What is Conservative and non-conservative forces?

Example 29.4 (Two trails to the hut)

A $75\,\mathrm{kg}$ hiker gains $300\,\mathrm{m}$ by a steep $800\,\mathrm{m}$ trail or $2.4\,\mathrm{km}$ of switchbacks. The weight charges $-75 \times 9.81 \times 300 \approx -2.2 \times 10^{5}\,\mathrm{J}$ on both; a $30\,\mathrm{N}$ friction force, $-2.4 \times 10^{4}\,\mathrm{J}$ on one, $-7.2 \times 10^{4}\,\mathrm{J}$ on the other. The weight refunds on the descent; friction’s bill is gone as heat, both ways.

Example 29.10 (The pendulum, honestly this time)

A pendulum bob on a wire of length $L = 2.5\,\mathrm{m}$ is released at rest at $45{}^{\circ}$ from the vertical. The tension, perpendicular to the motion, is powerless; the weight is conservative: $E_m$ is conserved on the curved arc, which last year could only be checked. The bob starts $h = L(1 - \cos45{}^{\circ}) = 0.73\,\mathrm{m}$ up, so at the bottom $v = \sqrt{2gh} \approx 3.8\,\mathrm{m}/\mathrm{s}$.