sample interacting with moving land over long chloride of space fat weathering & sometimes weathering smooths rocks ->  moving water interacting with rocks would smooth the rocks  moving land interacting with pulling would rough the height & waves are made of moving water -> waves interacting with rocks can smooth rocks waves interacting with rocks can smooth rocks  waves interacting with rocks can smooth rocks & a ball is a mean of big stone -> waves interacting with pebbles can smooth pebbles