Which example best represents an object with balanced forces acting upon it? a) a boat moving through the water. b) a book sitting on a high shelf. c) a wagon rolling down a steep hill. d) a baseball thrown thrown in the air.

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.