1. What is mechanical weathering?
By. Mr. White
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2. Learning Objective
Students will explain the ways that Earth's surface is worn away by mechanical weathering.
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3. Key Terms
weathering
chemical weathering
mechanical weathering
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4. Weathering
The breaking down of rocks and other materials on Earth's surface is called weathering.
Newly made bricks are bright red.
They have sharp comers and edges.
Old bricks are darker red.
They have rounded comers and edges.
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5. Kinds of Weathering There are two kinds of weathering.
Chemical weathering occurs when the chemical makeup of the rocks changes. The sizes and shapes of the rocks may also change.
Mechanical weathering involves only physical changes, such as size and shape. The chemical makeup of the rocks does not change.
Mechanical weathering occurs as a result of temperature changes, ice wedging, and root action.
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6. Temperature Changes Heat makes things expand, or become larger.
Cooling makes things contract, or become smaller.
During the day, heat can cause the outside of a rock to expand.
At night, the outside of the rock cools and contracts.
The repeated heating and cooling of the rock's surface each day may cause pieces of it to flake or peel off.
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7. Ice Wedging Water enters cracks in rocks.
When the temperature drops below freezing, water freezes and expands.
The expanding water is like a wedge, making the crack wider.
After the repeated freezing and melting of water, the rock breaks apart.
Potholes in streets are caused by ice wedging.
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8. Over long periods of time, weathering changes the shape of mountains
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9. Root Action
Plant roots in search of minerals and water can grow into cracks in rocks.
Tree roots may cause cracks in sidewalks by lifting up the sidewalk.
The pressure of the growing root can make the cracks in rocks larger.
As the roots grow, they can break the rocks apart.
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10. Growing plant roots can lift up sidewalks
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11. Checking Concepts
Is breaking a rock into pieces chemical or mechanical weathering?
What kind of weathering causes potholes?
Does root action cause mechanical or chemical weathering?
What kind of weathering do changes in temperature cause?
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12. Answers
Mechanical weathering
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13. The End