A series of plastic tubes with various clear liquids and a ball as an indicator of viscosity.
People turn the tubes over and watch how long the balls take to drop through the liquids.
To see that a simple test can be used to compare things that differ. There are different grades of motor oil - we use a thicker grade in the summer when the temperature is higher because the ciscosity generally decreases as temperature rises. They are not the same. Oil is more viscous than water, but oil is less dense than water. Up to Exhibits home page.