Liquid water, ice, and water vapor are all the same substance, but they have different physical properties. That’s because they are all different states of the same substance. A solid feels firm when you touch it because the particles that make it up are packed closely together. You can move your fingers through a liquid. The particles of a liquid move freely enough to slide past one another. The particles of a gas are the farthest apart and move the fastest. Bubbles of carbon dioxide gas are lighter than the liquid in the glass, so they float to the top and escape into the air.