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Idea: In order to stretch a spring, it is necessary to do external work on the spring. This work is stored in the spring and is called the elastic potential energy ( PEs ). PEs depends on the spring constant, k , and the net displacement from equilibrium x and is given by:
PEs = kx 2. | (4) |
The elastic potential energy contributes to the total mechanical
energy of the harmonic oscillator:
E total | = | KE + PEs + PE grav | |
= | mv 2 + kx 2 + mgy | (5) |
In the absence of friction, the total mechanical energy is
conserved, i.e. it is constant throughout the motion. This is
expressed
graphically (for zero gravitational potential,
PE grav = 0 )
in Fig.13.1.
Idea: When a harmonic oscillator reaches its maximum displacement, x = A , it must turn around and go back. At this turning point, the velocity is zero, and the total mechanical energy can be written in terms of the amplitude ( PEgrav = 0 ):
E total = kA 2. | (6) |
v = . | (7) |
v max = . | (8) |
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