Lesson 6 of 10 · 11 min
Conservation of mechanical energy
NCERT § "The Conservation of Mechanical Energy"
The coconut finally falls. Halfway down it has swapped exactly half its stored energy for motion. At the fair's slide, though, a child arrives at the bottom slower than the same drop should allow. Where did the missing energy go?
The lesson in notes
In short
If only conservative forces do work on a body, its total mechanical energy K + V stays constant.
A body falling freely from height H has the same total energy mgH at every point: potential energy turns into kinetic energy as it falls.
Speed at the bottom of a smooth curved track depends only on the height dropped, v = √(2gh), not on the shape of the track.
For a bob whirled in a vertical circle on a string of length L, the minimum speed at the lowest point for completing the circle is √(5gL), and the minimum speed at the top is √(gL).
When non-conservative forces like friction act, the loss in mechanical energy equals the work done against them: (K + V)_initial − (K + V)_final = work done against friction.
The energy lost to friction is not destroyed; it appears mainly as heat, so total energy is still conserved.