1/31 do now

1. 1/31 do now • An object is thrown straight upward from Earth’s surface. Graph the following for the time that elapses while it is in the air: [Neglect friction.] • a-t • v-t • d-t

2. Due today • castle learning corrections • Review packets • Homework • 17.1 notes due Monday 2/3 • Castle learning : graphs • objectives • Go over midterm • Go over chapter 7 essays • Go over chapter 7 project • Lab – determine power

3. 2/4 do now • A cart travels with a constant nonzero acceleration along a straight line. Graph the following relationships: • Acceleration vs. time • Velocity vs. time • Distance vs. time

4. Objectives • Understand the basic properties of electric charge. • Differentiate between conductors and insulators. • Distinguish between charging by contact and charging by polarization. Homework: Castle learning: you have two days to do. If you did not finish in time, you can come post session to make up homework.

5. Atomic Structure Review Matter is made up of small structures called ATOMS Within the NUCLEUS are two types of NUCLEONS At the center of each atom is a NUCLEUS Orbiting the NUCLEUS are ELECTRONS ELECTRONS NEGATIVE charge Orbit nucleus PROTONS NEUTRONS POSITIVE CHARGE DO NOT MOVE WITHIN MATTER NO CHARGE – NEUTRAL DO NOT MOVE WITHIN MATTER

6. Charged Objects Objects are normally electrically NEUTRAL. They have the same number of protons and electrons If an object loses electrons, it becomes POSITIVELY charged If an object gains electrons, it becomes NEGATIVELY charged + - LACK OF ELECTRONS EXCESS ELECTRONS Only electrons can move, protons and neutrons can not move.

7. Example • Which part of an atom is most likely to be transferred as a body acquires a static electric charge? • proton • neutron • electron • positron

8. 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 ... the plastic strip acquired extra protons from the cotton. 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. Example

9. Charge Interactions The electric force is a non-contact force. Any charged object can exert this force upon other objects - both charged and uncharged objects. The nature of the electric force: Opposites attract. likes repel.

10. The Electric Force and Newton's Third Law This electric force exerted between two charged objects is a force in the same sense that friction, tension, gravity and air resistance are forces. And being a force, the same laws and principles that describe any force describe the electrical force. One of those laws was Newton's law of action-reaction. (balloons) Force of D upon C is the same in magnitude as Force of C upon D. they are action and reaction forces. Force of B upon A is the same in magnitude as Force of A upon B. they are action and reaction forces.

11. Interaction Between Charged and Neutral Objects Any charged object - whether positively charged or negatively charged - will have an attractive interaction with a neutral object. Positively charged objects and neutral objects attract each other; Negatively charged objects and neutral objects attract each other. Any charged object - plastic, rubber, or aluminum - will exert an attractive force upon a neutral object. And in accordance with Newton's law of action-reaction, the neutral object attracts the charged object.

12. Charge detection If two objects repel each other… one can conclude that both objects are charged and charged with the same type of charge. One could not conclude that the balloons are both positively charged or both negatively charged. If two objects attract each other… one can conclude that at least one of the objects is charged. The other object is either neutral or charged with the opposite type of charge. You cannot draw a conclusion about which one of the objects is charged or what type of charge (positive or negative) the charged object possesses.

13. Example A lightweight sphere hangs by an insulating thread. A student wishes to determine if the sphere is neutral or electrostatically charged. She has a negatively charged hard rubber rod and a positively charged glass rod. She does not touch the sphere with the rods, but runs tests by bringing them near the sphere one at a time. The student notes that the sphere is attracted to both rods. This test result shows that the charge on the sphere is positive negative neutral

14. Example A negatively charged plastic comb is brought close to, but does not touch, a small piece of paper. If the comb and the paper are attracted to each other, the charge on the paper may be negative or neutral may be positive or neutral must be negative must be positive

15. Electric charge is quantized: Millikan Oil Drop Experiment: The experiment determined that the charge on an object is always a multiple of a fundamental unit of charge, symbolize by e

16. Definitions • charge: a fundamental property of matter • measured in COULOMBS or ELEMENTARY CHARGE • charge on an object is carried by particles • Electron • -1.6 x 10-19 coulombs • -1e • Proton • +1.6 x 10-19 coulombs • +1e The units of micro-Coulombs (1 µC = 10-6 C) or nano-Coulombs (nC = 10-9 C) are more commonly used as the unit of measurement of charge.

