During when does electrostatic force appear? Does moving a bent finger closely to a van degraff generator considered to exhibit electrostatic force?
Electrostatic force appears when there are electric charges present. It occurs between charged objects that are not in motion.
When you move a bent finger closely to a Van de Graaff generator, it does not exhibit electrostatic force itself, but rather experiences the effects of electrostatic force. The Van de Graaff generator generates static electricity, which creates an electric field around it. When you bring a charged object, such as a bent finger, near the generator, it can experience the attraction or repulsion due to the electrostatic force between the charges on your finger and the generator. So, the interaction between your bent finger and the Van de Graaff generator involves the effects of the electrostatic force, but the force itself is not generated by your finger.