1. Foundations of Physics
Electrostatics

2. Four Fundamental Forces
Gravity
Cosmic and Macroscale
Electromagnetic
Macroscale and
Microscale
Weak
Strong
Subatomic
Nuclear

3. Electromagnetic Force
Force of attraction or repulsion due to an imbalance of electric charge
Opposite Charges Attract
Like Charges Repel

4. Electric Charge
Atoms are composed of positive protons, neutral neutrons, and negative electrons
Neutral atoms
have equal numbers of
positive protons and negative electrons

5. Electric Charge
Protons and neutrons are locked in the nucleus and can not move freely
Electrons are found outside the nucleus in energy levels and are free to move
A positive or negative electric charge results from objects gaining or losing electrons

6. Conservation of Charge
When electrons are transferred from one object to another, no electrons are created or destroyed.
The electrons removed from one object equals the electrons added to another object.

7. Charging By Friction Results from rubbing objects together
Called triboelectric charging
Friction strips electrons from atoms of one object and deposits them on another object
Friction transfers the electrons from the sweater to the balloon
The balloon and sweater have a balance of electric charge initially
Resulting in a slightly more positive sweater and a slightly more negative balloon

8. Electron Affinity
In some materials, the electromagnetic force of attraction between the positive nucleus and the negative electrons is very strong. This attraction is called electron affinity.
Electrons move from materials with low electron affinity to materials with high electron affinity.

9. Conductors and Insulators
Conductors are materials which allow electric charge to move through them easily.
Insulators are materials which do not allow electric charge to move through them easily.
Iron Nail
Plastic Rod
Electrons strongly bound to positive nucleus
Electrons are loosely bound to positive nucleus

10. Conduction Charging by contact
Charging a neutral object by making contact with a charged object
The resulting charge is always the same as the original charge.
Requires a conductor

11. Conduction
When a negatively charged object touches a neutral object, the repulsive force between the electrons pushes the mobile electrons off of the negative object and onto the neutral object.
Thus, the original negative charge is spread over both objects.
Objects are separated after initial touch
- Charged object touches neutral object
Both objects have a negative charge
Some electrons move onto sphere
Notice the negative charge on the original object is reduced because
some electrons moved to the sphere

12. Conduction
When a positively charged object touches a neutral object, the force of attraction pulls mobile electrons off of the neutral object onto the positively charged object
Results in both objects obtaining a positive charge
Objects are separated after initial touch
+ Charged object touches neutral object
Some electrons move to positive object
Both objects have a positive charge
Notice the positive charge on the original object is reduced because
some electrons moved onto the object from the sphere

13. Polarization
A negatively charged balloon is brought near a neutral sphere
The negatively charges repel the electrons of the sphere pushing them to the opposite side of the sphere.
Results in an object with two oppositely charged ends

14. Van de Graaff Generator
A motor at the base of the generator turns a large rubber belt which is stretched between two rollers located at each end of a long clear tube.
Metal Sphere
Rubber Belt
Motor in Base

15. Van de Graaff Generator
As the rubber belt moves over the rollers, electrons are removed from the rollers and begin to build up on the belt.
Wire brushes at the top of the clear tube remove the excess electrons from the belt and conduct the negative charge to the metal sphere at the top of the generator.

16. Van de Graaff Generator
The negative charge on metal sphere repels each other causing the charge to spread out evenly around the sphere.
When the electromagnetic force of repulsion becomes too large, the negative charge “jumps” off the sphere to another object or the air.

17. Induction
Charging of a neutral object by bringing a charged object near (but not touching) it.
Includes two processes: Polarization and Grounding
Results in two oppositely charged objects

18. Induction
The negative charged electrons on the sphere are removed by touching it with a finger (or other object)
Grounding – connecting a charged object to Earth to allow electrons to travel to or from the object depending on the situation

19. Induction
The finger (or grounding object) is removed and the balloon and sphere are separated
Notice the positive charge is
equal to the negative charge
on the original balloon (there
Is no reduction of charge)