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.

(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3 ✓ UPSC's answer

Why the answer is (d)

• Tides result from the Moon's gravitational pull (2), the Sun's pull (1, about 46% as strong, producing spring and neap tides), and the centrifugal force of the Earth–Moon system's rotation about their common centre of mass (3), which raises the bulge on the side away from the Moon.

• All three act together.

• Hence 1, 2 and 3, option (d).

Why the other options are wrong

(a) 1 only: The Moon and centrifugal force are also causes.
(b) 2 and 3 only: The Sun also contributes to tides.
(c) 1 and 3 only: The Moon is the main cause of tides.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.