Answer:
attrition.
Explanation:
Attrition is a type of force that is present when two surfaces come into contact. An example of this can be seen when rocks carried by a river break and break into smaller pieces, this is because the river causes contact between the rock surfaces that eventually tear them apart and cause them to break. The surfaces of these rocks come into contact because the river causes one rock to bump into the other rock, thus generating friction between them, causing attrition.
