Explain brownian movement

When you view a sol through an ultra microscope, you will observe that colloidal particles appear to be in a state of rapid and irregular motion called the brownian movement. You may recall reading about the Brownian movement earlier under the properties of colloids.  The movement is  caused by the constant bombardment of the dispersed particles by the molecules of the dispersion medium.  The smaller the size of the colloidal particles, the more vigorous is its Brownian motion.