A bike is hanging from a hook in a garage. Consider the following forces:
(a) The force of the Earth pulling down on the bike,
(b) The force of the bike pulling up on the Earth,
(c) The force of the hook pulling up on the bike,
(d) The force of the hook pulling down on the ceiling.
Which two forces are equal and opposite because of Newton's third law? Which two forces are equal and opposite because of Newton's first law?