Lesson Summary This lesson further explores displacement and relates it to buoyant force. By weighing objects while they are in water, students discover that because of buoyant force, objects seem to weigh less while they are submerged. Objects that float appear to weigh nothing at all. Students predict and measure the change in apparent weight of objects when they are submerged. Students will weigh an object outside of water, partially submerged, and submerged in water, and will compare the results on a graph.  Teacher Background When the object is submerged in water, it appears to weigh less than it does when it is out of the water. However, the weight of the object remains constant.  The weight appears to change in water because the buoyant force of the water pushing upward on the object counteracts the downward force of its weight. The buoyant force of an object is directly related to the amount of water the object displaces. For example, because the cylinders displace the same amount of liquid, the buoyant force on them is also the same.  This means that each of the cylinders appear to loose the same amount of weight when submerged. Several of the cylinders will float and appear to weigh nothing when in water.  This observation leads students to question whether the objects weigh nothing or whether some other explanation might better describe the situation. Set-up/Management Tips If water has been saved in containers, it can be reused for this investigation. Set up multiple testing stations. Literacy Support Scientific Vocabulary The following words are key vocabulary words that will be introduced in this lesson and reinforced throughout the unit: Continue to use vocabulary introduced in previous lessons.