Why isn't the 2 ohm in the first equation negative? Since it's traveling along the current direction (it's clockwise), I don't understand why we are adding it.
Actually, we are travelling around the loop clockwise (as indicated by the blue arrow), but we are saying that the current is flowing counterclockwise (the red arrow called I1). Therefore, we have a voltage rise across the resistor and it's a positive 2 ohms.
The voltage rises and drops are in accordance with the assumed current path that we decide, not the actual current flow from + to - terminals.
Hey Ariel,
Actually, we are travelling around the loop clockwise (as indicated by the blue arrow), but we are saying that the current is flowing counterclockwise (the red arrow called I1). Therefore, we have a voltage rise across the resistor and it's a positive 2 ohms.