CONCEPTS AT A GLANCE The elastic potential energy is added to other energies to give the total mechanical energy, which is conserved if Wnc, the net work done by external nonconservative forces, is zero. As this bungee jumper oscillates up and down at the end of the elastic cord, the total mechanical energy remains constant, to the extent that the nonconservative forces of friction and air resistance are negligible. ( Terje Rakke/Stone/Getty Images)

Figure 10.18 CONCEPTS AT A GLANCE The elastic potential energy is added to other energies to give the total mechanical energy, which is conserved if W_nc, the net work done by external nonconservative forces, is zero. As this bungee jumper oscillates up and down at the end of the elastic cord, the total mechanical energy remains constant, to the extent that the nonconservative forces of friction and air resistance are negligible. (© Terje Rakke/Stone/Getty Images)