2012_1061_Lecture_Ch_078

# A system not an object potential energy continued

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: WG = mg (y2 − y1 )  The gravitational potential energy, U is defined by Ugrav = mgy  Caveats: [gravity only] Change in potential energy is what is physically meaningful Potential energy belong to a system not an object Potential Energy (continued)  Potential Energy in General ∆U = −WG = − ￿ 2 1 − → − → FG · d ￿  There are other types of potential energies besides gravitational. We can define a potential energy only for conservative forces ∆U = U2 − U1 = − ￿ 1 2 −− →→ F · d ￿ = −W Elastic Potential Energy Fp = +kx Force of a person pushing Fs = −kx ∆U = U (x) − U (0) = − ￿ 1 2 Force of the spring pushing back − → − → Fs · d ￿ = − 12 Uel (x) = kx 2 ￿ x 0 12 (−kx)dx = kx 2 [elastic spring] Mechanical Energy and Its Conservation  Consider a conservative system( where only conservative forces do work) in which energy is transformed from kinetic to potential and vice versa ➥ Mass at the end of a spring ➥ Mass moving in the Earth gravitational ﬁeld  According to the work-Energy principle ∆Utotal Wnet = ∆K ￿2 − →...
View Full Document

Ask a homework question - tutors are online