On the Physics of Work
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- Published: Monday, 06 September 2021 09:00
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Happy Labor Day to all in the US!
(and belated greetings to readers elsewhere for whom Labor Day was in May.)
This holiday celebrates all kinds of work, but in physics Work is a more specific and mathematically defined quantity Today we’re taking a look at a couple of recent articles in The Physics Teacher that related to the concept of work in the classroom.
In physics, work is the energy transferred to or from a body via the application of force over a distance. Positive work is work done in the direction of motion, negative work is done in the opposing direction (or has components in those directions, in a 3-dimensional system). We sometimes, conversely, refer to energy as the ability to do work.
A recent paper in The Physics Teacher by G. Planinšič & E. Etkina, “Boiling water by doing work” (https://doi.org/10.1119/5.0049411), shows some of this relationship between work and energy. As work is done on a system, moving a rope, some of the energy in the system is dispersed as heat. This heat is then seen to boil water. In their videos (linked in the article), you can see the relationship between work done on the system and temperature, and calculate for yourself the efficiency of energy conversion.
A paper in The Physics Teacher last year by P. Gash looks at potential energy and work in a more familiar mechanical system: a Slinky. In “A Slinky’s Elastic Potential Energy” (https://doi.org/10.1119/1.5145416), we can see a detailed breakdown of the forces acting on the coils of a Slinky. You can check out the experimental data for yourself and calculate the work done by gravity on the spring. It’s a handy reminder that work in the physics sense doesn’t always mean human labor!
We have many demonstrations in our collection relating to physical work. Section C8 of our demonstration index is all about the mechanics of energy, power, and work; all are useful in the classroom, and many can be tried at home as well with materials you have on hand! There are many other demonstrations that explore energy and work as well, from thermodynamics experiments like the one in the paper above, to the newly repaired J4-31: Energy Stored in a Capacitor, which shows a capacitor that holds enough energy to let a motor do the work of lifting the capacitor itself against gravity. Now that’s a nice bit of work!
