What are Eddy Currents?

Eddy currents are currents induced in conductors when exposed to a changing magnetic field due to relative motion of the field source and conductor; or due to variations of the field with time. This can cause a circulating flow of electrons within the body of the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsive, attractive,propulsion and drag effects. The stronger the applied magnetic field, or the greater the electrical conductivity of the conductor, or the faster the field changes, then greater the currents that are developed and the greater the fields produced.
 
Eddy currents, like all electric currents, generate heat as well as electromagnetic forces. The heat can 
be harnessed for induction heating. The electromagnetic forces can be used for levitation, creating movement, or to give a strong braking effect. 

Eddy currents can also have undesirable effects, for instance power loss in transformers.

What is short circuit?

A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit. This results in excessive current flow in the power source through the 'short,' and may even cause the power source to be destroyed. If a fuse is in the supply circuit, it will do its job and blow out, opening the circuit and stopping the current flow.

Short circuits can produce very high temperatures due to the high power dissipation in the circuit.