1. Friction, Conduction, and Induction p279-281
9.2 Charging Objects
Friction, Conduction, and Induction p

2. Charging by Friction: Rubbing two objects together
Remember: Charging an object can only occur by the transfer of electrons from one object to another.
CHARGING BY FRICTION occurs when two objects are rubbed together
In this example, both hair and comb start neutral but after being rubbed together the comb is neg and hair positively charged.
When a charged object touches another object, electrons can be transferred between the objects. Electrons transfer from the object that has the more negative charge to the one that has the more positivecharge.

3. Balloon Demo

4. Example of Friction causing transfer of electrons between a balloon and sweater
Both items start relatively neutral
Latex has a higher affinity for electrons than the sweater
Rubbing allows electrons to be pulled off sweater to balloon,
Leaving both objects with an imbalance of charge:
Sweater “+”, balloon “-”
Rubber has a much greater attraction for electrons than animal fur/hair/sweater. As a result, the atoms of rubber pull electrons from the atoms of animal fur, leaving both objects with an imbalance of charge.

5. Attraction Between Charges Objects and Neutral Objects
Neutral objects have an equal number of protons and electrons.
Therefore, they have an equal number of positive and negative charges.
When you bring a charged object near a neutral object, the electron in the neutral object do not come off. Instead, the positive and negative charges in the molecules of the object stretch apart from each other.
Why charged balloon sticks to Neutral wall: the negative charges in the wall are pushed away from the surface by the negative charges on the balloon. Then the positive ends of the molecules in the wall are attracted to the negative charges of the balloon. These forces of attraction are strong enough to hold the balloon to the wall.

7. Electrostatic Series
A list of materials that are more likely to attract a negative charge when friction is applied to them. 
What type of charge does rubber acquire when rubbed with a nylon cloth?
What type of charge does the nylon cloth acquire?
How does the size of the charge on the rubber compare to the size of the charge on the cloth?

8. Electroscope
An electroscope detects static electricity by using thin metal or plastic leaves, which separate when charged.
An object with a suspected static electric charge is brought near the metal plate or ball of the electroscope.

9. Activity 9A p292
When two objects are rubbed together, what charge does each material acquire?
Complete the chart on page 292.
Follow instructions
Answer: Analysis Questions a-d and Evaluation e-g in COMPLETE SENTENCES.
You can make your own pith ball

10. Homework
Read Pages
CYU p281

11. Charging By Conduction (Contact)
Charging by Conduction occurs when objects touch and an electric charge is transferred from one object to the other.
Eg. Walk across a carpet and get a spark by touching a metal doorknob, yu are transferrig someof your charge to the doorbkow by conduction.

12. Charging by Induction
Occurs when objects are charged WITHOUT TOUCHING.
Eg. Build up of dust on TV or computer screen.
When screen is turned on, it begins to buld up a charge. When a neutral dust particle coes near the screen, the screen induces an opposite charge onteh near side of the dust particle and a similar charge on the far side. The dust is attracted tot the screem.

13. Activity 9B Electroscope np 294-295
Use an electroscope to investigate how different materials are charged by induction and conduction.
Follow instructions in you text.
Answer Questions a-j

14. Homework
Read pages
Answer CYU p 281 #

15. Insulators and Conductors
Material that do not let electrons move through them easily are called insulators. (glass, air, plastic, rubber, and wood.)
Material that do let electrons move through them easily are called conductors (copper, aluminum, gold, and silver).
Grounding.

16. Induced Separation of Charge
When negatively charged object is brought to neutral electroscope the electroscope becomes charged and the two leaves separate. (induced separation of charge) . Remove charged object and leaves will return to normal

17. Grounding
To ensure electroscope is neutral, it needs to have all the excess charges removed, or discharged.
This is done by grounding the object.
A grounded object is connected directly to Earth by a conductor .
An electroscope containing conducting metal but holds a static charge. Why?
An electroscope containing conducting metal but holds a static charge because it is not in direct contat with its surroundinsg.

18. Isolating Charges: Faraday Cage
A Faraday Cage is a grounded metal screen surrounding a piece of equipment to exclude electrostatic influences.
Car is the safest place in a lightning storm. Cell phones don’t work well in elevators. Car radio in tunnels.

19. Attracting Charges: Lightning Rod
Pointed to receive a greater concentration of charge.
Received concentrated positive charge if a negatively charge cloud is above the building.

