most of the earth is covered with oceans
 
        
                    
             
        
        
        
I think the answer is periodic motion.
        
             
        
        
        
Answer: Gravitational potential energy changes.
Explanation: This is because depending on the amount of mass in an object that’s the amount of gravity pulling you down to the center of the earth
 
        
             
        
        
        
It can be observed without changing the identity of the object.
        
             
        
        
        
You need to attach the answer choices