Although air is treated as a uniform gas, its major component is nitrogen 5. Because molecules are free to move about, they fill any container, regardless of shape or size. The size of the gas molecules is very small compared to the distance between the molecules. The motion of gas molecules is constant and random. A gas is an example of a fluid.
Liquids are also fluids.
Obtain two beakers and fill them with water. Carefully add a dropper of dye or food coloring to the top of the water. Forcefully squirt a dropper of dye or food color into the second beaker of water and describe the process you observe. A force was added from the dropper. If you now stir the dye around in a circular motion in the beaker, you should see rotational motion.