Description
Every conservation-of-energy problem you’ll ever see boils down to one of two cases: energy stays constant, or it doesn’t — and leaks out as heat. This video works through both, from a clean no-friction comparison of two very different paths, to a friction problem where you have to go find the missing energy yourself.
✅ Apply conservation of mechanical energy (K + U = constant) to solve for unknown speeds, heights, or positions
✅ Apply ΔEmech = Wnc when nonconservative forces act within the system
✅ Describe how mechanical energy lost to friction is dissipated as thermal energy or sound
⏱️ Timestamps
0:00 – Hook: every energy problem is one of two cases
0:37 – Total energy vs. mechanical energy, revisited
1:02 – Case 1: Ki + Ui = Kf + Uf
1:14 – Worked example: same height, different paths and masses
2:08 – Comparing final mechanical energies (and catching a mistake live)
2:39 – Solving for final speed: mass cancels out
3:20 – Aside: energy vs. kinematics vs. impulse-momentum
4:15 – Case 2: ΔEmech = Wnc
4:43 – Where the lost energy actually goes
4:54 – Worked example: energy dissipated by friction (pulley system)
6:23 – Solving: mgh − mv²
6:53 – A second way to check your answer: the total energy equation
7:30 – Worked example: a cart, a spring, and friction
8:56 – Frictionless prediction: x = 0.3 m
9:44 – Actual energy dissipated: 7.56 J
10:19 – Big picture: the two equations that cover this whole unit
This video is part of the MasteryFlip approach to AP Physics C — watch, take notes, then come to class ready to work problems together. Curious about the MasteryFlip Framework? Check out the ReachEveryStudent Podcast, new episodes every Monday at reacheverystudent.com.