This HTML 5 app shows a direct current electrical motor which is reduced to the most important parts for clarity. Instead of an armature with many windings and iron nucleus there is only a single rectangular conductor loop; the axis the loop rotates on is omitted.
The red arrows indicate the conventional direction of current (from plus to minus). You can recognize the magnetic field lines (directed from the red painted north pole to the green painted south pole) by the blue color. The black arrows represent the Lorentz force which is exerted on a current-carrying conductor in the magnetic field.
The mentioned Lorentz force is perpendicular to the direction of current and to the magnetic field lines. The orientation of this force results from the well-known three finger rule (for the right hand!):
|Thumb:||Conventional direction of current|
|Middle finger:||Lorentz force|