1. The bubble machine in turn opens the lid of the drain.

2. Take out the water bottle and unscrew the lid.

3. Put the water in and screw on the lid.

4. Cover the back cover. Turn on the switch of the bubble machine to produce bubbles.

Bubbles are formed by the surface tension of water. This tension is the mutual traction force that exists inside the object and is perpendicular to the contact surface of two adjacent parts when the object is under tension. The mutual attraction between water molecules on the water surface is stronger than that between water molecules and air. These water molecules seem to be stuck together. However, if water molecules are excessively bonded together, bubbles are not easy to form. Soap "breaks" the surface tension of water. It reduces the surface tension to only one third of that under normal conditions, which is the best tension required to blow bubbles.