Gravitational Force is introduced by the Laws of Motion in which force requires energy. The gravitational force has attraction and repulsion power. The heavenly bodies are governed by this force and make the sky how deep we wish we knew. Gravitational force scatters in the universe.

 Why do the space travelers and objects in the spacecraft appear floating?

Introduction to Scientist:

1) Sir Issac Newton ( 25 Dec. 1642 - 20th Mar. 1727) :

      He was born in England. His book Philosophia Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) was first published in 1687 and laid the foundations of classical mechanics. He gave his laws of motion, equation of motion, and theory of gravity in this book. Newton used his mathematical description of gravity to prove Kepler's laws of planetary motion and other phenomena as eradicating doubt about the heliocentric Solar System. Newton mathematically derived Kepler's laws. He demonstrated that the same principles could account for the motion of objects on Earth and celestial bodies.
          Newton did groundbreaking work in several areas including light, heat, and sound. He built the first practical reflecting telescope and developed a sophisticated theory of color based on the observation that a prism separates white light into the colors of the visible spectrum. His work on light was collected in his highly influential book Optiks which was published in 1704. He also formulated an empirical law of cooling and made the first theoretical calculation of the speed of sound; and introduced the notion of a Newtonian fluid. He invented a new branch of mathematics is called calculus, as a mathematician, Newton contributed to the study of power series, generalized the binomial theorem to non-integer exponents; developed a method for the roots of a function, and classified most of the cubic plane curves.

The gravitational force is a universal force. The law of gravitation was first discovered by Sir Issac Newton who discovered the force attraction by seeing an apple fall from a tree and he found that an apple falls vertically downwards and the force on an apple is towards the center of the earth.

  • What is mean by Force?
  • What types of forces are you familiar with?
  • What do you know about the gravitational force?

Concepts:

1) Force :

      "A force is essential to change the speed and the direction of motion of an object."

2) Centripetal Force:

       "A force acts on any object moving along a circle and it is directed towards the center of the circle is called Centripetal Force." the object tries to go towards the center of the circle because of the centripetal force. It is the center-seeking process. The centripetal force is the force acting on the planet and is responsible for its circular motion. It must be inversely proportional to the square of the distance between the planet and the Sun.

 3) Earth's Gravitational Force :

The earth exerts a gravitational force on objects near it. A force acting on a body results in its acceleration. Thus, the gravitational force due to the earth on a body results in its acceleration is called acceleration due to gravity which is denoted by "g."

4) Free Fall :

When any object moves under the influence of the force of gravity alone is called Free Fall.

5) Escape Velocity :

1) The value of "g" keeps decreasing as a body goes higher above the surface of the earth and the gravitational force pulling the body downward decreases. If we increase the initial velocity the body goes high and overcomes the downward pull by the earth and can escape the earth forever and will not fall on the earth back is called Escape Velocity.

Kepler's Laws :

He stated three laws about a planetary motion which are known as Kepler's Laws. The planetary data were available by the 16th century. Using this data, he stated certain laws. They are the following:

Keplers 1st law :

"The orbit of a planet is an ellipse with the sun at one of the foci." It depicts that the planets revolve around the sun in an elliptical orbit.

Keplers 2nd Law :

"The line joining the planet and the Sun sweeps equal areas in equal interval of time." Though the orbit is elliptical, the distance in which planets travel around the Sun is equal in time and area.

Keplers 3rd law :

"The square of its period of revolution around the sun is directly proportional to the cube of the mean distance of a planet from the Sun." 

    T^2 a r^3  or   T^2/r^3 = constant / K
We squared the period of revolution which is directly proportional to cubic mean distance. The most important thing in it is the Squared period of revolution and the mean distance from the Sun.


Gravitational Force | Laws of Motion | School Academy
Gravitational Force Equation

When these facts came before, Newton formulates the theory of Universal Gravity. because Kepler had no explanation of why the planets obey these laws, just he stated the truth only before the world. But the real explanation was given by Newton. 

Before we go ahead, we must understand the laws of motion as follows:

Newton's Laws of Motion :

Newtons 1st Law of Motion :

Newton's first law of motion depends on the balanced and unbalanced force.
"An object continues to remain at rest or in a state of uniform motion along a straight line unless an external unbalanced force acts on it."

Newtons 2nd Law of Motion :

This law is also known as the law of Momentum.
"The rate  of change of momentum is proportional to the applied force and the change of momentum occurs in the direction of the force." Momentum is the product of the mass and velocity of an object.  P= mv.
“The rate of change of momentum is proportional to the applied force and the change of momentum occurs in the direction of the force.

Newtons 3rd Law of Motion :

" Every action force, there is always an equal and opposite reaction force which acts simultaneously."

These three laws of motion could explain well the theory of Kepler's Laws. But the main thing in it is the Universal Gravitational force which is acting on every aspect of the universe.

Newtons Universal Law of Gravitation:

"Everybody in the universe attracts every object with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them."
         F = G( m1m2/ d^2)
That is if the mass of one object is doubled, the force between the two objects also doubles and if the distance is doubled, the force decreases by a factor of four. If two bodies are spherical, the direction of the force is always along the line joining the center of the two bodies, and the distance between the centers is taken to be "d".