20. Electrostatic Force
Electrostatic Force is the attraction or repulsion of objects due to their electric charge
A force is a push or pull acting on an object, measured in newtons (N)
If force is unbalanced, it can cause an object to move.
An electrostatic force is the force that exists between static charges.
It can either pull the static charges together (force of attraction) or push static charges apart (force of repulsion).
Roll pop can

21. Electric Force Depends on:
Type of charge on the objects (positive, negative, neutral)
Amount of charge on the objects
Distance between objects
The stronger the charge on objects, the stronger the electric force.
As distance increases, electric force decreases.

22. Van de Graaff
Allows you to see how like charges repel and opposite charge attract
Use to investigate factors that affect the strength of the electric force.

23. Van de Graaff generator
Generates very high electric charge.
Motor turns rubber belt
Charge comb picks up negative charges from belt
Belt transfers charge to dome
An electrostatic generator
Used to research static electricity and to make static charges available for experimentation

24. Van de Graaf Generator, Activity p286
Safety
Always stand on insulated surface
Discharge dome often with grounding rod
Wait for dome to be grounded and belt to be turned off before taking hands off
Answer questions p #1,2,7,9

25. Van de Graaf Generator What is it? How does it work?
Produces very large electric charges
Electric force is force that exists between static charges (can either attract or repel objects)
How does it work?
Motor turn rubber belt
Charge comb picks up negative charges from belt
Transfer charge to dome

26. Van de Graaff
As the charge builds up on the dome, the electric force between the dome and the discharge ball increases.
DIRECT RELATIONSHIP: as the electric force increase as the charge increases.
However, as distance decreases, the electric force increases (INVERSE RELATIONSHIP)

27. Coulomb’s Law
Charles Coulomb recognized the relationships between electric force, size of charge and distance
Coulomb’s Law: the strength of the electric force increases with increasing electric charges and decreases with increasing distance.
Size of electric charge measured in coulombs (C)

28. Homework
Read pages
Answer CYU p287 #1, 2, 3, 5, 9,

29. Check Your Understanding
During a physics lab, a plastic strip was rubbed with cotton and became positively charged. The correct explanation for why the plastic strip becomes positively charged is that ...
a. the plastic strip acquired extra protons from the cotton.
b. the plastic strip acquired extra protons during the charging process.
c. protons were created as the result of the charging process.
d. the plastic strip lost electrons to the cotton during the charging process.

30. CYU #2
Saran Wrap has a larger electron affinity than Nylon. If Nylon is rubbed against Saran Wrap, which would end up with the excess negative charge? ____________ Explain.

31. CYU #3
A physics teacher rubs a glass object and a felt cloth together and the glass becomes positively charged. Which of the following statements are true? Circle all that apply.
a. The glass gained protons during the rubbing process.
b. The felt became charged negatively during this rubbing process.
c. Charge is created during the rubbing process; it is grabbed by the more charge-hungry object.
d. If the glass acquired a charge of +5 units, then the felt acquires a charge of -5 units.
e. This event violates the law of conservation of charge.
f. Electrons are transferred from glass to felt; protons are transferred from felt to glass.
g. Once charged in this manner, the glass object and the felt cloth should attract each other.
h. In general, glass materials must have a greater affinity for electrons than felt materials.

32. CYU #4
Which statement best explains why a rubber rod becomes negatively charged when rubbed with fur?
a. The rubber that the rod is made of is a better insulator than fur.
b. The fur is a better insulator than the rubber.
c. Molecules in the rubber rod have a stronger attraction for electrons than the molecules in the fur.
d. Molecules in the fur have a stronger attraction for electrons than the molecules in the rubber rod.

33. What’s happening here?

34. Example
You transfer some of your charge to the metal door knob.

35. Charging by Conduction - Examples
an uncharged physics student stands on an insulating platform and touches a negatively charged Van de Graaff generator.
he neutral physics student becomes charged as the result of contact with the Van de Graaff generator.

