In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

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.
gradient of potentials

The Russian Civil War included what non-Russians?, Context: The principal fighting occurred between the Bolshevik Red Army and the forces of the White Army. Many foreign armies warred against the Red Army, notably the Allied Forces, yet many volunteer foreigners fought in both sides of the Russian Civil War. Other nationalist and regional political groups also participated in the war, including the Ukrainian nationalist Green Army, the Ukrainian anarchist Black Army and Black Guards, and warlords such as Ungern von Sternberg. The most intense fighting took place from 1918 to 1920. Major military operations ended on 25 October 1922 when the Red Army occupied Vladivostok, previously held by the Provisional Priamur Government. The last enclave of the White Forces was the Ayano-Maysky District on the Pacific coast. The majority of the fighting ended in 1920 with the defeat of General Pyotr Wrangel in the Crimea, but a notable resistance in certain areas continued until 1923 (e.g., Kronstadt Uprising, Tambov Rebellion, Basmachi Revolt, and the final resistance of the White movement in the Far East).
volunteer foreigners

Why would a party notify the other party?, Context: Treaties are not necessarily permanently binding upon the signatory parties. As obligations in international law are traditionally viewed as arising only from the consent of states, many treaties expressly allow a state to withdraw as long as it follows certain procedures of notification. For example, the Single Convention on Narcotic Drugs provides that the treaty will terminate if, as a result of denunciations, the number of parties falls below 40. Many treaties expressly forbid withdrawal. Article 56 of the Vienna Convention on the Law of Treaties provides that where a treaty is silent over whether or not it can be denounced there is a rebuttable presumption that it cannot be unilaterally denounced unless:

to withdraw