instruction:
In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
question:
What determines the model of forces?, Context: For certain physical scenarios, it is impossible to model forces as being due to gradient of potentials. This is often due to macrophysical considerations that yield forces as arising from a macroscopic statistical average of microstates. For example, friction is caused by the gradients of numerous electrostatic potentials between the atoms, but manifests as a force model that is independent of any macroscale position vector. Nonconservative forces other than friction include other contact forces, tension, compression, and drag. However, for any sufficiently detailed description, all these forces are the results of conservative ones since each of these macroscopic forces are the net results of the gradients of microscopic potentials.
answer:
gradient of potentials


question:
What do you need in addition to the LaserDisc in order to experience surround sound?, Context: Only one 5.1 surround sound option exists on a given LaserDisc (either Dolby Digital or DTS), so if surround sound is desired, the disc must be matched to the capabilities of the playback equipment (LD Player and Receiver/Decoder) by the purchaser. A fully capable LaserDisc playback system includes a newer LaserDisc player that is capable of playing digital tracks, has a digital optical output for digital PCM and DTS audio, is aware of AC-3 audio tracks, and has an AC-3 coaxial output; an external or internal AC-3 RF demodulator and AC-3 decoder; and a DTS decoder. Many 1990s A/V receivers combine the AC-3 decoder and DTS decoder logic, but an integrated AC-3 demodulator is rare both in LaserDisc players and in later A/V receivers.
answer:
playback equipment


question:
Which of the following was on the same side as the UN: the U.S. or North Korea?, Context: Because neither Korea had a significant navy, the Korean War featured few naval battles. A skirmish between North Korea and the UN Command occurred on 2 July 1950; the U.S. Navy cruiser USS Juneau, the Royal Navy cruiser HMS Jamaica, and the frigate HMS Black Swan fought four North Korean torpedo boats and two mortar gunboats, and sank them. USS Juneau later sank several ammunition ships that had been present. The last sea battle of the Korean War occurred at Inchon, days before the Battle of Incheon; the ROK ship PC-703 sank a North Korean mine layer in the Battle of Haeju Island, near Inchon. Three other supply ships were sunk by PC-703 two days later in the Yellow Sea. Thereafter, vessels from the UN nations held undisputed control of the sea about Korea. The gun ships were used in shore bombardment, while the aircraft carriers provided air support to the ground forces.
answer:
the U.S