Energy, Work, and Conservation
Core ideas about work, kinetic and potential energy, and why energy is conserved.
Keyboard Shortcuts
💡 Pro tip: Use keyboard shortcuts for faster studying!
Study Smart Tips for Energy, Work, and Conservation
Master these concepts using proven study techniques that actually work:
Active Recall
Test yourself before flipping each card to strengthen memory retention
Spaced Repetition
Review difficult cards more frequently than easy ones
Multiple Sessions
Break study time into shorter, focused sessions
Explain Aloud
Verbalize answers to reinforce understanding
Questions Covered in This Set
10 cards to master
Work (definition and formula)
Energy transferred when a force moves something through a distance: W = F d cosθ, where θ is the angle between force and displacement.
Why does holding a heavy suitcase motionless do zero work on it?
There is no displacement, so d = 0 and W = 0. Your muscles burn chemical energy internally, but the suitcase gains none.
Why does gravity do no work on a horizontally carried bag — or on the orbiting Moon?
The force is perpendicular to the motion, and cos 90° = 0. That's why the Moon's orbital speed stays roughly constant.
Work–energy theorem
Net work done on an object equals its change in kinetic energy: W_net = ΔKE, with KE = ½mv².
Why does doubling your driving speed make a crash far worse?
Kinetic energy goes as v², so doubling speed quadruples the energy (and braking distance).
Conservative force
A force whose work depends only on start and end points, not the path (gravity, springs, electric attraction). These allow a potential energy to be defined.
Gravitational and spring potential energy formulas
PE = mgh near Earth's surface; PE = ½kx² for a spring.
What is chemical energy, really?
Electrical potential energy stored in the arrangement of electrons and nuclei — e.g. gasoline or ATP.
Conservation of mechanical energy
If only conservative forces act, KE + PE stays constant — which is why a roller coaster can never coast above its starting hill.
Noether's theorem and energy
Emmy Noether (1918) showed every continuous symmetry gives a conserved quantity: time-translation symmetry → energy, space-translation → momentum, rotation → angular momentum.
