interaction magnetic.torque#

Describes the entry magnetic.torque at version 0.1.0, registered by mime.interactions.magnetic.MagneticTorque.

At a glance#

What it models, and when not to use it#

The torque of a field on a magnet#

What it models. The torque of the field bound to field on the body’s permanent magnetic moment, about the centre of mass: exp.attach(Magnetic.Torque(), body=umr, field=rpm.magnetic). The moment is the body’s magnetic_moment, in the body’s frame, turned into the world by the body’s orientation; the torque is its cross product with the flux density. It delivers no force: the pull of a field’s gradient on the moment is another law, Magnetic.Force, and the two are attached together for the whole of a magnet’s response. A field that varies in space is read at the body’s centre of mass, and a uniform field is read as it always was, with no points.

It reads the body’s pose at the start of the step, as every law reads its body’s state, so the torque of a step turns the body as it stood after the step before: a lag of one step in phase at a rotating field’s rate. Its reaction, the opposite torque on the field’s source, is delivered to the frame that source is mounted on wherever that frame’s segment takes loads: a segment on its dynamic rung. With Magnetic.Force’s reaction beside it, that is the whole of what the body’s moment exerts on a point dipole source. A source fixed in the world, or carried by a kinematic segment, takes none.

It is a member of the magnetic family: its sign, frame, units, closed form and gradients are checked by the family’s suite, and its reaction against the force and torque of the body’s dipole on the source’s. It is a complementary delivery to Magnetic.Force, not an alternative to it.

When not to use it.

  • Where the field varies across the body: it is read at one point, the body’s centre of mass.

  • Inside a point dipole source’s near field, where the source’s own model fails before this law does (see MIME-ANO-100).

  • When the reaction on a source carried by a kinematic segment matters: a prescribed motion takes no load, so the reaction is delivered only where the source’s segment is on its dynamic rung (see MIME-ANO-103).

  • For an induced moment, which depends on the field: the moment here is permanent.

  • When the lag of one step matters: it is a phase lag of the field’s rate times the timestep, so it grows with both.

Where its values come from. A declaration, a record or the body’s parts, and what “declared” means: the materials note.

Versions. magnetic.torque 0.1.0 is its first; it delivers its reaction on a source mounted on a segment that takes loads, which no earlier experiment had, so what it computes elsewhere is unchanged.

Settings#

none: the entry takes no setting, so its setting_roles declares none.

Roles, reads and deliveries#

Roles, bound by keyword when the entry is attached: body (body), field (field).

Reads:

Label

Reads

flux_density

field field.magnetic.flux_density

pose

body body.pose

Delivers:

Label

Role

Into the target

wrench

body

body.applied_wrench

Reads values of the things it is bound to:

Label

Role

Value

moment

body

magnetic_moment

Reads, values and deliveries that its plan adds for a particular construction are not in these tables: they list what the class declares, and plan is code the build runs when the entry is attached.

Nodes it builds#

Declared in builds; the node walk compares it with what a round-trip case builds.

Supported constructions, by what each bound thing’s dynamics or field provider must offer:

Requires

Note

body: flag rigid, accepts body.applied_wrench, publishes body.pose; field: flag uniform, publishes field.magnetic.flux_density

a permanent moment in a uniform field

body: flag rigid, accepts body.applied_wrench, publishes body.pose; field: flag provision=evaluated, publishes field.magnetic.flux_density

a permanent moment in a field that varies in space, read at the body’s centre of mass: valid while the field varies little across the body, and outside a point dipole’s near field (MIME-ANO-100)

Gradient status#

The derivative through this entry is exact, the derivative of what it computes.

Validity#

Declared validity lines: free text, not parsed, and not yet checked against the operating point or the region each one describes.

  • a permanent moment in a field that varies in space, read at the body’s centre of mass: valid while the field varies little across the body, and outside a point dipole’s near field (MIME-ANO-100)

Family#

Declared: magnetic. The family’s conformance suite is run by a test of the lab or of MIME; which test, and in which lane, is resolved when the evidence resolver lands.

References#

[@Ling2016UniversityPhysics2]

Other declarations#

Class variable

Type

Value

holds_off

ClassVar[str | None]

null

id_roles

ClassVar[tuple[str, ...] | None]

null

moving

ClassVar[bool]

false