1. Four Fundamental Forces
Gravity
Attractive only
Property of Mass
Light responds to gravity
Can be thought of as a reshaping of space-time
Electro-Magnetism
Interaction of charged particles
Responsible for ALL surface interactions of matter
Responsible for molecular bonding
Strong Nuclear Force
Holds the Protons and Neutrons together in the nucleus of the atom
Weak Nuclear Force
Responsible for nuclear radiation & fission

2. What Is Static Electricity?
When extra electrons or protons build up on an object it becomes “charged”.

3. What Is Static Electricity?
Static means “not moving”
Electric Charges move from one object to another, but then remain there.
Charge is not continuously moving.

4. Balloon Demo
Questions you should be able to answer by the end of class?
Why does the balloon stick to the wall?
Why do you have to rub the balloon first for it to work?
Why does the balloon eventually fall?
How is the balloon sticking similar to a magnetic attraction?

5. Where do charges come from?
All charges come from atoms.
All we can ever do is transfer electrons from one object to another.
Charge is a CONSERVED quantity. We CAN NOT make (or destroy) charge!**
**When an electron is created in a particle accelerator, and anti- electron also forms, so that the net charge remains = 0. –

6. Where do charges come from?
All charges come from atoms. + –
Proton (positive charge) +
neutron (neutral)
electron (negative charge) –
atom
nucleus
Protons are fixed in the nucleus  Electrons are free to move

7. Electrical Charge, q Charge of an electron: qe = 1.60 x 10-19 C
Unit: Coulomb (C)
Charge of an Proton: +1.6 x C
1 Coulomb = 6.25x1018 protons
 1 Coulomb = 6.25x1018 electrons

8. Practice Problem
A metal ball has a charge of −20 nC. How many excess electrons are there? −20× 10 −9 C electrons −1.60× 10 −19 C =125× 10 9 electrons

9. How do you get Charge off an Atom?
You rub it off
When rubbed together, all objects become charged to some extent
Ancient Greeks noticed that you could generate electricity by rubbing amber with fur
ελεκτρον – “electron” means amber
PhET Sweater-Balloon Simulation

10. Charging (without a credit card)
Charging by friction: Some objects are electron attractors, others are electron donators.
Insulators are easily charged by friction, because charges cannot move easily once on them.
Conductors do not charge easily by friction because extra charges gained move easily off of them.
Chemical Processes Also Separate Charge (create ions)

11. Triboelectric series (electron affinity)
More Positive
DRY Human Hands
Leather
Rabbit Fur
Glass
Human Hair
Nylon
Wool
Fur
Lead
Silk
Aluminum
Paper
Cotton
Steel (neutral)
Wood
Amber
Hard Rubber
Nickel, Copper
Brass, Silver
Gold, Platinum
Polyester
Styrene (Styrofoam)
Saran Wrap
Polyurethane
Polyethylene (scotch tape)
Polypropylene Vinyl (PVC)
Silicon
Teflon 
More Negative

12. Three Charge States neutral # electron = # protons Positive
# electrons < # protons (electrons lost)
# electrons > # protons (electrons gained)
negative

13. Quick Quiz: What is the charge on most objects?
Most objects are neutral.
How do we know this?
When we touch them they don’t shock us!

14. What Holds the Balloon to the Wall? and stops if from falling?
There must be a FORCE
Coulomb’s Force!

15. Electric Force: Coulomb’s Law
Originally derived by 18th Century French physicist Charles Coulomb
Describes interaction force for electrically charged objects
Experimentally verified in modern times
No exceptions found so far (even at distances within the atom)

16. Electric Force: Coulomb’s Law
UNITS: Newtons (N)
q = first point charge in Coulombs (C)
Q = second point charge in Coulombs (C)
r = distance between q & Q
k = constant 8.988x109 or 8.99x109
From Textbook: Modern experiments have verified Coulomb’s law to great precision. For example, it has been shown that the force is inversely proportional to distance between two objects squared F ∝ 1 / r2 to an accuracy of 1 part in No exceptions have ever been found, even at the small distances within the atom.

17. Polarization Separation of charges in a neutral object.
Net charge of object remains zero!

18. Example 18.1
Calculate the force between an electron (e-) and a proton (p+) a distance of 0.530x10-10 m apart (average separation in a hydrogen atom)
What is the force at twice that distance
How does that compare to the Gravitational force between an electron and a proton?

19. Example 18.1
Calculate the force between an electron (e-) and a proton (p+) a distance of 0.530x10-10 m apart (average separation in a hydrogen atom)
F = x108 N (note: negative force is attractive)
What is the force at twice that distance
How does that compare to the Gravitational force between an electron and a proton?

20. Example 18.1
Calculate the force between an electron (e-) and a proton (p+) a distance of 0.530x10-10 m apart (average separation in a hydrogen atom)
F = x10-8 N (note: negative force is attractive)
What is the force at twice that distance
F = x10-8 N [note: ¼ of the force in (a)]
How does that compare to the Gravitational force between an electron and a proton?

