Lesson 17
Kinetic and Potential Energy
Learners discover that energy is not mysterious or invisible in the way we might imagine. Through hands-on demos with rubber bands, balloons, ramps, and pendulums, students see energy in action and learn to distinguish between two forms it takes: kinetic energy, which is actively doing something right now, and potential energy, which is stored and waiting to be released. The lesson builds toward two foundational rules of science: energy must be put in before it can come out, and energy cannot be created from nothing.


Key Ideas
  • Kinetic energy is energy that is actively doing something: motion, heat, light, and sound are all kinetic.
  • Potential energy is stored energy waiting to be released. A stretched rubber band, a ball at the top of a ramp, and a wound-up spring all have potential energy.
  • Energy constantly converts between kinetic and potential forms. In a swinging pendulum, the energy is fully potential at the top of the swing and fully kinetic at the bottom.
  • For energy to come out of a system, energy must first go in. Every hands-on demo in this lesson required the student to put energy in first.
  • Energy cannot be created. A roller coaster's first hill is always its tallest because the coaster can never gain more energy than it started with.
  • Energy and matter are completely separate things. Adding or releasing energy from an object does not change the object's weight.

Vocabulary
  • Kinetic Energy: Energy that is actively doing something right now. Motion, heat, light, and sound are all forms of kinetic energy.
  • Potential Energy: Stored energy waiting to be released. Found in a stretched rubber band, a raised weight, a wound spring, or compressed air.
  • System: A group of parts working together. Energy moves into, through, and out of systems.

Supplies for Live Class (all helpful, but optional) 
  • Ramp (any flat surface on an angle, a book balanced on other books works!)
  • Balls or toys to roll or slide down the ramp
  • Pendulum (a weight on a string tied to the edge of a table)
  • Balloon
  • Rubber bands
  • Spring-powered toy/wind up toy


Hands-On Activity: The Pendulum Energy Exchange

Supply List
  • A piece of string, approximately 18 to 24 inches long
  • A small weight (a metal washer, a heavy nut, or a small rock tied securely)
  • A ruler or tape measure
  • A fixed point to hang the pendulum from (a doorframe, a curtain rod, or a dowel held between two chairs)
  • A notebook and pencil


Instructions
  • Tie the weight securely to one end of the string. Attach the other end to a fixed point so the weight hangs freely.
  • Pull the weight to the side, about 6 inches from center. Hold it still for a moment and notice: the pendulum is not moving. Ask: is there energy in the system right now? How do you know?
  • Release the weight and observe. Count how many swings it takes before it clearly begins to lose height.
  • Mark with your finger where the pendulum rises to on each side after every three swings. Notice that it never rises higher than where it started. Discuss why.
  • Pull the weight to a wider angle and release again. What changes? What stays the same?
  • In your notebook, draw and label the pendulum at three positions: top of the swing (left), bottom of the swing, and top of the swing (right). Label where kinetic energy is greatest and where potential energy is greatest.

Sources

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L17: Kinetic and Potential Energy by Selene
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