Question

¿Qué son las cargas positivas y negativas?

Answer 1

All the bodies that surround us are composed of electrons, protons and neutrons. In many cases the amount of protons and electrons is not the same (the body is not electrically balanced).
In the case that a body has more electrons than protons it is said to be negatively charged and if it has more protons than electrons it is said to be positively charged.
When the amount of protons and electrons is the same, the charge is zero or neutral (the body is not charged). In the following diagram two bodies with zero or neutral charge are presented.
For a body to be charged, either positively or negatively, it has to be affected in some way. One way to alter the body (assume a metal), is to heat it. In this case the body acquires more or less electrons, since the number of protons remains generally constant.
When electrons pass from one body to another, the body that loses electrons is positively charged and the one that gains electrons is negatively charged. This movement of electrons is what is called electric current.
The metals allow an easy flow of electrons. This flow may be due to the action of electrostatic forces. When this is the case, it is said that the electrons are under the effect of an electrostatic field, also called an electric field.