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Removing electrons to make an object neutral is called grounding. Adding electrons to make an object neutral is also called grounding. The "ground" is able to supply or remove electrons to make an object neutral. In this situation you are connected to the "ground."

9. Negatively charge the rubber rod. Bring it close to the neutral Styrofoam ball, but do not touch the rod to the ball.

a) Describe your observations.
b) Like charges repel, and unlike charges attract. How would you explain the interaction between the charged rubber rod and the uncharged ball? (Hint: The electrons in the ball are able to move about the ball so that some are able to move closer to the rubber rod or further from the rubber rod.) Use a diagram to help you explain your observations.

Physics Words

Coulomb's Law: the relationship among electrical force, charges, and the distance between the charges.

FOR YOU TO READ
Coulomb's Law

In physics, scientists often search for an equation that can provide a clearer, more precise description of what they observe. Charles Augustin de Coulomb experimentally determined the equation for electric forces in 1784.

where F is the force in newtons (N),
q₁ and q₂ are charges in coulombs (C),
d is the distance between the centers of
the charges in meters (m), and
k is Coulomb's constant, always equal to
9 X 10⁹ Nm²/C².

Sample Problem
Two small charged spheres are placed
0.2 m apart. The first sphere has a charge of

+3.0 X 10^-6 C and the second sphere has a charge of - 4.0 3 10^-6 C. Calculate the force between them.

Strategy: You can use the equation for electric forces to calculate the force between the spheres.

Givens:
q1 = +3.0 X 10^-6 C
q2 = - 4.0 X 10^-6 C
d = 0.2 m

Solution:

F = -2.7 N
The negative sign indicates that the force is attractive.