Thursday , April 9 2020

NCERT Class 7th (CBSE) Social Science: The Hydrosphere

Question: Differentiate between: Crest and Trough; Waves and tides; Spring and Neap tides; Current and drift.

Answer: Difference is as follows:

Crest and Trough

The rise of water in a wave is called crest.
The fall of water in a wave is called trough.

Waves and Tides

1. The rise and fall of surface water in the ocean or sea is called wave.
1. The alternate rise and fall in the level of sea and ocean water twice a day at regular intervals is called tides.
2. They are formed when the wind blows across the water surface.
2. They are caused due to the gravitational pull of the moon and the sun on the earth’s surface.

Spring and Neap Tides

Spring Tides
Neap Tides
On full moon and new moon, the sun, the moon and the earth are almost in a straight line. The sun and the moon exert a combined gravitational pull. The high tides are the highest and low tides are the lowest. The phenomenon is known as spring tide.
On Half moon day, the sun and the moon make a right angle to the earth. Thus, the gravitational pull of the sun and the moon tends to cancel each other. This results in a very small rise or fall in sea water and is known as neap tide.

Current and Drift

The movement of ocean water in the form of a stream, in a definite direction on the ocean surface is called an ocean current.
The very broad ocean currents are called drift.

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One comment

  1. This is very helpful to all.

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