Bubble solution: A mixture of liquid soap and water that we use to blow bubbles.
Gas: A substance like air that has no shape of its own but instead spreads out to take the shape of its container. The air inside a bubble is a gas. (For older participants: Gas presses equally on the thin skin of the bubble solution and makes the bubble’s shape a sphere.)
Liquid: Something like water, juice, or milk that flows and takes the shape of a container. The bubble solution is a liquid.
Sphere: A three-dimensional shape that is round like a ball, not flat like a circle. A bubble is a sphere.