The discussion clarifies the concept of work in physics, specifically addressing the relationship between work, kinetic energy, and potential energy. Participants confirm that work is defined as the change in kinetic energy plus the change in potential energy, expressed mathematically as W = ΔK + ΔU. They emphasize that when lifting an object at constant velocity, the net work done is zero, as the work done by the lifting force is balanced by the work done against gravity. The conversation also highlights the importance of distinguishing between net work and work done by individual forces.
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guitarphysics said:Oh, net work :). That's the big thing here! So look, when you lift something upwards, you're doing work on it, right? BUT it's not changing in kinetic energy! How? Because gravity is doing work that is equal to yours but opposite in sign, so there is zero NET work done on the object, thus its kinetic energy won't change ;).
Doc Al said:Hyperphysics is not defining work via the change in kinetic energy, they are describing the work-energy principle. And, as guitarphysics points out, it is the net work on a particle (including all forces acting) that gives the change in kinetic energy.
It's the net work that gives the change in KE. Of course, if only one force acts then the work it does will equal the change in KE, since that is the net force.dragon-kazooie said:So, you're saying that work is equal to Δk or -ΔU, but net work is only equal to Δk? (Because in the crane example, there's still a change in potential energy, even though there's no change in kinetic energy and no net work.) That seems really weird.