When we go out in the summer to enjoy the pools and the rivers, we always have to make sure that all of our equipment and safety measures are working and in place. When we go to the river and get on our boats, we make sure the boat has no leaks and we have our safety vests on. For young children who are still learning how to swim, we make sure they have their floaters on or we swim with them in a swim ring to make sure they do not sink. Why is it that boats and swim rings both float? There are many factors that determine if an object will sink or float in water, and one of these factors is what we call the specific gravity.

The specific gravity is the ratio between the density of an object, and a reference substance. The specific gravity can tell us, based on its value, if the object will sink or float in our reference substance. Usually our reference substance is water which always has a density of 1 gram per milliliter or 1 gram per cubic centimeter.