When there is a changing magnetic field, electric fields are produced. If this changing magnetic field, and hence resulting electric field, occurs in a metal, currents will result. These currents are called eddy currents. Eddy currents generated in a pendulum are shown to abruptly stop a pendulum, an example of magnetic braking. When there are grooves in the pendulum, thus reducing the amount of eddy currents that can flow, little braking is observed.