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.]

1. a-t2. v-t3. d-t

• 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

2/4 do now• A cart travels with a constant nonzero

acceleration along a straight line. Graph the following relationships:

1. Acceleration vs. time2. Velocity vs. time3. Distance vs. time

Objectives1. Understand the basic properties of electric

charge.2. Differentiate between conductors and

insulators.3. 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.

Atomic Structure ReviewMatter is made up of small structures called ATOMSAt the center of each atom is a NUCLEUSWithin the NUCLEUS are two types of NUCLEONS

PROTONS NEUTRONS

POSITIVE CHARGE

DO NOT MOVEWITHIN MATTER

NO CHARGE – NEUTRAL

DO NOT MOVEWITHIN MATTER

Orbiting the NUCLEUS are ELECTRONS

ELECTRONS

NEGATIVE chargeOrbit nucleus

Charged ObjectsObjects 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.

Example

• Which part of an atom is most likely to be transferred as a body acquires a static electric charge?

1. proton 2. neutron 3. electron 4. positron

• 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.

Example

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:1. Opposites attract. 2. likes repel.

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 B upon A is the same in magnitude as Force of A upon B. they are action and reaction forces.

Force of D upon C is the same in magnitude as Force of C upon D. they are action and reaction forces.

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.

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.

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

1. positive 2. negative 3. neutral

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

1. may be negative or neutral 2. may be positive or neutral 3. must be negative 4. must be positive

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

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.

Charged Objects

This plate is neutral – number of protons = number of electrons

If the plate loses one electron

Its charge becomes…

+1eOr

+1.6 x 10-19 Coulombs

+1 Elementary Charge

If the plate loses two electrons

+2 eOr

+3.2 x 10-19 Coulombs

+2 Elementary Charges

Its charge becomes…

If the plate loses three electrons

+3 eOr

+4.8 x 10-19 Coulombs

Its charge becomes…

+3 Elementary Charges

Because objects can only gain or lose electrons, the only charges that are allowed are multiples of the

ELEMENTARY CHARGE

The plate has a LACK OF ELECTRONS

• 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

Example #1

• 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

Example #2

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 ELECTRON movement ONLY!!!

• 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!!!

Example #3

2/6 do now• The graph below represents the motion of a car during a

6.0-second time interval. 1. What is the velocity during 4.0 – 6.0 s interval?2. What is the acceleration during 0.0 – 4.0 s interval?3. What is the total distance traveled by the car during this

6.0-second interval?

Objectives1. Understand the basic properties of electric

charge.2. Differentiate between conductors and

insulators.3. 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.

Recap

1. What is it that gives objects a charge? 2. What are some interactions between charges?3. What did Miliken’s oil drop experiment determine?4. How is it charge measured? 5. What is the relationship between fundamental charge

and charge in coulombs. 6. What does the Law of Conservation of Charge tell us?

question• A negative charged sphere is placed near a

neutral sphere. Which graph represents charge distribution on the neutral sphere?

- -

- -

+ -- +

+ -+ -

- +- +

- -- -

A. B.

C. D.

Restless Electrons

4.1.2 Transfer of Charge

Good Conductor/Poor Insulator

Allows electrons to flow freely.

Good Insulator/Poor Conductor

Strongly resists flow of electrons.

rubber

silicon

wood

pure water

metals

NbTi

alloy

sea water

Conductive Properties of Materials

HIGH CONDUCTIVITY LOW CONDUCTIVITY LOW RESISTIVITY HIGH RESISTIVITY

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.

Charge on an insulator will remain at the initial location of charging.

charge on a conductor is quickly distributed across the entire surface of the object. Why do think this happens?

The insulating cups are use to prevent charge from escaping to the surroundings as well as to provide for a convenient handle.

insulators vs. conductors

Examples of conductors and insulators• Examples of insulators

– plastics, – Styrofoam, – paper, – rubber, – glass – dry air.

• Examples of conductors include – metals, – aqueous solutions of

salts – graphite, – water– human body.

• 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

Human body 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.

Water is a conductor

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.

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

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.

Charging by Friction• Rub two insulators together

• ELECTRONS move from one to the other• One object becomes + the other -

RULE #1 – ONLY ELECTRONS MOVE

When wool is rubbed against a PVC pipe, the PVC steals electrons from the wool because it has higher electron affinity compared to wool. The PVC strip ends up with a negative charge while the woolends 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.

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 of love 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

2/7 do now

• When a neutral metal sphere is charged by contact with a positively charged glass rod, the sphere

1. loses electrons2. loses protons3. gains electrons4. gains protons• Explain you answer

Objectives1. Understand the basic properties of electric

charge.2. Differentiate between conductors and

insulators.3. Distinguish between charging by contact

and charging by polarization.

Homework:1. Castle learning2. Text book - Page 633 #1-6

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

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.

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.

The metal sphere now has less excess – charge and the electroscope now has a - charge

A metal sphere with an excess of – charge is brought near to a neutral electroscope.

• 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!

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.

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

1. 8.0 × 10-11 C 2. 8.0 × 10-6 C 3. 2.1 × 10-6 C 4. 1.2 × 10-5 C

Castle learning questions• A joule is equivalent to a1. N•m2. N•s3. N/m4. N/s5. Kg m∙ 2/s2

• There could be more than one answer.

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.

• 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.

• 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.

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.

Polarization is Not Charging

• When an object becomes polarized, there is simply a redistribution of the centers of positive and negative charges within the object.

