Electrostatic Forces. Atoms: protons (p+) bound in nucleus electrons (e-) freer to move about e- and p+ have equal amounts but opposite charge When objects rub together, electrons may be exchanged Objects that have more e- than p+ are negative
Example Problem: A penny has a charge of -1.00 x 10 -15 C. How many
More electrons than protons does it have?
Answer: #e- = q x e-/q
-1.00 x 10-15 C x 6.24 x 1018 e-/C = 6.24 x 10 3 excess e-
Conductors and insulators
Charging Objects: Friction
Charging Objects: Conduction
Charging Objects: Induction
Remember the general form for Gravitational force?
G = 6.67 x 10-11 Nm2/kg2
Well electrostatic force is another “force-at-a-distance”, and
Has a very similar form….
k = 8.99 x 109
k = 8.99 x 109 Nm2/C2
Use this equation to find the magnitude of the mutual force on any two point charges. Don’t bother plugging in the signs of the charges.
If the point charges have opposite signs, the force is attraction. If they have the same sign the force is repulsion.
Each object experiences the same amount of force, even if one has more charge or mass – remember Newton’s third law!
Lets compare the gravitational and electrostatic forces on a proton
and electron located 1.0 m apart….
me- = 9.11 x 10-31 kg qe- = -1.60 x 10-19 C
mp+ = 1.67 x 10-27 kg qp+ = +1.60 x 10-19 C
G = 6.67 x 10-11 Nm2/kg2 k = 8.99 x 109 Nm2/C2
Fg = 1.01 x 10-67 N
Fe = -2.30 x 10-28 N
Given q1, q2, and q3 and the distances between them, find the net force on q1 due to the other two