The discussion centers around the applicability of the Kinetic Work Energy Theorem, particularly in scenarios involving rigid and deformable bodies. Participants explore the definition of work and its relationship to energy changes, including potential energy, and question the generality of the theorem in various contexts.
Participants express differing views on the applicability of the Kinetic Work Energy Theorem, particularly regarding its limitations with deformable bodies and the definition of work. The discussion remains unresolved with multiple competing perspectives presented.
Participants highlight the dependence on definitions of work and energy, and the discussion includes unresolved assumptions about the nature of forces acting on objects and their effects on energy changes.
uestions said:When does the Kinetic Work Energy Theorem not apply to a situation?
uestions said:is there a general form of the equation where work can equal the change in any energy?
uestions said:What is work besides a force and a distance?
Here's something that I wrote in another thread that may clarify how the "work"-energy theorem, when thought of as an application of Newton's 2nd law, may be applied to deformable bodies.TysonM8 said:The Work-Energy Theorem only applies to rigid bodies. That is, if the work is not used to deform the object.
Doc Al said:The so-called 'work'-Energy theorem is really an application of Newton's 2nd law, not a statement about work in general. Only in the special case of a point mass (or rigid body) is that "work" term really a work (in the conservation of energy sense).
If you take a net force acting on an object (like friction) and multiply it by the displacement of the object's center of mass, you get a quantity that looks like a work term but is better called pseudowork (or "center of mass" work)--what it determines is not the real work done on the object, but the change in the KE of the center of mass of the object. This is usually called the "Work-Energy" theorem:
F_{net}\Delta x_{cm}=\Delta (\frac{1}{2}m v_{cm}^2)
Despite the name, this is really a consequence of Newton's 2nd law, not a statement of energy conservation.
If the velocity doesn't change, the work-kinetic energy theorem just says that the net work must be zero. You do work when you lift an object at constant speed, but gravity is also doing negative work.uestions said:How can work be done to an object that has a change in potential energy, but no change in velocity?