36. Charging by Induction
Charging by Induction occurs when objects are charged without actually touching

37. Charging by Induction
Example: build up of dust on the computer screen:
When a computer is turned on, it begins to build up a charge
When a neutral dust particle come near the scree, the screen induces a opposite charge on the near side of the dust particle and a similar charge on the far side.
The dust is attracted to the screen

38. Charging by Induction
Object is charged without actually touching any other charged object
Bring a negatively charged rod near – but not touching- the sphere , the rod will repel the electrons in the sphere. The negative charges will move down the leaves and the leaves will repel each other.
The sphere is left with a temporary positive charge
If the negative rod is removed, the electrons will move back to the sphere and the sphere will become neutral again.
Example: dust build up on TV or computer screen

39. Electroscope
instrument that detects the presence of charge of an object.
Needs to be grounded (by touching with fingers) between tests.
It was the first electrical measuring instrument.
Electrical charges move to the metal and down to the foil leaves, which then repel each other. Since each leaf has the same charge (positive or negative), they repel each other.
Charging Electroscope by Induction: Touch the electroscope and bring a charged rod close. If the charged rod is negative, electrons from the electroscope will flow onto your body. Now remove your hand and then move the charged rod away. The electroscope will be left with a deficit of electrons giving it a positive charge.

40. Why are neutral objects attracted to charged objects?
because the neutral objects are temporarily charged by induction.
A negatively charged balloon sticks to a neutral wall because the balloon’s negative charges repel the wall’s negative charges.
A positive charge is induced on the surface of the wall
the negative balloon is attracted to the positive wall surface.

41. Check Your Understanding
Two neutral conducting pop cans are touching each other. A positively charged balloon is brought near one of the cans as shown below. The cans are separated while the balloon is nearby, as shown. After the balloon is removed the cans are brought back together. When touching again, can X is ____.
a. positively charged
b. negatively charged
c. neutral
d. impossible to tell

42. CYU #2
Two neutral conducting pop cans are touching each other. A positively charged glass rod is brought near Can X as shown below. Which of the following occur as the glass rod approaches Can X? List all that apply.
a. Electrons jump from the glass rod to can X.
b. Electrons jump from the glass rod to can Y.
c. Electrons jump from can X to the glass rod.
d. Electrons jump from can Y to the glass rod.
e. Protons jump from the glass rod to can X.
f. Protons jump from can X to the glass rod.
g. ... nonsense! None of these occur.

43. CYU #3
TRUE or FALSE?
Two neutral conducting pop cans are touching each other. A negatively charged balloon is brought near Can X as shown below. As the balloon approaches Can X, there is a movement of electrons between the balloon and can X (in one direction or the other).
a. TRUE b. FALSE

44. CYU #4
A positively charged balloon is brought near a neutral conducting sphere as shown below. While the balloon is near, the sphere is touched (grounded).
At this point, there is a movement of electrons. Electrons move ____ .
a. into the sphere from the ground (hand)
b. out of the sphere into the ground (hand)
c. into the sphere from the balloon
d. out of the sphere into the balloon
e. from the ground through the sphere to the balloon
f. from the balloon through the sphere to the ground
g nonsense! Electrons do not move at all.

45. CYU #5
Suppose that a negatively charged balloon is used to charge an electroscope by induction. The procedural steps are described in the educational cartoon below. On the cartoon, draw the orientation of the needle and indicate the location and type of any excess charge in steps ii. - v. Explain in terms of electron movement what is happening in each step.

46. Answer #5

47. CYU #6
A negatively charged balloon is brought near a neutral conducting sphere as shown below. As it approaches, charge within the sphere will distribute itself in a very specific manner. Which one of the diagrams below properly depicts the distribution of charge in the sphere?

48. CYU #7
A positively charged piece of Styrofoam is placed on the table. A neutral aluminum pie plate is brought near as shown below. While held above the Styrofoam, the aluminum plate is touched (grounded).
At this point, there is a movement of electrons. Electrons move ____ .
a. out of the aluminum plate into the ground (hand)
b. into the aluminum plate from the ground (hand)
c. into the aluminum plate from the Styrofoam
d. out of the aluminum plate into the Styrofoam
e. from the ground through the aluminum plate to the Styrofoam
f. from the Styrofoam through the aluminum plate to the ground
g nonsense! Electrons do not move at all.

49. CYU #2
Which of the diagrams below best represents the charge distribution on a metal sphere when a positively charged plastic tube is placed nearby?

50. CYU #5
Charged rubber rods are placed near a neutral conducting sphere, causing a redistribution of charge on the spheres. Which of the diagrams below depict the proper distribution of charge on the spheres? List all that apply.