Brake question

Ok stupid question but here it goes.

How do you know if its your brake pads or rotors?

I have been noticing that when i stop lately once i get to the point that i am going rather slow i feel a slight jerk forward every few seconds.

its sort of like when you are pulling a pallet jack and something gets stuck in the wheel < sorry the best way i know to describe it> every few seconds theres a bump.

Thought it may be the pads but no squeak or scrape noise.
Dont want to buy something i dont need ya know

a pullsation would be the way I would describe a warped rotor.
Usually when you hit the brakes not only can you feel the car pullsate but you should feel it in the peddel as well, a bouncing type feeling. Not always but sometimes.
If this is the case, pads and rotors are what you want to replace.