A rotor for an electric motor, the rotor configured to rotate about a longitudinal axis in use, the rotor comprising: one or more permanent magnets or windings; and a layer of material disposed over the permanent magnets or windings; wherein the rotor has a length (L 1) between a first longitudinal end and a second longitudinal end, characterised in that: the layer of material comprises one or more grooves or channels for, opening into the gap forming a mechanical clearance between the rotor and a stator of the electric motor, directing fluid along the rotor, each groove or channel of the one or more grooves or channels comprising: a leading portion that begins at the first longitudinal end of the rotor and extends towards the second longitudinal end of the rotor, wherein a path formed by the leading portion has a direction having a component in a longitudinal direction of the rotor and a component in a circumferential direction of the rotor; a longitudinally central portion which is fluidly connected to the leading portion, wherein a path formed by the central portion is substantially parallel to the longitudinal axis; and a trailing portion which is fluidly connected to the central portion at an opposite longitudinal side thereof to the leading portion, and which extends towards the second longitudinal end of the rotor, wherein a path formed by the trailing portion has a direction having a component in the longitudinal direction of the rotor and a component in the circumferential direction of the rotor, wherein the leading portion extends around the rotor in a first circumferential direction as a function of distance from the first longitudinal end of the rotor towards the central portion, and the trailing portion extends around the rotor in the first circumferential direction as a function of distance from the central portion to the second longitudinal end of the rotor, such that the one or more grooves or channels are substantially S-shaped. one or more permanent magnets or windings; and a layer of material disposed over the permanent magnets or windings; wherein the rotor has a length (L 1) between a first longitudinal end and a second longitudinal end, characterised in that: the layer of material comprises one or more grooves or channels for, opening into the gap forming a mechanical clearance between the rotor and a stator of the electric motor, directing fluid along the rotor, each groove or channel of the one or more grooves or channels comprising: a leading portion that begins at the first longitudinal end of the rotor and extends towards the second longitudinal end of the rotor, wherein a path formed by the leading portion has a direction having a component in a longitudinal direction of the rotor and a component in a circumferential direction of the rotor; a longitudinally central portion which is fluidly connected to the leading portion, wherein a path formed by the central portion is substantially parallel to the longitudinal axis; and a trailing portion which is fluidly connected to the central portion at an opposite longitudinal side thereof to the leading portion, and which extends towards the second longitudinal end of the rotor, wherein a path formed by the trailing portion has a direction having a component in the longitudinal direction of the rotor and a component in the circumferential direction of the rotor, wherein the leading portion extends around the rotor in a first circumferential direction as a function of distance from the first longitudinal end of the rotor towards the central portion, and the trailing portion extends around the rotor in the first circumferential direction as a function of distance from the central portion to the second longitudinal end of the rotor, such that the one or more grooves or channels are substantially S-shaped. a leading portion that begins at the first longitudinal end of the rotor and extends towards the second longitudinal end of the rotor, wherein a path formed by the leading portion has a direction having a component in a longitudinal direction of the rotor and a component in a circumferential direction of the rotor; a longitudinally central portion which is fluidly connected to the leading portion, wherein a path formed by the central portion is substantially parallel to the longitudinal axis; and a trailing portion which is fluidly connected to the central portion at an opposite longitudinal side thereof to the leading portion, and which extends towards the second longitudinal end of the rotor, wherein a path formed by the trailing portion has a direction having a component in the longitudinal direction of the rotor and a component in the circumferential direction of the rotor, wherein the leading portion extends around the rotor in a first circumferential direction as a function of distance from the first longitudinal end of the rotor towards the central portion, and the trailing portion extends around the rotor in the first circumferential direction as a function of distance from the central portion to the second longitudinal end of the rotor, such that the one or more grooves or channels are substantially S-shaped.