17. Charged Objects Because objects can only gain or lose electrons, the only charges that are allowed are multiples of the ELEMENTARY CHARGE This plate is neutral – number of protons = number of electrons If the plate loses one electron If the plate loses two electrons If the plate loses three electrons Its charge becomes… Its charge becomes… Its charge becomes… +2 e Or +3.2 x 10-19 Coulombs +3 e Or +4.8 x 10-19 Coulombs +1e Or +1.6 x 10-19 Coulombs The plate has a LACK OF ELECTRONS +1 Elementary Charge +2 Elementary Charges +3 Elementary Charges

18. Example #1 • An object has three excess electrons. • What is its “elementary charge”? • What is its charge in coulombs? -3e q = -3e x (1.6 x 10-19 C)/e = -4.8 x 10-19 C

19. Example #2 • An object has 75 protons and 65 electrons • What is its “elementary charge”? • What is its charge in coulombs? +10 e q = +10e x (1.6 x 10-19 C)/e = +16 x 10-19 C

20. Law of Conservation of Charge • The total amount of charge in a closed system remains constant – charge is not created or destroyed, it only moves from one object to another • Charge “moves” as a result of ELECTRONmovement ONLY!!!

21. Example #3 • A metal sphere with two excess electrons touches a neutral metal sphere and then taken away. • What do you predict the charge on each sphere will be after they make contact? • What is the total charge on both spheres after they come in contact? -1e or -1.6 x 10-19 C -2e or -3.2 x 10-19 C The TOTAL CHARGE remains the SAME!!!

22. 2/6 do now • The graph below represents the motion of a car during a 6.0-second time interval. • What is the velocity during 4.0 – 6.0 s interval? • What is the acceleration during 0.0 – 4.0 s interval? • What is the total distance traveled by the car during this 6.0-second interval?

23. Objectives • Understand the basic properties of electric charge. • Differentiate between conductors and insulators. • Distinguish between charging by contact and charging by polarization. Homework: Castle learning: you have two days to do. If you did not finish in time, you can come post session to make up homework.

24. Recap • What is it that gives objects a charge? • What are some interactions between charges? • What did Miliken’s oil drop experiment determine? • How is it charge measured? • What is the relationship between fundamental charge and charge in coulombs. • What does the Law of Conservation of Charge tell us?

25. question • A negative charged sphere is placed near a neutral sphere. Which graph represents charge distribution on the neutral sphere? - - - - + - - + + - + - A. B. - - - - - + - + C. D.

26. Restless Electrons 4.1.2 Transfer of Charge

27. Conductive Properties of Materials NbTi alloy metals wood silicon rubber pure water sea water HIGH CONDUCTIVITY LOW CONDUCTIVITY LOW RESISTIVITY HIGH RESISTIVITY Good Conductor/ Poor Insulator Allows electrons to flow freely. Good Insulator/ Poor Conductor Strongly resists flow of electrons. The division of materials into the categories of conductors and insulators is a somewhat artificial division. It is more appropriate to think of materials as being placed somewhere along a continuum.

28. insulators vs. conductors charge on a conductor is quickly distributed across the entire surface of the object. Why do think this happens? • Charge on an insulator will remain at the initial location of charging. The insulating cups are use to prevent charge from escaping to the surroundings as well as to provide for a convenient handle.

29. Examples of conductors and insulators • Examples of conductors include • metals, • aqueous solutions of salts • graphite, • water • human body. • Examples of insulators • plastics, • Styrofoam, • paper, • rubber, • glass • dry air.

30. Human body is a conductor • Along the continuum of conductors and insulators, one might find the human body somewhere towards the conducting side of the middle. When the body acquires a static charge it has a tendency to distribute that charge throughout the surface of the body. • phet

31. Water is a conductor • Water, being a conductor, has a tendency to gradually remove excess charge from objects. Since humidity levels tend to vary from day to day and season to season, it is expected that electrical affects (and even the success of electrostatic demonstrations) can vary from day to day.

32. Distribution of Charge via Electron Movement • Predicting the direction that electrons would move within a conducting material is a simple application of the two fundamental rules of charge interaction. Opposites attract and likes repel. • The excess negative charge distributes itself throughout the surface of the conductor. This is because electrons wish to manipulate their surroundings in an effort to reduce repulsive affects.

