Head back to the orphanage and enter it, then go into the door marked "Intro to Physics" to be confronted with your next riddle. Your goal is to guide an electrical charge through a series of pipes to the switch on the floor below you. The only problem is that the pipes aren't connected all the way from the beginning to the switch. You will be required to step on pads on the ground to raise and lower the remaining pieces of pipe, but they do so according to whoever is standing on them, as they are weight sensitive.
To begin with, have Batman stand on the pad on the far left, then place Catwoman on the middle one. Switch back to Batman and hit the switch (the question mark) to start the current. Once it passes the first tube, have Batman step off of the left pad and stand on the right one, then do the same with Catwoman after it passes through the middle. The current will then go up through the third tube and when it does, have Batman stand off of it and onto the middle one.
When it passes through Catwoman's, go and make her stand on the left pad, then do the same with Batman after it passes through his. This will make the current hit the switch and raise a platform on the floor below, but you will notice the entire floor is electrified. Have either of the characters stand on that raised platform, while the other steps down onto the floor below, which causes some of Riddler's robots to show up. You'll notice that some of them are red, while the others are blue. The red ones can only be defeated by Catwoman, while the blue ones are Batman's. You can change characters with L1 (the other will go to the pad to disable the electrified floor) to defeat them all. Collect the key after you're finished to complete the riddle.
