hello friend, this is my first post please go easy on me. the best way i can express my problem is below. I attach a pic to give you a better idea. A is a circular disk with 4.5" diameter, DISK A is driven by C which is connected to a DC motor. B is a pin diameter of 1 mm which is gonna rotate in a uniform circular motion when DC motor is on. an object will be on each pin(B) which is hollow in the middle like a cylinder. if you can imagine everything i mention will be submerged to acid and i am trying to figure out what speed should i run the DC motor to keep the object always in-contact with pin B? density of acid say =x and density of object say =y is there any other factor i should consider? is it possible to use a formula to find out the velocity of motor. please help its not a home work, its a part of a mechatronic project where physics has nothing to do but because i came into a position where i need to find out the right speed i need physics :( thank you very much for your help.