- Normal Phase Change: Events involving phase change at one atmosphere.

Consider the position of a BODY that moves in 0XYZ - space. At a time (no time specifically but a time, **t = t***) an implicit mathematical statement of that position is **P(t*)** (below left).

(1)This the implicit position of a BODY at a time, |
(2)This the new (implicitly stated) position of the same BODY a short time later (at the time, |

Our interest is motion of the BODY until a time later, the inspecific time, **t = t* + Δt** where the notation **Δt** is called "an increment in time." By symbol, the position of the BODY at the later time is written (above right).