Our Sinking, Floating, and Hanging Concept Builder targets student understanding of the details that cause an object to sink to the bottom of its container, to float on the top of the water's surface, or to hang amid the water in neutral buoyancy. There are three independent activities in the Concept Builder. We have ordered the activities such that the one requiring calculations comes last. We imagine that the third activity might work out best as the first activity for many students who are comfortable with the mathematics. In all three activities, students will have to relate the force of gravity to the object mass. And they will have to relate the buoyant force to the volume of water displaced. They will need to know that sinking results when there is insufficient buoyant force to balance the force of gravity and that floating results in situations in which a fully submerged object encounters more buoyant force than the force of gravity.

In the first activity, the analysis is done for two fully submerged objects. Mass and volume data are given for two objects. Students must compare their F_grav and F_buoyant values to one another. Then they must predict what would occur to each object after being released - sink to the bottom, rise to the surface and float, or "hang" right where it is at. The second activity provides information about the two objects. The information includes comments like "same volume", "same mass", "different shape", "in different aqueous environments" (pure vs. salty water), "different mass", etc. The diagrams show the objects resting on the containers bottom or floating at varying depths of immersion or hanging or held by a force beneath the surface or ... . Students must use the information to compare their F_grav and F_buoyant values to one another and to compare the average densities of the two objects. We use the term average densities since in some cases the objects are hollow cubes or hollow spheres or "boats" and the objects consists of a shell with enclosed air. The average density is the total mass divided by the total volume (shell + air). 

The third activity is the only activity involving calculations. The mass (or weight) and the volume of a single object is given. The object is fully submerged below water and then released. They must calculate the F_grav value and the F_buoyant value immediately after being released. They must identify the resulting free-body diagram from among 8 options. Attention must be given to the direction of the two forces and their relative magnitude. And then they must predict whether the released object will float to the surface, sink to the container's bottom, or hang in neutral buoyancy.

The Sinking, Floating, and Hanging Concept Builder is comprised of 72 questions. The questions are divided into 18 different question groups. Questions in the same group are rather similar to one another. The Concept Builder is coded to select at random a question from each group until a student is successful with that group of questions. The questions and question groups are organized into three different activities. The activities are differentiated as follows:

• Case Studies 1 Question Groups 1-6: Students are given the mass (or weight) and volume information of two objects that are submerged under water and released. They must compare the F_grav and the F_buoyant values and identify whether they will float, sink, or "hang" (achieve neutral buoyancy).
• Case Studies 2 Question Groups 7-12: Students are given two diagrams of different but similar objects (for instance, same mass and material but different shape) showing how they either float, sink, or hang. They must compare the F_grav and the F_buoyant values and identify which has the greatest average density.
• Force Analysis Question Groups 13-18: Students are given the mass (or weight) and volume of an object that is submerged under water and released. They must calculate the F_grav and the F_buoyant values, identify the correct free-body diagram at the moment of release, and then predict whether the object will float, sink, or "hang" (achieve neutral buoyancy).

Before using the Concept Builder with your classes, we recommend that teachers attempt each of the activities in order to determine which are most appropriate for your classes and what pre-requisite understanding a student must have in order to complete it. Alternatively, the Questions are provided in a separate file for preview purposes. 

In order to complete an activity, a student must correctly analyze each question in that activity. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the level. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the cue of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question in an activity has been analyzed, the student earns a Trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned activities.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each Question Group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise. 

 

 

We do not have a lot of resources on the topic of Fluids at The Physics Classroom website. Besides Concept Builders, we also have a large collection of CalcPad problem sets.