Assessed Understandings

8thGrade Transformation of Energy

  1. Energy can be sorted into a variety of forms including gravitational potential energy (GPE), kinetic energy (KE), heat energy, and electromagnetic energy. Mechanical energy is the sum of both gravitational potential energy and kinetic energy. GPE depends upon the object’s mass and height above the ground; KE depends upon the object’s mass and speed.
  2. Energy is not easily defined, so it is characterized by the change that is produced because of the flow of energy. Energy can be passed from one object to another (energy transfer) and changed from one form to another (transformation). Forces are responsible for the transfer and transformation of energy. In order to understand many systems, it is important to trace the flow of energy. Energy chains can be used to show the flow of energy in a system.
  3. Different materials transfer energy at different rates (characteristic of the material) and respond differently to the input of different forms of energy (i.e., selective absorption of electromagnetic energy). The rate of transfer of heat energy depends upon the substance’s temperature, its mass, and the contact time. All substances will interact thermally when placed together (particles of each substance will collide and transfer energy) until they reach a common temperature (thermal equilibrium).
  4. Heat energy is defined as the random, disorganized KE of particles. Temperature is a measure of the average KE of these particles, whereas heat energy refers to the total energy of all of the particles. Temperature is related to the concentration of heat energy, and not the amount of heat energy.
  5. Heat energy can be moved in three ways: conduction, convection, and radiation. In conduction, the particles vibrate and transfer energy by way of collisions between the particles that make up the substance. In convection, the particles still vibrate randomly, but transfer their energy through organized motion (convective currents) in the substance, producing a much more efficient form of energy transfer. In radiation, the heat energy is actually transformed into electromagnetic energy and transferred by way of an electromagnetic wave.
  6. Waves transfer energy, not mass. Waves can be characterized by wave speed, frequency, wavelength, and amplitude. Waves separate into two distinct categories dependent upon their pattern of vibration. Compressional waves (or longitudinal waves) oscillate in the same direction as the direction of motion; longitudinal waves oscillate perpendicular to the direction of motion. When waves interact with materials, the wave may be reflected from the material, absorbed by the material, or transmitted through the material.
  7. Mechanical waves are caused by highly organized vibrations of the particles that make up substances; a certain range of vibrations activate human hearing and is interpreted by the brain as sound. Electromagnetic waves are caused by vibrations in electric and magnetic fields. A certain range of these vibrations activate the human eye and is interpreted as visible light. Heat energy is often contrasted with the energy transferred by waves in that heat energy is the disorganized/random movement of particles that transfers energy, while waves are the highly organized movement of particles that transfers energy.

© 2010 Delaware Department of Education1