If you add an extra bulb to your series circuit what will happen to the brightness of your bulbs?

They will dim because you have more resistance in the circuit. More resistance means less current which means less light. The power is P=V*I = I/R*I = I²/R

Think of blowing through one straw. Now attach a second straw end on with no leaks between joints and then attach a third straw in a long line. Which one is the easiest to blow?