“Sink or Float” Activity Notes Objective: Provide experience in formulating and testing hypotheses, classifying, and analyzing data.

–AN OBJECT’S DENSITY (DENSITY = MASS/VOLUME) DETERMINES WHETHER OR NOT IT WILL FLOAT. IF AN OBJECT’S DENSITY IS LESS THAN WATER, IT WILL FLOAT IN WATER; IF ITS DENSITY IS GREATER THAN WATER, IT WILL SINK.

–THE SAME PRINCIPLE OF DENSITY COVERED IN THIS LESSON APPLIES TO OBJECTS OTHER THAN SODA – HUMANS AND SHIPS, FOR EXAMPLE. PEOPLE WHO ARE VERY MUSCULAR AND HAVE A LOW PERCENTAGE OF BODY FAT FIND IT VERY DIFFICULT TO FLOAT, WHILE PEOPLE WHO HAVE A HIGHER FAT RATIO FIND IT EASIER TO FLOAT. THIS IS BECAUSE MUSCLE TISSUE IS DENSER THAN WATER, AND FAT TISSUE IS LESS DENSE THAN WATER.

ANSWER THIS QUESTION: IF METAL IS MORE DENSE THAN WATER, HOW CAN A HEAVY METAL SHIP FLOAT?

THE HEAVY METAL SHIP CAN FLOAT BECAUSE OF THE AIR PRESENT INSIDE THE SHIP. AIR HAS A DENSITY LESS THAN WATER, SO AIR IN A SHIP DECREASES THE SHIP’S AVERAGE DENSITY.

YOU CAN INCREASE THE ABILITY OF AN OBJECT TO FLOAT BY MAKING THE FLUID IT FLOATS IN DENSER. SALT WATER IS A GOOD EXAMPLE OF A DENSE FLUID. PEOPLE FIND IT EASIER TO FLOAT IN SALT WATER THAN IN FRESH WATER BECAUSE SALT WATER IS DENSER THAN FRESH WATER. SIMILARLY, SHIPS RISE WHEN THEY GO FROM FRESH WATER TO SALT WATER.