Define speed and velocity.

When you push downward on a book at rest on a table, you feel an upward force. does this force depend on friction? defend your answer.

What are the necessary conditions for fusion?

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.