Mechanical Equivalent of Heat E-practical
A realistic 3D virtual physics experiment
This experiment shows the equivalence of heat and mechanical energy using a similar method to that of Joule.
Realistic experimental technique
Operate the apparatus yourself, make measurements and collect your own data. The experiment can be done badly, just like the real experiment, so the quality of the result depends on the care taken.
Useful when laboratory access is limited
IE-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.
Watch 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 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.
School/Department licence £9.99
Valid for 1 year
Introduction
It may seem that heat energy and mechanical energy are the same thing. But it wasn’t always so. In the middle of the 19th Century Joules experiment that measured this equivalence was ground-breaking and used state of the art thermometers to measure the tiny differences in temperature obtained. Indeed, it is not entirely clear how Joule made such accurate measurements. His thermometer (built by Henri Victor Regnault) had ten divisions per degree Fahrenheit and each of these divisions measures 0.5”. So, one division was equivalent to 0.1ᵒF Joule claimed that he could quite easily measure to one twentieth of a division allowing him to measure to one two hundredth of a degree.
At this time the nature of heat was not fully understood, and heat was commonly attributed to a substance called caloric which could be taken away or added to anything that could be heated or cooled. For example, caloric plus ice made water.
Joule’s original apparatus used weights that fell driving a cord around an axle that in turn, rotated a set of paddles inside a container of water.
There was a handle enabling him to wind the weights back to the top so that the mechanical energy could be repeatedly applied.
The weight and the distance fallen allowed him to calculate the mechanical energy. Careful measurement of the temperature of the water and the volume of the water allowed him to calculate the energy gained.
Our apparatus is a rather simpler. We generate the heat by the friction between a cord and a brass cylinder as described in the next few slides.
What students do
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Notice that there is a thermometer in the room giving the room temperature.
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The handle can be turned simply by placing the mouse over the area taken by the handle. You need to position yourself so that you can see the readings on the thermometer. Note the number of turns counter on the top of the apparatus.
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In order to minimize the effects of this possible gain or loss of heat to the room, it is good practice to take the cylinder to a temperature that is the same amount above room temperature as it starts off below. In this way, the amount of heat gained by the cylinder from the room will be the same as that lost to the room.
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Turn the handle (this will probably take a few hundred turns) until the final temperature is the same amount above room temperature as it was below at the start.
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Note these temperatures and the number of turns needed. You can calculate ΔT from the difference in temperatures at the start and end of the turning. Note, take these reading immediately before you start turning and immediately at the end before the cylinder starts to lose heat to the room.
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The result is simply the ratio of W/Q which we showed how to calculate in the Physics section of the PowerPoint.
Want to experience an e-practical yourself?
Try our free Magnetic Field for a Coil e-practical.
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This section is adapted from material developed by Dr Robert Lucas and is related to the book High School and Undergraduate Physics Practicals, published by CRC Press.