• While there is a separation of charge, there is NOT an imbalance of charge. When neutral objects become polarized, they are still neutral objects.

example

• An inflated balloon which has been rubbed against a person's hair is touched to a neutral wall and remains attracted to it. Which diagram best represents the charge distribution on the balloon and the wall?

a b c d

example

• The diagram below shows three neutral metal spheres, x, y, and z, in contact and on insulating stands. Which diagram best represents the charge distribution on the spheres when a positively charged rod is brought near sphere x, but does not touch it?

A B

C

D

The Electroscope • An electroscope is a device which is capable of detecting the

presence of a charged object through polarization.

Polarization of an electroscope

- - - - -

-

-

-

-

Grounding Symbol:

Grounding

• Since the Earth is very large it can neutralize:• negative objects by

ABSORBING electrons• positive objects by

RELEASING electrons

++++

RULE #2 – GROUNDING MAKES ANOBJECT NEUTRAL

Charging by Induction• charging by induction method is to charge an object

without actually touching the charged object.

• Charging by induction requires conductor, polarization, and grounding.

Charging by induction using two conductors

Charging a single sphere by induction

The Importance of a Ground in Induction Charging

• In the charging by induction cases, charge is never transferred from the charged object to the neutral object… They do not touch! The charged object causes the neutral object to become polarized.

• The neutral object got charged through a ground.

• A ground can serve as a supplier or receiver of electrons.

Examples of ground

ground

ground

Grounding is also a way of uncharging an object.

The Need for a Conducting Pathway• Any object can be grounded provided that the charged atoms

of that object have a conducting pathway between the atoms and the ground.

Electrons will travel along that pathway.

Charging an electroscope by induction

1. Bring a charged object near the electroscope

2. The electroscope is being polarized.

3. Touch the part of the electroscope that is away from the charged object.

4. Remove your hand.

5. Remove the charged object.

fundamental principles regarding induction charging

1. The charged object is never touched to the object being charged by induction.

2. The charged object does not transfer electrons to or receive electrons from the object being charged. The charged object serves to polarize the object being charged.

3. The object being charged is touched by a ground; electrons are transferred between the ground and the object being charged (either into the object or out of it).

4. The object being charged ultimately receives a charge that is opposite that of the charged object which is used to polarize it.

example

• A charged body may cause the temporary redistribution of charge on another body without coming in contact with it. This process is called

1. conduction 2. potential 3. Charging by friction 4. induction

Extra practice

1. An object can not have a charge ofa. 3.2 × 10-19 C b. 4.5 × 10-19 C c. 8.0 × 10-19 C d. 9.6 × 10-19 C

2. What is the smallest electric charge that can be put on an object?

a. 9.11 × 10-31 C b. 1.60 × 10-19 C c. 9.00 × 109 C d. 6.25 × 1018 C

Example

• What is the net charge of an object possessing an excess of 6.0 x 106 electrons?

Example – change electrons to Coulomb

(6.0 · 106 e)(1.60 · 10-19 C/e) = 9.6 x 10-13 C

Since there are 1.6 · 10-19 Coulomb in 1 electron, you can multiply the number of electrons by 1.6 · 10-19 Coulomb to find the result.

• A metal sphere has a net negative charge of 1.1 x 10-7 coulomb. How many more electrons than protons are on the sphere?

(1.1 · 10-7 C)(6.25 · 1018 e/C) = 6.875 x 1011 e

Since there are 6.25 · 1018 electrons in 1 Coulomb, you can multiply the number of Coulomb by 6.25 x 1018 electrons to the result. x = 6.875 x 1011 e

Example – change Coulomb to electrons

example• If an object possessing an excess of 6.0 × 106 electrons, what

is its charge in Coulombs?

• Which quantity of excess electric charge could be found on an object?

1. 0.25 elementary charges 2. 5.25 × 10-19 C 3. 6.40 × 10-19 C 4. 1.60 elementary charges

7.1 Characteristics of uniform circular motion1. What is uniform circular motion? 2. Describe the magnitude and the direction of velocity of a uniform

circular motion.3. Describe the magnitude and the direction of acceleration of a

uniform circular motion.4. Describe the magnitude and the direction of net force of a

uniform circular motion.5. What does centripetal mean?6. Why is force required when an object moves in a circle?7. How is centripetal force related to mass, velocity and radius of the

object moving in a uniform circular path? Give examples to show your understanding.

7.3 The law of universal gravitation

1. What is inverse squared relationship? Give examples to show your understanding.

2. What does “universal” in the law of universal gravitation mean?3. What is gravity?4. Write the equation of universal gravitation and indicate each

symbol in the equation mean. Draw a picture to show your understanding.

5. How is gravitational force related to masses of each object and how is it related to the distance from the center of each mass? Give examples to show your understanding.

6. How is value g related to the distance from the center of Earth?7. Draw a picture to illustrate that gravity is a field force.

Lab 14

• Static electricity station lab

1/30 do now• 1) A metallic sphere gains 500 electrons. a. Determine the amount of ‘elementary charge’ that is

now on the sphere. Be sure to indicate positive or negative!

b. Calculate the charge on the sphere in coulombs.

End of 5.1.1 - PRACTICE

objectives• Know:

– Definition of insulator, conductor– Charge is transferred in solids by electron movement only.

• Understand: - How charge is transferred by contact and induction - How surface charge can be induced on insulators by

polarization.

• Be able to: - Explain how charged object attract neutral objects