Science 1

• Index


  • Gravitation

  2. Periodic Classication of Element

  3. Chemical reactions and equations

  4. Effects of electric current

  5. Heat

  6. Refraction of light

  7. Lenses

  8. Metallugy

  9. Carbon compounds

  10. Space Missions
• Gravitation


  The universal force that acts between any two objects in the universe
• The phenomenon of gravitation was discovered by Sir Isaac Newton.
• Newton discovered the force of gravitation by seeing an apple fall from a tree on the ground.
• Newton concluded that the earth must be attracting the apple towards itself and this attractive force must be directed towards the center of the earth.
• The direction from the apple on the tree to the center of the earth is the vertical direction at the position of the apple and thus, the apple falls vertically downwards.
• Topics related to gravitation


  • Circular motion and centripetal force
  • Kepler's laws
  • Newton's universal law of gravitation
  • Acceleration due to the gravitational force of the Earth
  • Free fall
  • Escape velocity
• Newton thought that if the force of gravitation acts on apples on the tree at different heights from the surface of the earth, can it also act on objects at even greater heights, much farther away from the earth, like for example, the moon? Can it act on even farther objects like the other planets and the Sun?
• A force is necessary to change the speed as well as the direction of motion of an object.
• Sir Isaac Newton (1642-1727) was one of the greatest scientists of recent times. He gave his laws of motion, equations of motion and theory of gravity in his book Principia.
• Before Newton's book was written, Kepler had given three laws describing planetary motions. However, the reason why planets move in the way described by Kepler's laws was not known. Newton, with his theory of gravity, mathematically derived Kepler's laws.
• In addition to this, Newton did ground breaking work in several areas including light, heat, sound and mathematics. He invented a new branch of mathematics called calculus and has wide ranging applications in physics and mathematics. He was the first scientist to construct a reflecting telescope.
• For the moon to go around the earth, there must be a force which is exerted on the moon and this force must be exerted by the earth which attracts the moon towards itself. Similarly, the Sun must be attracting the planets, including the earth, towards itself.
• Centripetal force


  The force that acts on any object moving along a circle and is directed towards the centre of the circle
• An ellipse is the curve obtained when a cone is cut by an inclined plane. It has two focal points. The sum of the distances to the two focal points from every point on the curve is constant.
• Kepler's laws


  • The orbit of a planet is an ellipse with the Sun at one of the foci
  • The line joining the planet and the Sun sweeps equal areas in equal intervals of time
  • 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
• Kepler obtained these laws simply from the study of the positions of planets obtained by regular observations. He had no explanation as to why planets obey these laws.
• Newton's universal law of gravitation


  Every object in the Universe attracts every other object with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
• The gravitational force is much weaker than other forces in nature but it controls the Universe and decides its future because of the huge masses of planets, stars and other constituents of the Universe.
• Kepler's third law


  T^2 = K * r^2, where T is the time taken and r is the distance
• Mahendra and Virat


  • Masses of 75 kg and 80 kg respectively, distance of 1 m
• Calculating gravitational force between Mahendra and Virat


  1. Use Newton's law of gravitation

  2. F = G * m1 * m2 / r^2

  3. F = 4.002 x 10^-7 N
• The gravitational force between Mahendra and Virat is very small
• Calculating Mahendra's acceleration and velocity towards Virat


  1. Use Newton's laws of motion

  2. a = F/m = 5.34 x 10^-9 m/s^2

  3. v = u + at = 5.34 x 10^-9 m/s
• Mahendra's velocity towards Virat is extremely small
• Mahendra's velocity will increase with time due to increasing acceleration as the distance decreases
• Calculating time for Mahendra to move 1 cm towards Virat


  1. Use v = u + at

  2. t = 1 cm / 5.34 x 10^-9 m/s
• High and low tides occur due to the gravitational force of the moon
• Water directly under the moon gets pulled towards it, causing high tide
• At places 90 degrees from the high tide, low tides occur
• The earth's gravitational force on Mahendra is 1.83 x 10^9 times larger than the force between Mahendra and Virat
• Calculating Mahendra's velocity after 1 second of free fall due to earth's gravity

  1. Use v = u + at

  2. v = 0 + 9.77 m/s = 9.77 m/s
• The acceleration due to gravity g is the same for all objects on the earth's surface
• The value of g is 9.77 m/s^2 on the earth's surface
• The value of g decreases with increasing height above the earth's surface
• The value of g also decreases with depth inside the earth
• Mass is a scalar quantity, weight is a vector quantity
• Weight is the force with which the earth attracts an object
• Weight varies with location, mass does not
• Gravitational waves are predicted by Einstein and recently detected