Q. 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 codes given below.

• 1 only
• 2 and 3 only
• 1 and 3 only
• 1, 2 and 3

Answer: (d) 1, 2 and 3

Notes:

• The periodical rise and fall of the sea level is known as tide.
• The Moon’s gravitational pull is the major cause of a tide.
• Sun’s gravitational pull and centrifugal force due to the gravitational pull of the earth to a lesser extent so causes types.
• The movement of water is caused by Meteorological effects like winds and atmospheric pressure change and is known as surges. 
• The tide-generating force is the difference between the gravitational attraction of the Moon and the centrifugal force.  
• Tides vary in frequency, direction, and movement from place to place and from time to time.
• Based on frequency, they are classified into the semi-diurnal, diurnal, and mixed tide.  
• Springtide: when the sun, moon, and earth are in a straight line the height of the tide is higher and this occurs on a full moon period.
• Neap tide: when the moon and the sun are at right angles to each other the forces of the sun and the moon tend to counteract each other.  It occurs twice a month.