When two objects attract each other electrically do both of them need to be charged?

Answer 1

There are a several examples where electrostatic attraction exists between two object when there may be no net charge on one or both.

The simplest case is polarization when a charged object brought near a neutral object. There will be an attraction which is larger of the neutral object is a conductor. The cause of the attraction is the induced polarization of the neutral object as a consequence of the electric field it experiences due to the charged object. The neutral object has an equal number of psotive and negative charges, but the positive charge are pretty much held in place by whatever chemical bonds are present. The electrons are freer to move and, especially in a conductor, will move towards or away from the charged object depending on whether it is potively or negatively charged. As a result, the redistribution of charge on the neutral object is such that the opposite to the original external charge are left closest to the original eternal charge and the remaining neutral object charge is further away and the same sign as he external object charge. Since the neutral object is now polarized with opposite and neutral charges are of the same magnitude, the attraction of the set of charges closest to the external charge is greater than the repulsion because the closer charges have the greater force.

There is one more example, but one does not see this easily because it is

between atoms. It allows atoms to attract each other even when they are neutral atoms. It is called the van der Waals force or the London dispersion force. It is a consequence of the dynamical motions of the electrons in the two neutral atoms. Basically, they slosh back and forth in a way that they form oscillating dipoles pointing alternately in opposite directions to produce a net attraction. To explain this in a proper scientific manner requires quantum mechanics, but the classical idea of coordinated dynamic dipoles is actually qualitatively the right idea.

Finally, it is true in general that two neutral objects may have dipoles or quadrupoles or more comlicated multiples and there will in all these cases be electrical forces between them. Those forces may be attractive or repulsive depending on the orientation of the object.

Answer 2

Yes,they should have same type of charge.