Page 14 - welcome home to DMLS

Delta Modern Language School
Grade 4
Date ......./......./………

Weather: it is condition of atmosphere at a specific time and place.

Weathering: it is breaking down of rocks on earth's surface into smaller

pieces by the effect of wind and water over long periods of time.

❖ Types of Weathering:

1- Mechanical weathering: it is breaking down of rocks due to the effect

of physical factors like wind, water, plant roots and temperature.

➢ Example: -The role of wind in mechanical weathering: -

A. Wind pushes the sand from a place to another.
B. Friction occurs between sand and rocks.
C. Rocks are broken down.

2- Chemical weathering: it is the change of the structure of rocks due to

chemical reactions with some other materials such as: - Oxygen – water
– acid rain – acid produced by some living organisms.

➢ Example: -The role of living organisms in chemical
weathering: -

A. Some tiny organisms called “Lichens” produce
acids on rocks.

B. Acids dissolve minerals found in these rocks.
C. Rocks are broken down.

Lichens: - are tiny plant-like organisms.

Erosion: it is the process in which the small particles of sand, soil and

rocks are moved to other places by wind, water and gravity.
➢ Sediments could be sand, rocks or soil and this depends on the

environment in which the process takes place, they can be moved by
wind and water and settle down on the surface of land or the bottom of
water.

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