Unit 3: Work, Energy, and Power
Energy is a second way to solve motion problems. Instead of tracking forces and accelerations moment by moment, you compare a system before and after: how much energy it had, how much was transferred in or out, and how fast.
What you will master
- Find the kinetic energy of a moving object: K = ½ m v², a scalar that is never negative.
- Find the work done by a force along a displacement: W = F d cos θ, and know when it is positive, negative or zero.
- Use gravitational potential energy near Earth (U = m g h) and spring potential energy (U = ½ k x²), and choose a zero level.
- Apply conservation of energy to a system, including energy transferred by work from outside and energy turned into internal (thermal) energy by friction.
- Find power as the rate of energy transfer: P = W / t, and P = F v for a constant force along the motion.
Rule used on every page: say what is in the system first. Energy is conserved for the system; work by outside forces is how it changes.
Topics
Do them in order. Each one follows the same path: story, idea, play, worked examples, practice, common mistakes. Then play the games and finish with the practice set.
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How this unit connects
Builds on Unit 1 (speed and displacement) and Unit 2 (forces). Many Unit 1 problems, like the speed at the bottom of a ramp, are faster with energy. Unit 4 adds momentum, the other conserved quantity, and Unit 6 adds the energy of spinning objects.