In Mechanics: Check out this video, and take notes, as it will go through the details about rolling objects that have NO SLIPPING.
The NO SLIPPING is a key concept because it allows us to connect linear and rotational terms using s = R(theta), v = Rw, and a = R(alpha). If there is slipping, these are no longer valid relationships. ALSO, NO SLIPPING means there is NO ENERGY LOSS...there is friction, which creates the torque on the object, but it is effectively static friction. There is no heat generated by static friction.
In E&M: Check out this video, and take notes, regarding mass spectrometers. This will be the outline for applying F = qv x B, and a method for identifying specific atoms, particles, and molecules (that are ionized) by determining their masses. This is done by mv^2/R = qvB (remember that charges move in circles when in a magnetic field). By measuring the radius of curvature of the particles, and knowing the speed, charge and B-field, the mass can be calculated.
Note that a velocity selector is when both a B-field and E-field are used in the same region to make charge move in a straight line. Only particles with a specific speed can make it through when both the electric force, qE, is balancing the magnetic force, qvB. Set qE = qvB and you get a speed of v = E/B. We select the two fields, and therefore can select the speed of the particles that enter the magnetic field. For a simulation of a mass spectrometer, check out this ActivPhysics simulation.