Thea lifts the cardboard away, and there is a magnet taped under the ruler.

The cardboard is gone. A magnet is taped under the ruler, above the paperclip.

The magnet pulls the paperclip up through the cardboard and the air, without touching it.

The thread pulls the paperclip down, and Earth pulls it down too.

Two opposite forces are balanced when they are the same strength.

The pull up and the pulls down are balanced, so the paperclip hangs still.

The magnet pulls the paperclip up. The thread and Earth pull it down. The paperclip hangs still.