The statements that describe physical weathering are:
-
Two rocks hit against each other in a fast flowing stream and break apart - This describes a physical process where rocks are mechanically broken into smaller pieces due to abrasion.
-
Small rocks are pushed together when a mole digs an underground den - This also describes a physical process as it involves the mechanical movement and compaction of rocks without altering their chemical structure.
The other two statements refer to chemical weathering:
-
Oxygen and water change the composition of the minerals in a rock - This describes a chemical weathering process where the chemical composition of the rock is altered.
-
Mosses grow on rock and produce acids that wear away the rock over time - This indicates a biological weathering process that also contributes to chemical changes in the rock.
In summary, the statements that describe physical weathering are the first and third ones related to abrasion and mechanical movement.