Why does carbonated water, when poured into a cup, have bubbles?

Carbonated water is made by compressing, letting carbon dioxide (CO2) dissolve into a solution of sugar water or juice etc.. stored in a sealed bottle.

Why does carbonated water, when poured into a cup, have bubbles?
Soda.

Carbonated water is made by compressing, allowing carbon dioxide (CO2) to dissolve into a solution of sugar or fruit juice, etc., in a sealed bottle. Taking dissolved carbon dioxide into the water gives it a sour taste. That is carbonic acid water or soda water that people often say, also called cool drinks.

At room temperature, carbon dioxide is a gas. If you just pump it into the liquid, most of it won’t dissolve. When subjected to a certain pressure, carbon dioxide will be stably dissolved in water.

If the cap is opened, the pressure in the bottle decreases, the carbon dioxide rises and flies away, and immediately bubbles appear. Pouring carbonated water into the cup, we see bubbles for the same reason. If you stir the carbonated water in the cup a little, you will see a lot of foam increase.