This applet provides an interactive simulation that allows one to gain both a qualitative and quantitative understanding of buoyant force. The definition of buoyant force is discussed. The user is able to select and change the density of the object and fluid, the drag coefficient (to allow for damping due to viscosity of the liquid), as well as the volume of the object, and then observe the corresponding results. The mass of the object changes automatically. The block may be placed at any position in the liquid and then released. This item displays (via colored arrows) the buoyant force, net force, mass, weight of displaced liquid, vectors representing the weight of the object, a graphical display of the displaced water, and a plot of position and velocity as a function of time for a period of about one minute. This item allows for feedback to the user for a wide variety of simulated experiments.
Type of Material:
A Java applet embedded in web page.
This material may be used as a demonstration, an in-class activity, pre-lab (for labs on buoyancy), or homework (with instructor provided assignments).
A Java enabled web browser and an internet connection are required.
Identify Major Learning Goals:
The user of this learning object will become familiar with relations between densities of objects, liquids, weight, and buoyant forces on the object. The learning object is helpful in displaying all the variables that effect the size of the buoyant force and whether an object will sink or float. The net force is calculated thereby allowing the user to spiral back to an application of Newton's 2nd Law.
Target Student Population:
Students enrolled in algebra or calculus-based college or college preparatory (i.e. high school) physics.
Prerequisite Knowledge or Skills:
A knowledge of mass, weight, force, volume, buoyancy, and density is helpful.
The calculated values of the weight, volume, and density seemed to be correct. The use of kg*w is helpful because it requires less calculations. The item displays all components needed for a detailed understanding of buoyancy at an introductory level. Users can play with the item to achieve equilibrium conditions for a wide range of values of densities. Feedback on conditions required for equilibrium are immediate since both forces and vectors are displayed. For more complicated situations users can observe the motion of the block as it approaches equilibrium or oscillates around it depending of the choices of initial conditions. The applet also displays x and y coordinates of the center of mass of the block.
The value of the velocity of the block as well as the drag force is not listed. Therefore it may be difficult to determine the exact value of the net force. The signs on the net force are reversed. The pause button does not seem to function unless the center of mass is above the equilibrium position. The use of units of "kg*w" for force should be explained. The "w" appears to stand for 9.8m/s^2, or equivalent in other units.
Potential Effectiveness as a Teaching Tool
The multiple displays of information is useful in helping the students gain a qualitative (i.e. conceptual) understanding of buoyant force. Much quantitative measurements can be made as well. This is a good control of variables exercise. The arrows that represent the weight of the block and buoyant force are displayed in real time. This helps the user to see how the buoyant force changes as more or less fluid is displaced while the weight remains the same. The net force is calculated as well. This enables the user to see how Newton's 2nd law applies in different situations. One can compare the direction or sign of the net force to the acceleration. Instructors should not have much difficulty developing some useful assignments for this item.
This applet contains no questions to provide the user with some direction. It may be good to just "play around" at first but eventually the instructor will need to develop some questions to assess the students knowledge of buoyant force. There are several variables that can be changed. The students need to know which ones to change and when to change them. Also, a little instruction on how to calculate the buoyant force and net force is needed. Limited precision on the placement of the block may not let the user obtain a position that is "exactly" at equilibrium.
Ease of Use for Both Students and Faculty
Each of the options provided is in itself very easy to use. Students will need to read the accompanying page to help familiarized themselves with this item. This will take about ten (10) minutes.
The RIGHT click feature does not work on Macintosh computers. Therefore it is difficult to change the volume of the block as well as resume a simulation once you have clicked 'pause'. Since there are many options and features to play with, users will need to take the time and read the instructions carefully.
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