Muggles' Guide to Harry Potter/Magic/Locomotor

Overview
Used in the form "Locomotor object", e.g. "Locomotor trunk", this causes the named object to lift up and move as though the wizard casting the spell were carrying it.

Extended Description
This spell is used numerous times in the books; it is used whenever a wizard needs to carry a large load at about a walking pace. When the spell is cast on an object (usually a trunk), the object lifts, and follows the spell-caster.

Analysis
The Locomotor spell seems to be speed limited: in Harry Potter and the Order of the Phoenix, Tonks uses this spell to bring Harry's trunk downstairs to where the rest of the Advance Guard are waiting; but it is then strapped to a broom for the high-speed journey to London, which probably means that the Locomotor spell is not strong enough to keep the trunk with Tonks at speed. It is apparently capable of lifting things up stairs, as Professor Flitwick uses this spell to help him carry Sybill Trelawney's trunks back up to her tower room, after Professor Umbridge sacks her in Harry Potter and the Order of the Phoenix.

Greater Picture
Curiously, despite the apparent similarity to the spell Locomotor Mortis, first seen in Harry Potter and the Philosopher's Stone, the latter is the Leg-Locker jinx, meaning that the "locomotor" in that case must refer to the victim's legs. Clearly there must be some mental component that changes the effect from that of causing a body to move, as we would expect from a casual inspection of the jinx. We also note that the equivalent for moving a body, as seen in Harry Potter and the Prisoner of Azkaban, is Mobilicorpus.