Why can't I play different tempos with my two hands on the piano?

So,I am learning to play the piano,but I have difficulties with playing different tempos with each of my two hands(separated).For example,when I want to play b with the one,and some notes or chords with the other hand,and they are with different tempos or speeds,my hands start to play the same tempo or speed together.That annoys me a lot.Is that related with the hemispheres?If you have any advice of what should I do,please tell me it.