In order to control the rate at which voltage changes in the circuit, we must consider the values of the capacitor and resistor. In a circuit, the capacitor controls the voltage across its terminals depending upon how charged it is. The resistor limits the amount of current passing through the capacitor, which in turn affects the rate at which the capacitor charges.
Resistors are two-terminal devices that restrict, or resist, the flow of current. The larger the resistor, the less current can flow through it for a given voltage as demonstrated by Ohm's law. Electrons flowing through a resistor collide with material in the resistor body, and it is these collisions that cause electrical resistance.