As the example implies, gravitational force is completely negligible on a small scale, where the interactions of individual charged particles are important. On a large scale, such as between the Earth and a person, the reverse is true. Most objects are nearly electrically neutral, and so attractive and repulsive
Coulomb forces nearly cancel. Gravitational force on a large scale dominates interactions between large objects because it is always attractive, while Coulomb forces tend to cancel.
Test prep for ap courses
For questions 25–27, suppose that the electrostatics force between two charges is
F .
What will be the force if the distance between them is halved?
Two massive, positively charged particles are initially held a fixed distance apart. When they are moved farther apart, the magnitude of their mutual gravitational force changes by a factor of
n . Which of the following indicates the factor by which the magnitude of their mutual electrostatic force changes?
Frenchman Charles Coulomb was the first to publish the mathematical equation that describes the electrostatic force between two objects.
Coulomb's law gives the magnitude of the force between point charges. It is
where
and
are two point charges separated by a distance
, and
This Coulomb force is extremely basic, since most charges are due to point-like particles. It is responsible for all electrostatic effects and underlies most macroscopic forces.
The Coulomb force is extraordinarily strong compared with the gravitational force, another basic force—but unlike gravitational force it can cancel, since it can be either attractive or repulsive.
The electrostatic force between two subatomic particles is far greater than the gravitational force between the same two particles.
Conceptual questions
[link] shows the charge distribution in a water molecule, which is called a polar molecule because it has an inherent separation of charge. Given water's polar character, explain what effect humidity has on removing excess charge from objects.
Schematic representation of the outer electron cloud of a neutral water molecule. The electrons spend more time near the oxygen than the hydrogens, giving a permanent charge separation as shown. Water is thus a
polar molecule . It is more easily affected by electrostatic forces than molecules with uniform charge distributions.
