  Electromagnetic waves carry energy, linear momentum, and angular momentum.
When light (or other electromagnetic radiation) interacts with material media,
both energy and momentum are usually exchanged. The force and torque
experienced by material bodies in their interactions with the electromagnetic
field are such that the energy as well as the linear and angular momenta of the
overall system (i.e., the system of field plus matter) are conserved. Radiation
forces are now used routinely to trap and manipulate small objects such as
glass or plastic micro-beads and biological cells, to drive micro- and
nano-machines, and to contemplate interstellar travel with the aid of solar
sails. We discuss the properties of the electromagnetic field that enable such
wide-ranging applications.
