Gravitation(गुरूत्वाकर्षण)-mpsc science

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Intro of Gravitation(गुरूत्वाकर्षण)

➤ Gravitation or just gravity is the force of attraction between any two bodies.
➤ All the objects in the universe attract each other with a certain amount of force, but in most of the cases, the force is too weak to be observed due to the very large distance of separation.
➤ Besides, gravity’s range is infinite but the effect becomes weaker as objects move away.
➤ This force of attraction was first observed by Sir Isaac Newton and was presented as Newton’s law of gravitation in the year 1680. However, gravitation can generally exist in two main instances.
➤ Gravitational force is a central force which depends only on the position of test mass from the source mass and always acts along the line joining the centres of the two masses.
Gravitation may be the attraction of objects by the earth
➤Example:
➤If a body (ball) is thrown upwards, it reaches a certain height and falls downwards because of the gravity of the earth.
Gravitation may be the attraction of objects in outer space.
➤ Example:
➤ Force of attraction between the other planets and sun.

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Newtons law of gravitation

➤ According to Newton’s law of gravitation, “Every particle in the universe attracts every other particle with a force whose magnitude is,Directly proportional to the product of their masses
➤i.e. F ? (M1M2) . . . . (1)
➤ Inversely proportional to the square of the distance between their centre
➤i.e. (F ? 1/r2) . . . . (2)
➤ On combining equations (1) and (2) we get,
➤ F ? M1M2/r2
➤ F = G × [M1M2]/r2 . . . .
➤Or, f(r) = GM1M2/r2 [f(r)is a variable, Non-contact, and conservative force]
➤As f(r) varies inversely as a square of ‘r’ it is also known as inverse square law force
➤The proportionality constant (G) in the above equation is known as gravitational constant.
➤The dimension formula of G is [M-1L3T-2]. Also, the value of the gravitational constant,
acceleration due to gravity
➤ A free-falling object has an acceleration of 9.8 m/s/s, downward (on Earth).
➤ This numerical value for the acceleration of a free-falling object is such an important value that it is given a special name
➤It is known as the acceleration of gravity - the acceleration for any object moving under the sole influence of gravity.
➤A matter of fact, this quantity known as the acceleration of gravity is such an important quantity that physicists have a special symbol to denote it - the symbol g.
➤The numerical value for the acceleration of gravity is most accurately known as 9.8 m/s/s.
➤There are slight variations in this numerical value (to the second decimal place) that are dependent primarily upon on altitude.
➤We will occasionally use the approximated value of 10 m/s/s

how gravitation change on earth

➤Earth’s gravity is everywhere, and everything with mass exerts gravitational pull on everything else.
➤ Materials with different densities on Earth’s surface and in its interior influence Earth’s gravitational pull—mountains actually pull plumb bobs toward them because of their large mass compared to the air around them.
➤Gravity is invisible, and it’s everywhere
➤The force of Earth’s gravity pulls us toward the center of Earth’s mass and keeps us standing upright, no matter where we are on the globe.
➤Gravity keeps water in our drinking glasses and food on our plates.
➤It causes apples to fall to the ground.
➤The moon’s gravity pulls on Earth’s water to cause tides.
➤The sun’s gravity keeps Earth in its orbit.
➤Every object with mass exerts a gravitational pull on every other mass, and as an object’s mass increases, its gravitational attraction increases.
➤Objects that are denser have a greater concentration of mass, thus creating a larger gravitational pull than a same-sized object with lower density
➤i.e., a cubic foot of solid rock will exert a larger pull on its surroundings than a cubic foot of ocean.
➤ If you are standing next to a mountain holding a plumb bob, the mountain will exert a gravitational pull on you, so the plumb bob will divert ever so slightly toward it.
➤ Humans don’t feel the slight differences in gravitational pull, but our sensitive instruments do.
➤ If Earth were a homogenous, smooth ellipsoid, then the gravitational pull would be the same everywhere and perpendicular to the surface of the ellipsoid.
➤The ocean surface would also be a perfect ellipsoid.
➤Because Earth is rugged and composed of materials with widely differing densities in three dimensions from its core to its surface, gravitational pull varies.
➤Scientists have defined a bumpy surface called a geoid to describe the long-term average or “mean” configuration of Earth’s gravitational pull.
➤ Everywhere on Earth, water aligns parallel to the geoid, and plumb bobs hang perpendicular to it, pulled by the force of gravity in that specific location.
➤Earth’s gravitational field is constantly shifting because its dynamic surface processes cause local changes in mass that occur on shorter time scales; these changes in the local gravity field can be tracked as the “time-variable” gravity field over periods of years, including the following:
➤Redistribution of mass from tectonic events like volcanic eruptions and earthquakes.
➤Changing mass of polar ice sheets and distribution of ocean currents.
➤ Shifting masses of groundwater and even soil moisture.
➤In SI units: 6.67 × 10-11 Nm2 kg-2,
➤ In CGS units: 6.67×10-8 dyne cm2 g-2

Newton's law of motion
➤ Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics.
➤ They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces.
➤ More precisely, the first law defines the force qualitatively, the second law offers a quantitative measure of the force, and the third asserts that a single isolated force doesn't exist.
➤ These three laws have been expressed in several ways, over nearly three centuries,[a] and can be summarized as follows:

Newton's First law of motion

➤ In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.

Newton's Second law of motion

➤ In an inertial frame of reference, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. (It is assumed here that the mass m is constant – see below.)

Newton's Third law of motion

➤ When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
➤ The three laws of motion were first compiled by Isaac Newton in his Philosophic Naturals Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687.
➤ Newton used them to explain and investigate the motion of many physical objects and systems.
➤ For example, in the third volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion.

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