A hypothesis is an educated prediction that can be tested.
Not totally sure but i would say a normal? its not refraction or incidence if its perpendicular and i dont think its a mirror if its an imaginary line so yeah normal (normals are always perpendicular to their surface too i think so)
I think that the oceanic water particles mainly move in circles greater in the oceans surface because of how big the waves can be and how wind and air impact the motion. The water particles move more on the surface because of the other factors that impact it such as people, wind, air, etc...
The centripetal force acts upon an object moving in a circle at constant speed. The centripetal force acts perpendicular to the direction of motion , the speed of object will remain constant.
In both magnitude and direction since acceleration is a vector quantity
