How does the total potential and kinetic energy vary with time?
Total mechanical energy should be constant. Total mechanical energy at any point = potential + kinetic Over time if potential energy increases then kinetic decreases (such as a ball moving upward — its gravitational potential energy is increasing and the kinetic energy is decreasing as it slows down) If potential energy decreases then kinetic energy increases (such as a book falling from a desk– the height is decreasing, so gravitational potential is decreasing, and the velocity is increasing, so the kinetic energy is increasing.) Note that we assume we have a closed system, so no energy is lost to non-conservative forces. That means we’re assuming there is no air resistance on the ball or the book. Once the book hits the floor the mechanical energy of the book will be transferred to other forms of energy.
