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Zero gravity Gravitation plays a major role in so many aspects of our lives. Gravity acts on every object with out any distinction. As the height increases, the amount of gravitational pull decreases. Therefore the object starts to float in space. Lets Learn more about the gravitation and how it varies with height of the ground, in this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Explore the basic force that rules the Nature, i.e., gravitation and expand its importance in everyday science.
  • Clearly observe and reflect on the Kepler's laws of planetary motion.
  • State and relate the Newton's universal law of gravitation to everyday science.
  • Observe and reflect on the variation of acceleration due to gravity at different places of Earth.
  • Distinguish between mass and weight of the object.
  • Discover the concept of weightlessness and apply it to everyday science.
  • Explore about the ocean tides and extend it to different types of tides.
  • Explore and discuss about gravitational potential energy.
  • Investigate, explore and formulate Kepler's laws of planetary motion.
  • Develop and formulate orbital velocity, escape velocity and energy of artificial satellites.
Spiral_Galaxy Spiral galaxy The Milky Way is one of the larger spiral galaxies. They are bright and distinctly disk–shaped, with hot gas, dust and bright stars in the spiral arms and a central concentration of stars known as bulge.

The force that binds the planets, billions of stars, including the sun and solar system is the same force that holds the moon in orbit and you on earth – gravitational force.

Polish astronomer Nicolaus Copernicus and later Danish astronomer Tycho Brahe, made extensive research regarding the positions of the planets in the sky and their motions. Brahe recorded the planet's positions for 20 years to 1/60 of a degree using a huge brass protractor–like instruments called quadrants. Brahe's younger colleague, German Johannes Kepler, edited and published Brahe's planetary tables. From the data, Kepler discovered some very remarkable and simple laws regarding planetary motion.

Soon after Kepler, Galileo did some remarkable observation regarding motion of Jupiter's moon. He noticed that they obeyed Kepler's laws too. After Galileo, another scientist Isaac Newton, with his innovative mind, unravelled what was happening to the motion of heavenly bodies. He was able to recognize that the force which was responsible for the motion of the planets around the Sun, or the Moon around the earth, was the same force that was responsible for making the apple fall towards the earth. This force is the famous gravitational force!

Keplers laws Kepler's laws Kepler determined three laws characterizing orbital motion, using Tycho Brahe's planetary observation data. These laws can be proven mathematically using Newton's law of gravitation. These laws apply directly to satellite orbital motion.
Kepler's laws of planetary motion

After Tycho Brahe's death, Kepler converted Brahe's measurements of planets' positions to values that would be obtained by a stationary observer outside the solar system. Kepler's expectations were that the planets would move on perfect circles around the Sun. But this was shattered after several years of effort. He found the paths to be ellipses. He wrote down his observations as three laws and these are known as Kepler's laws of planetary motion.

Kepler's first law

Each planet moves in an elliptical orbit with the sun at one focus of the ellipse.

It is also known as law of orbit or is sometimes referred to as the law of ellipses. It explains that planets are orbiting the Sun in a path described as an ellipse.

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