After you learn how momentum is conserved between portals, you reach Test Chamber 11.
Watch the Portals
There is another pit full of poison here, so be careful not to fall in. As you go forward, you will see a portal gun through the window that is creating orange portals. Watch it and you will see it make portals above the poison floor, and then it will make a portal beneath where you can see. Create a blue portal on the wall and look through it, and you will see that when it creates a portal where you can see, the portal leads to a safe platform. Go through the blue portal then.
Push the Button
Watch the on-screen display when you are near the button, and it will tell you how to press it. This will temporarily open a door in the wall to a different part of the chamber. Create a blue portal beyond this door, then wait for the rotating portal gun to create an orange portal in your area, and go through.
High Energy Pellet
Wait for the rotating portal gun to make a portal on the wall where the pellet containment machine is shining an orange light on the wall. Then shoot a blue portal onto the wall where the high energy pellet has left a dark mark. When the pellet enters the containment machine, the Unstationary Scaffold will start moving.
Get the Portal Gun
Make a blue portal where you will be able to walk through it, then wait for the rotating portal gun to create a portal on the wall where the Unstationary Scaffold stops. Look through your blue portal, then step through when the Scaffold has stopped there. It will take you to the rotating portal gun, which will upgrade your gun to create both orange and blue portals.
Push a Second Button
Press the red button that appears. It will open the door on the wall above. While it's open, create a portal of either color on the wall beyond the temporarily opened door. Then create a portal of the other color on the wall where the Unstationary Scaffold will go. Step onto the scaffold and go through the portal. You can now go into the elevator to Test Chamber 12.