hint at the need for improved gravity theories or may be explained in other ways.
Extra-fast stars
Stars in galaxies follow a velocity distribution in which stars on the periphery move faster than they should based on observable distributions of normal stuff. A similar pattern may be seen in galaxies inside galactic clusters.
The mismatch might be explained by dark matter, which interacts gravitationally but not electromagnetically. Various Newtonian dynamics modifications have also been suggested.
Accelerating expansion
It seems that the metric expansion of space is accelerating. Dark energy has been presented as a possible explanation.
A new alternate interpretation is that the geometry of space is not homogenous (owing to clusters of galaxies), and that when the data is reinterpreted to account for this, the expansion does not speed up after all, however this result is challenged.
An unusual rise in the astronomical unit:
Recent studies show that planetary orbits are broadening faster than expected if the Sun is losing mass via radiating radiation.
Extra energetic photons:
Photons passing through galaxy clusters should acquire energy before losing it on the way out.
Even though the rapid expansion of the Universe should prevent photons from recovering all of their energy, photons from cosmic microwave background radiation acquire twice as much energy as predicted.
Extra massive hydrogen clouds:
The spectral lines of the Lyman-alpha forest show that hydrogen clouds are more clumped together than predicted at certain scales, which, like dark flow, may imply that gravity goes off faster than inverse-squared at certain distance scales.
Summary
Gravity is created by masses travelling along geodesic lines in curved spacetime, according to Albert Einstein’s General Theory of Relativity. Grimaldi and Riccioli, two Italian Jesuits, demonstrated that gravity is proportional to time squared.
Frequently Asked Questions
People usually ask many about Gravity. A few of them are discussed below:
1. How is gravity created?
Gravity is an unseen force that attracts items to each other. As a result, the greater the gravitational force of two things, the closer they are to each other. The gravity of the Earth is caused by all of its mass. All of its mass exerts a cumulative gravitational force on all of your body’s mass.
2. What exactly is gravitational power?
Gravitational energy, also known as gravitational potential energy, is the potential energy possessed by a big object in relation to another enormous object as a result of gravity. It is the gravitational field’s potential energy that is released (turned into kinetic energy) as the objects descend towards one other.
3. What are the third gravitational laws?
According to the first law, an object’s motion will not alter until a force acts on it. According to the second law, the force acting on an object is equal to its mass multiplied by its acceleration.
When two objects contact, they apply forces of equal magnitude and opposing direction to each other, according to the third law.
4. Is gravity caused by time?
Yes, time moves quicker the further you are from the earth’s surface compared to time on the earth’s surface. This is referred to as “gravitational time dilation.” Gravitational time dilation happens when objects with a high mass generate a strong gravitational field.
5. Where does gravity exist in space?
Some individuals believe that gravity does not exist in space. In truth, there is a minor amount of gravity everywhere in space. Gravity keeps the moon in orbit around Earth. The sun is orbited by Earth due to gravity.
Conclusion
The path of a point mass in a gravitational field is determined simply by its starting position and velocity, according to Einstein’s equivalence principle. The question of whether gravity’s small-scale interactions may be expressed using the framework of quantum physics remains unanswered. Gravity is a natural phenomenon that causes all objects with mass or energy to be drawn to (or gravitate toward) one another.
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