If the mass of the cylinder is infinitely zero, wouldn't the velocity of the cylinder be infinitely large? It seems to me that this would be a physically impossible situation. During the change in volume, this force does work, w. When your piston expands it reduces the atmosphere volume as a whole from $V_$)seems to have nowhere to go but the kinetic energy of the cylinder. The pressure, p, acting on the surface of the piston produces a force, F. The only problem consists in the fact that you consider that the atmospheric pressure will remain constant. Of course, if the expansion is done reversibly (say, by imposing a very gradually varying external force on the gas within the cylinder), the work can be calculated using the ideal gas law to determine the force on the inner piston face, since, in that case, viscous stresses and non-uniformities within the gas are negligible. We are thereby able to more easily calculate the amount of work done by the gas on the surroundings. So, whereas, the knowledge of the internal force on the piston requires solution of the partial differential equations for aerodynamics, for textbook thermodynamics problems, we usually assume that we can impose the external load precisely. However, we typically assume that we have better control over what is happening with the external load (such as through feedback control systems, or by having a vacuum outside and using a piston with mass). So, without solving the partial differential equations for aerodynamics, we have very little knowledge of the force on the inner piston face.Īlso, as safesphere points out, if there is a gas present (like the atmosphere) external to the piston and cylinder, analogous effects can occur within this gas. Secondly, a gas experiencing a rapid deformation does not obey the ideal gas law even locally there are viscous stresses in the gas (proportional to the rate of deformation) which contribute to the force at the inner piston face. Which of the following group have different dimensions (1) Potential difference, EMF, voltage (2) Pressure, stress, young's modulus (3) Heat, energy, work-done (4) Dipole moment, electric flux, electric field Practice questions, MCQs, Past Year Questions (PYQs), NCERT Questions, Question Bank, Class 11 and Class 12 Questions, NCERT Exemplar Questions and PDF Questions with answers, solutions. It is lower at the piston face than on average within the cylinder. Well, first of all, in a rapid irreversible expansion like this, the pressure of the gas within the cylinder is not uniform (spatially). Work done is equal to energy transferred.If you do a free body diagram on your massless, frictionless piston, you can only conclude that the force exerted by the gas on the inside face of then piston is equal to the external force exerted on the outside face of the piston. Specifically, a person could not push the box (and so do work) in the example above without energy. You do not have to do work if you have energy though (potential energy does not do work). This is because energy is the ability to do work. Work done has the same units as energy – joules. So the net work done in forcing the water through the pipe is V P. Similarly, if P P is the pressure at the outlet, the work the water does against the water ahead of it when exiting the pipe is ( P P) V. The triangle above may help you to rearrange the equation. If P is the pressure at the inlet, the work you need to do in forcing the water into the pipe is F d ( P A) × ( V / A) P V. In the example above, 10 N is applied to move the box 2 m. Here is the equation that relates work done, force applied, and distance moved in the direction of the force: What is the work done in each case As a reminder, W P dV, and pressure can (and does in many instances) depend on volume. A man pushes a box with a force of 10 newtons to move it a distance of 2 metres Calculating work done Whenever work is done, energy is transferred from one place to another. Work is done whenever a force moves something.Įveryday examples of work include walking up stairs, lifting heavy objects, pulling a sledge and pushing a shopping trolley.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |