Lesson Summary Students begin their investigation of buoyancy, the tendency of an object to float, by making and testing predictions about the variety of objects they have collected.  This experience will give students a chance to become familiar with the process they will use throughout the unit: predicting whether objects will float or sink, explaining why they think so, and testing their predictions. As students go through this process and explain their reasoning, you will gain insights into their ideas about floating and sinking. Teacher Background Two of the characteristics that affect floating and sinking are easily measured—the weight and the size of objects. For instance, a ship doesn’t float “because it is light”; rather, it floats because its weight and size act together so that the water (or other liquid it is floating in) pushes up on the ship with a force equal to the force of gravity pulling down on it. The upward push of the water depends on the amount of space the ship occupies under water, and it is called the buoyant force. Set-up/Management Tips Teachers should have a bag of objects children could use, in case they leave their objects at home the day of testing.  Set up multiple testing stations. If interested in reusing the water for future lessons, the water can be stored in gallon containers in the classroom. Literacy Support Scientific Vocabulary The following words are key vocabulary words that will be introduced in this lesson and reinforced throughout the unit: Buoyant Force Floating Force Force