33. Check your understanding • Suppose that a conducting sphere is charged positively by some method. The charge is initially deposited on the left side of the sphere. Yet because the object is conductive, the charge spreads uniformly throughout the surface of the sphere. The uniform distribution of charge is explained by the fact that ____. a. the charged atoms at the location of charge move throughout the surface of the sphere b. the excess protons move from the location of charge to the rest of the sphere c. excess electrons from the rest of the sphere are attracted towards the excess protons

34. Charging by friction • When two objects are rubbed together electrons may be transferred from one object to another. One object gains electrons and the other object loses electrons, so both objects have a charge. • Charging by friction results opposite charges on the two objects rubbed together.

35. Charging by Friction • Rub two insulators together • ELECTRONSmove from one to the other • One object becomes + the other - RULE #1 – ONLY ELECTRONS MOVE

36. When wool is rubbed against a PVC pipe, the PVCsteals electrons from the wool because it has higher electron affinity compared to wool. The PVC strip ends up with a negative charge while the wool ends up with a positive charge When wool is rubbed against a Nylon strip, the wool will steal electrons from the Nylon because wool has higher electron affinity than Nylon.  As a result, the Nylon ends up positively charged and the wool ends up negative.

37. How do we know which object will gain electrons and which will lose electrons? • electron affinity determines which object will gain electrons. • The property of electron affinity refers to the relative amount oflove that a material has for electrons. High affinity means the material has more pull to electrons. • The more love of electrons a material has the more likely it is to steal electrons from the other object during charging by friction

38. 2/7 do now • When a neutral metal sphere is charged by contact with a positively charged glass rod, the sphere • loses electrons • loses protons • gains electrons • gains protons • Explain you answer

39. Objectives • Understand the basic properties of electric charge. • Differentiate between conductors and insulators. • Distinguish between charging by contact and charging by polarization. • Homework: • Castle learning • Text book - Page 633 #1-6

40. Triboelectric series • A triboelectric series is an ordering of substances with high affinities on top. • When any two materials in the table are rubbed together, the one which is higher can be expected to pull electrons from the material which is lower. Metal can also be charged by friction

41. Law of Conservation of Charge The total amount of charge in a closed system remains constant – charge is not created or destroyed, it only moves from one object to another The frictional charging process (as well as any charging process) involves a transfer of electrons between two objects. During all charging processes, the net charge of the system is conserved.

42. Charging by Conduction Charging by conduction involves the contact of a charged object to a neutral object. Upon contact, e- move from the sphere to the electroscope and spread about uniformly. A metal sphere with an excess of – charge is brought near to a neutral electroscope. The metal sphere now has less excess – charge and the electroscope now has a - charge

43. When charging by conduction both object have the same type of charge when separated. If A negatively charged object touches a neutral object the neutral object gains electrons and becomes negatively charged as well. If a positively charged object touches a neutral object then the neutral object loses electrons and when separated it is positively charged as well. To charge by conduction successfully your charged and neutral object must be conductors!

44. Law of Conservation of Charge In a closed system, charge is always conserved. The total amount of charge among the objects is the same before the charging process starts as it is after the process ends.

45. example Two metal spheres having charges of +4.0 × 10-6 coulomb and +2.0 × 10-5 coulomb, respectively, are brought into contact and then separated.  After separation, the charge on each sphere is 8.0 × 10-11 C 8.0 × 10-6 C 2.1 × 10-6 C 1.2 × 10-5 C

46. Castle learning questions • A joule is equivalent to a • N•m • N•s • N/m • N/s • Kg∙m2/s2 • There could be more than one answer.

47. Polarization - Why a charged object attract neutral object • In an atom, the protons are tightly bound in a nucleus and incapable of movement. In conducting objects, electrons are so loosely bound that they may be induced into moving from one portion of the object to another portion of the object. • By placing a charged object near a neutral conducting object you can create electron movement.

48. No electrons have been added to or subtracted from the can yet there is a charge at either end of the can; overall the can is electrically neutral. This arrangement of charge is called polarization.

49. Polarization is the process of separating opposite charges within an object. • The polarization process always involves the use of a charged object to induce electron movement or electron rearrangement. • By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites. • Polarization is not charging – the total charge in a polarized object is still zero just like before.

50. A surface charge can be induced on insulators by polarization • In an insulator, electrons merely redistribute themselves within the atom or molecules nearest the outer surface of the object.