Solutions-Class-7-Geography-Chapter-3-Tides-Maharashtra Board

• The moon is more closed to the earth, than the sun.
• Therefore effect of the gravitational force of the moon becomes more effective than that of the sun.
• Therefore, tides are influenced more by the moon than the sun.

• Due to tides Low-lying areas along the coast are flooded and drained by the salt water.
• This process generates a gradual deposition of some sea water and sediment in the low-lying areas.
• In such region, plants then take root and hold the soil firmly against the forces of tides and waves.
• This gradually helps in maintaining mangroves and the coastal biodiversity in the low-lying areas.
• In this way, at some places along the coast, the low-lying areas turn into lagoons or marshy lands.

(1) The gravitational force of the moon exceeds the earth’s centrifugal force, when a particular place (located on particular meridian) faces the moon. As its effect, the water is pulled towards the moon.

(2) At the same time, at antipodal location (on the opposite meridian), the centrifugal force of the earth exceeds the gravitational force of the moon. The water is pulled in the direction away from the moon. This causes high tides at these two places.

When there is high tide at 0° meridian, the 180° meridian also experiences high tide.

(3) The water required for the high tides moves in from the places on the two opposite meridians that are at right angles to those having high tides causing low tide at those places.

Thus place located on the opposite meridian to the place experiencing high or low tide will also experience high or low tide respectively.

If there is high tide at 7 am, the timings of the next low tide and high tide will be approximately 1.12 pm. and 7.25 pm respectively.

Reason: There is high tide and low tide twice a day (24 hours) generally. The time difference between two high tides is of 12 hours and 25 minutes.

Mumbai located on 78° E meridian and 107° W meridian is exactly opposite to the 73° E meridian. If there is high tide at 1.00 pm on Thursday, then, on 107° W meridian too, there will be high tide,

Reasons : (1) A place on the earth located at the opposite point of the place experiencing high or low tide also experiences high or low tide respectively at the same time.

(1) The main reason for the generation of waves is wind

(2) Sometimes, sea waves are also generated due to earthquakes or volcanic eruptions occurring below the floor of the sea.

(1) Swimming : We must have adequate information of timings of the tides While entering the sea for swimming, low tide can pull the swimmer deep in the sea, unknowingly. Swimming in a deep sea during tides can lead to serious accidents.

During high tides, it is always safe to swim in shallow waters near coast.

(2) Steering a ship : Ships can move up to the ports during high tides. Therefore, one must steer a ship by taking into account the timings of the tides.

(3) Fishing : With the high tides, fish move into the creeks. Therefore, fishing is largely carried out at the time of high tide.

(4) Salt pans : During the high tide, sea water stored in salt pans. We can obtain salt from this water.

(5) Going to coastal areas for trips : While going to coastal areas for trips, one must have details about the timings of the tides, physical structure, slope of the coast, sudden deep area, rocky areas, streams near the coast before entering the sea waters for enjoyments.

The diagram shows a phase of quarter moon.

The relative positions of the moon, the sun and the earth are such that the moon, the earth and the sun make an angle of 90°

Such positions of the moon, the earth and sun will lead to neap tides.

Positive effect :

1.With the high tide, fish move into the creeks and this helps fishing activity.

2.The tides clear the waste and hence the coasts become clean.

3. Ports do not get filled with sediments.

4. Ships can move up to the ports during high tide.

5. During high tide, sea water can be stored in salt pans from which salt can be obtained.

6. The tidal force can be used to generate electricity.

7. The tides help in maintaining the mangroves and the coastal biodiversity.

Negative Effect :

8. A lack of an understanding of the timings of high and low tides may cause accidents to swimmers entering the sea.