21. Example 18.1
Calculate the force between an electron (e-) and a proton (p+) a distance of 0.530x10-10 m apart (average separation in a hydrogen atom)
F = x10-8 N (note: negative force is attractive)
What is the force at twice that distance
F = x10-8 N [note: ¼ of the force in (a)]
How does that compare to the Gravitational force between an electron and a proton?
FG = 3.61 x10-47 N gravitational force is times smaller than the electrical force between them

22. Two Types of Materials Charge can build up on both insulators
Insulators - Charges can not move easily.
most plastics
wood & paper
rubber
ceramics
PURE water
Conductors - charges CAN move freely.
metals – Copper (Cu), Aluminum (Al), Silver (Ag), Gold (Au), …
leather (somewhat)
Water containing salts or minerals
Charge can build up on both insulators
Not Easily Removed on an Insulator
Charge on Conductor moves to distribute evenly

23. Are YOU an insulator or a conductor?
Conductor … why?
You are about 80% salty water.
Electrons are mostly free to move on your sweaty skin (and into your wet, salty body).

24. The parts of a power cord.
Conductor on the inside (throughout which electrons can flow easily)
Insulator on the outside (to keep us from getting shocked)
non-conductive fibers strengthens the cord

25. Electrostatic Repulsion & Attraction
2 Types of Charge: (+) and ()
Like Charges Repel
Opposite Charges Attract + - + - + -

26. Fleft=8.99x10-4N to right and Fright=8.99x10-4N to left
Practice Problem1:
Two +10 nC charged particles are 2.0 cm apart on the x-axis. What is the net force on a +1.0 nC charge midway between them?
2.0 cm
+10 nC
+10 nC
+1 nC
Fleft=8.99x10-4N to right and Fright=8.99x10-4N to left
so, then Fnet = +8.99x10-4 N – 8.99x10-4 N = 0 N
Fnet = 0 N

27. Practice Problem 1:
Two +10 nC charged particles are 2.0 cm apart on the x-axis. What is the net force on a +1.0 nC charge midway between them?
What is the net force and E-field if the charged particle on the right is replaced by a −10 nC charge?
2.0 cm
Fleft=8.99x10-4N to right
+10 nC
-10 nC
+1 nC
Fright=8.99x10-4N to right
so, Fnet = +8.99x10-4 N x10-4 N = 18.0 x10-4 N
Fnet = 18.0 x10-4 N to the right

28. Electric Force & Electric Field
The force on the test charge according to Coulomb’s Law for a charge Q and test charge q
Electric Field, E (units N/C) E-field at a distance, r , away from charge Q.

29. What is the E-field for Practice Problem1:
Two +10 nC charged particles are 2.0 cm apart on the x-axis. What is the net force on a +1.0 nC charge midway between them?
What is the E-field at this point?
2.0 cm
+10 nC
+10 nC
Fnet = 0 N
+1 nC
Enet=Fnet/q where q is the 1 nC charge. Enet=0 N/C

30. What is the E-field for Practice Problem1B?
Two +10 nC charged particles are 2.0 cm apart on the x-axis. What is the net force on a +1.0 nC charge midway between them?
What is the E-field if the charged particle on the right is replaced by a −10 nC charge?
2.0 cm
Fnet = 18.0 x10-4 N
to the right
+10 nC
-10 nC
+1 nC
Enet=Fnet/q where q is the 1 nC charge.
Enet=(18.0x10-4 N)/(1x10-9C) = 1.80x106 N/C

31. Every Charge Generates an Electric Field
A positive test charge, q, will move in the direction of the field arrows.
A NEGATIVE charge, -q, will move OPPOSITE the direction of the field arrows
Charges move because the electric field induces a FORCE to accelerate them. + +q -q -

32. Electric Forces & Electric Fields
Electric force, F, & electric field, E, are vectors
E points in same direction as F
Vectors in the same direction add =
Vectors in opposite direction subtract =
Vectors at angles add according to
F1sin1
F1cos1 2
F2sin2
F1cos2
Fnet = F1cos1 +F2cos2 x-dir + F1sin1 +F2sin2 y-dir 1

33. mini quiz
A small, positive charge is placed at the black dot. In which case is the force on the small, positive charge the largest? A B C D

34. mini quiz
All charges in the diagrams are equal magnitude. In each case, a small positive charge is placed at the black dot. In which cases is the force on this charge:
to the right?
to the left?
zero?

35. Sample Problem- Three point charges of magnitude +1 C, +1 C and −1 C respectively are placed on the three corners of an equilateral triangle as shown. -
Which vector best represents the direction of the net force acting on the −1 C charge as a result of the forces exerted by the other two charges?
Fnet + + a) b) c) d)

36. How can we make a neutral object gain a positive or negative charge
How can we make a neutral object gain a positive or negative charge? 3 ways
Conduction – direct Contact with a positive or negatively charged object
Friction or Rubbing
Induction - the processing of charging a neutral conductor without contact by using a charged object and a path to ground or another neutral object