Objects can become electrically charged through a process known as charging. This can happen in several ways, primarily through friction, conduction, and induction.
Friction: This is perhaps the most common method. When two different materials are rubbed together, electrons can be transferred from one material to the other. For example, if you rub a balloon against your hair, electrons from your hair are transferred to the balloon. This gives the balloon a negative charge, while your hair becomes positively charged. The charged balloon can now attract small pieces of paper or other lightweight materials.
Conduction: This method involves direct contact between a charged object and a neutral object. If a charged object touches a neutral one, the charge can spread to the neutral object. For instance, if a negatively charged rod touches a neutral metal sphere, electrons will transfer to the sphere, giving it a negative charge as well. The two objects will then have the same charge, and this can happen until the charges balance out.
Induction: This process does not require direct contact. When a charged object is brought near a neutral object, it can cause the electrons in the neutral object to rearrange. For instance, if a negatively charged rod is brought close to a neutral metal sphere, the negative charge in the sphere will move away from the rod, causing the near side of the sphere to become positively charged. If the rod is then removed, the sphere remains neutral unless it is grounded to allow the charges to balance out.
In summary, objects become electrically charged through the transfer or rearrangement of electrons, primarily via friction, conduction, or induction, leading to the creation of positive and negative charges.