Classroom Activity
Sedimentary Sleuths Program
National Park Service
U.S. Department of the Interior
Acadia National Park
E XP E R IE N CE YO U R A M ER I CA ™
BACKGROUND INFORMATION
There are different types of weathering, as discussed in the water erosion activities of Sedimentary
Sleuths. The two main types of weathering are physical (also called mechanical) and chemical.
Physical weathering happens when rocks break down into smaller pieces. When water seeps into
the cracks in rocks and freezes and expands, it causes cracks to grow and rocks to break apart.
This is called freeze-thaw. Another example of physical weathering is when salt water gets into
cracks in rocks. After the water evaporates, the salt crystals left behind will expand and cause the
cracks to expand. Physical weathering does not change the composition of the rock.
Chemical weathering is different, because it does change the rock’s composition. Some of the more
common types of chemical weathering are dissolution, which is when acidic waters dissolve rocks,
and oxidation, when the iron in rocks becomes oxidized or “rusts”. In these experiments, you’ll get
to see examples of physical and chemical weathering in action.
1. Demonstrating the effects of physical weathering
MATERIALS
1 antacid tablet per student
1 small re-sealable plastic bag per student
1 durable object for crushing tablets per 4-5 students (rubber mallets, smooth palm-sized rocks, etc.)
Data sheet and pencil to record observations
PROCEDURE
1. Distribute 1 antacid tablet and 1 bag per student.
2. Have students record observations about antacid tablet before it undergoes any “weathering” processes.
Observations should include size, texture, and any other things they notice.
3. Place tablets in bags and close tightly with as little air inside as possible.
4. Using the durable objects, have students take turns to carefully crush the antacid tablet inside the bags.
5. Once they feel satisfied with their weathering, have students record their new observations on the data sheet.
RESULTS – The antacid tablet should have broken into small pieces after it was physically weathered by crushing it
into small pieces.
Physical and Chemical Weathering
