Which statement describes the motion of a mass on a spring? a. it exhibits constant velocity motion. b. it exhibits simple harmonic motion. c. it exhibits circular motion. d. it exhibits only upward motion.

Which of the following is part of the explanation or description of electromagnetic waves? (select all that apply) a. electrically charged molecules in a medium transfer their energy to nearby electrically charged molecules. b. a changing electric field causes a changing magnetic field. c. magnetic molecules in a medium transfer their energy to nearby magnetic molecules. d. a changing magnetic field causes a changing electric field.