Density E-practical
Introduction
Density is simply how heavy something is per unit volume. As an equation it is simply mass divided by volume:
d = mass/volume = m/v
This will usually be expressed in kg per m^3 or sometimes as grams per cubic centimetre (gm/cm^3).
How do we get a precise result for the density? We answer this question with this experiment in two ways. If a body is regularly shaped, such as a cube or a sphere, then we can calculate its volume using geometry. If it is irregularly shaped then we need to be more cunning. Here we use the volume of water displaced when the body is submerged. In both cases finding the weight of a body is a simple matter of weighing it, and once we have the volume and the weight, the density is simply derived from the above formula.
Realistic experimental technique
E-practicals are 3d, highly realistic emulations based on a blend of theory and the actual practicals, giving an authentic experience of doing the actual practical in a laboratory. Students operate the apparatus, make measurements and obtain their own results. It is designed to reproduce the experience of performing the practical rather than simply demonstrating the underlying physics. Like a real experiment, it can be done badly. Careless setup or measurements can produce poor results, so students have to apply experimental technique and take care with their measurements.
Works directly in a browser
No installation is required. Windows, Mac and suitable mobile devices can run the WebGL e-practical.
See it in Action
This shows how the e-practical can be used. In particular it shows how the student or teacher interacts with the apparatus and how the interaction can be controlled using the mouse or the alternative on-screen controls.
What students do
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For the regularly shaped object, such as a cube, measure its weight using the scales. Use a ruler to measure its length and calculate the volume.
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Calculate the density using the formula for density given above
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For an irregularly shaped object, such as a pointer style knob, measure its weight using the scales.
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Then use how much water it displaces to determine its volume.
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This can be done by filling a large beaker with water to the brim and positioning a measuring flask to catch the water that overflows when the object is submerged into the water.
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The volume can then be read directly from the scale on the side of the measuring flask.
What you get
The application is supplied as a PowerPoint which provides background, a synopsis of what the student will learn, a description of the Physics involved, a description of the apparatus, the independent and dependent variables, the method, a link to the interactive online e-practical, analysis of the results and further discussion.
E-practical
Runs in a modern web browser. No software installation required. Recommended or desktops but will run successfully on tablets of medium to large size with a browser that supports WebGL.
School/Department licence £9.99
Valid for 1 year