 Here I have a container with some water, a table tennis ball, a 5 rupee coin, a rubber band, a leaf and an iron nail. And one by one I'm gonna place these items in this container of water and I want you to observe what happens. So let's start with the table tennis ball. Okay, there you go. Now let's put this rubber band. Okay, now let's put this 5 rupee coin, the leaf and an iron nail. So what do we observe? We observe there's some objects float while some sink in water. The rubber band, ball and the leaf are floating and the iron nail and the coin sank. So this is also a way of grouping substances. We can group substances or objects on the basis of whether they float or sink in water.