UPSC Prelims 2015 Question:

Tides occur in the oceans and seas due to which among the following?

1. Gravitational force of the Sun
2. Gravitational force of the Moon
3. Centrifugal force of the Earth
   
   

Select the correct answer using the code given below:

Explanation:

• The rhythmic rise and fall of ocean water twice in a day is called a tide. It is high tide when water covers much of the shore by rising to its highest level. It is low tide when water falls to its lowest level and recedes from the shore.
  
  

• The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides. The water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force and causes high tide. During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides. But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of the sun and moon resulting in low tides. These tides are called neap tides. So, points 1 and 2 are correct.
  
  
• Centrifugal force is the force directed away from the center of rotation. As the Earth revolves on its axis, centrifugal force attempts to throw objects from the Earth’s surface into space. If earth’s gravity was sufficiently weak or its speed of rotation sufficiently great, objects would be hurled into space.  As the earth travels in its orbit about the Sun, centrifugal force acts on the side of the earth away from the Sun and attempts to fling the Ocean into space. Gravitational attraction between the earth and ocean is greater than centrifugal force and the ocean remains on the earth, but a tidal bulge is produced. So, point 3 is correct.
  
  

Therefore, option (4) is the correct answer.

Subject: Geography | Oceanography