The Force of Gravity
1. The gravitational force is the weakest of the four fundamental forces, and it is the force that attracts all objects with mass. It is referred to as attractive due to the fact that it always pulls masses together, and never causes them to be pushed them apart. All objects with mass are affected by gravity, and there is no way to cancel gravity out for an object with mass on Earth. The force of gravity on a singular object on Earth is always found by the equation: Fg= mg where g = 9.8m/s^2 and m = mass (in kg).
The study of gravity is questionably the least comprehensible in the history of physics. Decade after decade, scientists have studied particle interaction in respect to gravity, but various concepts of the presence of gravitational particles remain undetermined. But, there is a proposed theory of a type of particle called “gravitons”. The graviton is a hypothetical particle that creates/ balances the force of gravitation in the framework known as the quantum field theory (the theoretical framework for the construction of quantum mechanical models of subatomic particles within the study of particle physics). Yet, this theory of gravitons is merely hypothetical (as no one has ever proven a detection of gravitons). The primary reason that gravitons have been proven more difficult to study and detect than other particles including photons, is that numerous other variations of particles do not interact with other particles that are the same as them. For example, photons are unable to interact with photons (they obtain the same electromagnetic force, yet they are not charged themselves and refrain from interaction with this force). Extensively, photons are said to obtain mass and interact with gravity, but not with their own forces. Similarly to photons, gravitons are also said to carry mass, but gravitons do carry the gravitational force which interacts with this mass. As well as gravitons being required to have interactions with other gravitons, quantum mechanics suggests that they must also interact with themselves through “virtual particles”. Comprehension of these interactions is completely different than understanding the kinds of interactions that other particles have, and is what ultimately resulted in incompletion of theory.
2. The first scientist to question the relativity between the Earth and mass was Aristotle. Aristotle had the idea that if an object fell to Earth it was because it was attracted to its “natural place”. He theorized that heavier object fall faster, and mass was inherent to an object.
Galileo in the late 16th – early 17th century:
brought scientific experiments into the picture
discovered that a heavy object and a light object can actually fall at the same speed and they usually fall at different speeds due to air resistance rather than gravity
discovered that objects always descend with an acceleration which is constant and along a parabolic curve
Newton in the second half of the 17th century:
developed a universal law of gravity
suspected that the attraction between two objects on Earth was equal to the result of their masses divided the distance between them, squared
Einstein in the early 19th century:
grasped that gravity and acceleration are (in theory) the same thing
his General Theory of Relativity, which he formulated in 1915, explained how gravity is a consequence of the way that mass curves "spacetime," which is known as the fabric of the universe. He looked at it from a perspective of geometry. He found that objects that are in motion travel through space and time on the path of the lowest level of resistance, or a planet will orbit a star, not due to its connection to the star through a variation of an invisible tether, but rather due to the fact that the space is warped (surrounding the star.)
A predictions of one of Einstein’s equations (although he, himself was not fully invested in his theories regarding this) was the existence of gravitational waves
LIGO in the 1960s:
University of Maryland physicist Joseph Weber constructed devices intended for the detection of gravitational waves, and he claimed to have evidence of success but was unable to prove this
These devices were the roots of the now-famous “Laser Interferometer Gravitational-Wave Observatory”
Gravitational waves are believed to pass through everything and can't be directly captured, so the two LIGO facilities used a laser beam to try to deduce the passing of a gravitational wave
99 years following Albert Einstein’s prediction of the existence of gravitational waves, two Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) laser interferometers were able to detect a signal of two of black holes (which were of masses both 29 and 36 times the mass of the sun) merging together (2016). Gravitational waves are said to be in relation to to sound waves as they make things vibrate. The detectors used in LIGO are referred to as “bionic ears” and they allow scientists to “listen” to the universe. The signal said to be found from the two black holes began at two octaves below the sound middle C and went up to the sound middle C in approximately one-tenth of a second. These signals were closely accurate to predictions, and displayed absolutely no symbols of deviation from Einstein’s theories regarding the detection of gravitational waves. Within the present day, LIGO is the most prominent source used to detect gravitational waves, as the study of gravitons and these waves are still incomprehensible. The technology created by American scientists is still the primary resources used for the detection of gravitational waves by various scientists around the world today.
Below is CalTech’s simplified explanation of how this laser LIGO device operates in the modern day:
3. Example 1: Why the Planets Orbit the Sun
Newton came to the realization that the cause of the planets orbiting the Sun correlates directly with why objects fall towards/ to the Earth when we drop them. The Sun's gravity is able to pull on the planets, in the same sense that the Earth's gravity is able to pulls down all objects that are not held up by other forces (and in result, keeps our feet on the ground). As we know, objects with more mass produce larger gravitational pulls than lighter ones. Therefore, as the heavyweight within our solar system, the Sun exerts the strongest of gravitational pulls.
On top of falling toward the Sun, the planets all move sideways. Similarly to a scenario in which you were to have a weight on the end of a string (i.e. if you swing it around, you are constantly pulling it toward your hand, but the motion sideways keeps the ball swinging around) the gravity of the Sun pulls the planet in. Without that sideways motion, it would fall to the center; and without the pull toward the center, it would go flying off in a straight line, which is, of course, exactly what happens if you let go of the string. Conclusively, the force of gravity attracts the mass of the Earth to the mass of the sun.
Example 2: Why a Feather Falls Slower than a Baseball When Dropped From the Same Initial Point
Many wonder why it is that a feather would fall at a slower pace than a baseball when dropped from the same initial point. It's because the air offers much greater resistance to the falling motion of the feather than it does to the brick. The air is actually an upward force of friction, acting against gravity and slowing down the rate at which the feather falls. The ball, on the other hand, can cut right through the air as if it didn't exist. As, said before, Galileo discovered that objects that are more dense, or have more mass, fall at a faster rate than less dense objects – but this is not because of mass but rather air resistance. If a feather and a brick were dropped together in a vacuum (in other words, an area from which all air has been removed) they would fall towards the ground at the same rate, and hit the ground at exact same time. This is because the rate at which an object falls through the air doesn’t depend thoroughly on the weight of an object/ the force of gravity if air resistance is taken into consideration.
Example 3: How Gravity Works in Rock-Climbing (along with Fn, Ft and Ff)
When you are rock climbing you have to pull yourself up to keep going. Without gravity it would be easy to climb because nothing would be pushing you down. The force of gravity pushes you down, making is considerably harder to keep going. Newton's First Law plays a huge role in this because without the force of gravity you could stay in motion while going up but with gravity you are forced to rest. Gravity is the unbalanced force acting against you. This is why the tension in the rope holding the climber, the friction of the cliff and the normal force between the cliff and the climber's shoe are needed- without them the force of gravity would make it very dangerous for the climber, as it would continually f, causing them to possibly fall if they weren’t strong enough.