Physical Weathering Lesson: Definition, Examples & More

Lesson Overview

• What Is Physical Weathering?

Have you ever noticed cracks in sidewalks, rocks that crumble, or smooth stones by a riverbank? These are signs of physical weathering-a natural process that slowly changes the Earth's surface.

Rocks may seem strong and unbreakable, but over time, they can be broken down by natural forces like wind, water, and ice. So, let us learn how physical weathering works, what causes it, and why it's important in shaping our world.

What Is Physical Weathering?

Physical weathering, also called mechanical weathering, is the breaking down of rocks into smaller pieces without changing what the rock is made of. The rock stays the same type of material-it just becomes cracked, chipped, or broken.

This is different from chemical weathering, which changes the composition of the rock. Physical weathering only changes the size and shape, not the makeup.

Example:

• A big granite rock that cracks into smaller granite pieces is physical weathering.
  
• But if the granite changes into clay due to chemical reactions, that's chemical weathering.

What Causes Physical Weathering?

Several natural agents cause physical weathering. These include:

Each of these forces works slowly over time. Together, they shape landscapes, carve out valleys, and even form soil.

Take This Quiz:

Weathering Quiz Questions and Answers

How Physical Weathering Happens: Key Processes

Let's look at some of the most common ways physical weathering occurs in nature:

a. Abrasion

When rocks rub against each other, they wear down. This happens when water, wind, or glaciers move rocks around.

• In rivers, rocks bump together and become smooth.
  
• In deserts, blowing sand polishes and breaks rocks.
  

b. Plant Growth

Tiny plant roots can grow into small cracks in rocks. As the roots grow thicker, they push the rock apart. Over time, the pressure causes the rock to split.

• Weeds on sidewalks are a great example of this!
  

c. Animal Action

Burrowing animals like moles, rabbits, and earthworms dig through soil and rocks. Their digging breaks rocks into smaller pieces and moves them around.

d. Frost Wedging (Ice Wedging)

In cold places, water enters cracks in rocks during the day. At night, the water freezes and expands, pushing the crack wider. Repeated freezing and thawing causes the rock to eventually split.

This process is especially common in mountains and cold climates.

How Gravity Contributes to Weathering

Gravity is the invisible force that pulls everything down. It plays a big role in physical weathering by:

• Causing rockfalls-when rocks fall from cliffs and break into smaller pieces
  
• Helping water flow downhill, which increases abrasion
  
• Creating landslides, where large amounts of rock and soil slide and shatter
  

Even without wind or water, gravity alone can break rocks simply by pulling them downward onto other surfaces.

What Affects the Rate of Physical Weathering?

Not all rocks weather at the same speed. The rate of weathering-how fast rocks break down-depends on several factors:

For example, limestone breaks down faster than granite, and coastal rocks weather quicker than those buried underground.

Physical vs. Chemical Weathering

It's easy to confuse these two types of weathering, but here's how they differ:

Both types often occur together, but physical weathering comes first-it increases surface area so chemical weathering can work faster.

Take This Quiz:

Science Quiz: Practice Questions On Physical Weathering!

Real-World Examples of Physical Weathering

The Grand Canyon

Formed by millions of years of physical weathering from the Colorado River and wind. The river's abrasion and the wind's force helped shape the deep canyon walls we see today.

Cracked Pavement in Winter

Water gets into small cracks in the road, freezes at night, and pushes the pavement apart. This repeated cycle creates potholes-just like it does in nature.

Mountain Boulders

Large rocks in the mountains often split due to frost wedging or pressure release. Temperature changes between day and night also cause expansion and contraction, which cracks rocks.

Smooth River Stones

Rocks in streams and rivers become rounded and smaller from constantly rubbing against each other and the streambed (abrasion).

Why Physical Weathering Matters

Though it happens slowly, physical weathering plays a huge role in Earth's systems:

• Helps create soil from rock
  
• Shapes landscapes like mountains, valleys, and cliffs
  
• Prepares rocks for chemical weathering
  
• Breaks down minerals used in farming and construction
  

Without it, Earth's surface would look very different-and natural processes like erosion wouldn't work the same.