Vector quantity Magnitude numerical quantity Direction Net Force

• Vector quantity – Magnitude (numerical quantity) – Direction • Net Force – unbalanced forces cause motion – balanced forces keep objects at rest • Types of Forces – Contact forces like normal or tension – Field forces, like gravity (field = “acts at a distance”)

è All matter is made of atoms è Atoms have 3 basic parts: – positively charged protons (+) – negatively charged electron (-) – neutral (no charge) neutrons (0) è Electric charge is a fundamental property of matter! è Electrons have the smallest mass, thus they are the only subatomic particle that can move from one atom/object to the next (if the right conditions are present)

• Caused by positive and negative charges

• Electric Force is the attraction or repulsion between objects – can cause a change in motion • Is a field force because it “acts at a distance” FORCE DIAGRAMS

• Exist in the region surrounding charged particles or objects • Represented by lines of force – Start at positive charges – End on negative charges • Strongest near the object

Consider the electric field lines drawn at the right for a configuration of two charges. Several locations are labeled on the diagram. Rank these locations in order of the electric field strength - from smallest to largest.

• Quantifies the electric force between 2 charged objects that are at some distance apart. – a Coulomb (C) is the SI unit of charge • 1 C = 6. 24 x 1018 Newtons (N) • The charge on one electron or proton = (+/-)1. 6 x 10 -19 C • Called the “elementary charge” • Symbolized by q 0 • Formula: – k is coulomb’s law constant=8. 99 x 109 N-m 2/C 2 – Q 1 and Q 2 are the charges of each object – d is the distance between the objects

Determine the magnitude of electrical force of attraction between two balloons with separate charges of +3. 5 x 10 -8 C and 2. 9 x 10 -8 C when separated a distance of 0. 65 m.

A young woman (m=55 kg) accumulates a charge of +2 x 105 C while sliding out of the front seat of her car. Her boy friend (m=80 kg) has been standing in the wind and has accumulated a charged of -8 x 10 -5 C. F Calculate the magnitude of electrical force the woman exerts on her boyfriend when they are 0. 5 m apart. F= k. Q 1 Q 2/d 2

F= k. Q 1 Q 2/d 2 F= (8. 99 x 109)(+2 x 10 -5)(-8 x 10 -5)/(0. 5)2 F= 57. 54 N F

How does the magnitude of the force the boyfriend exerts on the woman compare to the magnitude of the force the woman exerts on her boyfriend. F

Determine the magnitude of electrical force between two protons in nucleus of helium atom when separate by 2. 0 x 10 -15 m. . F F= k. Q 1 Q 2/d 2

F= k. Q 1 Q 2/d 2 F= (8. 99 x 109)(+1. 6 x 10 -19)/(2 x 10 -15)2 F F= 57. 5 N

A cell membrane has a positive charge of 1. 6 x 10 -19 C on the outside wall and negative charged of -1. 6 x 10 -19 C on the inside wall. Calculate the magnitude of electrons of electrical force between these two ions if F the membrane thickness is 8 x 10 -10 m. F= k. Q 1 Q 2/d 2

F= k. Q 1 Q 2/d 2 F= (8. 99 x 109)(1. 6 x 10 -19)(-1. 6 x 10 -19)/(8. 0 x 10 -10)2 F= 3. 59 x 10 -10 N F

• Force between the objects is: – directly proportional to the product of their charges (Qx. Q) – inversely proportional to the distance squared between them F∽C

• Follows the Inverse Square Law • If distance between 2 objects is doubled, what happens to the force between them? ∽ The magnitude of electrical force between two particles is 10 N. • If distance between 2 objects is halved, what happens to the force between them? ∽

F∽ • If charge of one object is halved, what Cforce between the happens to the The magnitude of electrical force between two particles is 10 N. objects? ∽ ∽ • If the charge of one object is doubled, what happens to the force? ∽ ∽

• How are these Laws the same? – Both concern field forces between objects – Both have a constant value – Both follow the inverse square law • How are these Laws different? – Gravitational force can only be attractive – Electrical force can be attractive or repulsive

Study of electric charge “at rest” within objects

Positive electric charges a. b. c. d. attract both positive and negative charges. repel both positive and negative charges. attract positive and repel negative charges. repel positive and attract negative charges.

A beam of electrons is directed into the electric field between two oppositely charged parallel plates, as shown in the diagram below. The electrostatic force exerted on the electrons by the electric field is directed a. into the screen. b. out of the screen. c. toward the bottom of the screen. d. toward the top of the screen.

A beam of electrons is directed into the electric field between two oppositely charged parallel plates, as shown in the diagram below. What is the direction of the electric field in the above situation? a. into the screen. Different b. out of the screen. Question c. toward the bottom of the screen. d. toward the top of the screen.

The diagram below shows two identical metal spheres, A and B, separated by distance d. Each sphere has mass m and possesses charge q. Which diagram best represents the electrostatic force Fe and the gravitational force Fg acting on sphere B due to sphere A?

Electrostatics is defined as the study of electric charge at rest within objects. (static electricity) John Travoltage – It is the accumulation of charge, followed by a rapid discharge Gas Station Flash Fire How do objects become charged? – Charges within objects can become separated, due to the movement of electrons • Neutral atoms/objects have equal protons and electrons • Charged atoms/objects have more or less electrons compared to it’s number of protons

Remember, the only subatomic particle that can move from one atom/object to another is the electron – An object that: • Gaining electrons, will result in a negative charge • Loses electrons, will result in a positive charge

Neutral sample Object -8 Net Charge: +8 0 Charged sample Object -6 Net Charge: +8 +2

The most common way for a negative pith ball to become neutral is for it to a. b. c. d. gain some electrons. lose some electrons. gain some protons. lose all its electrons.

Conductors: metals, aqueous solutions of salts (i. e. , ionic compounds dissolved in water), graphite, water, and the human body. Electrons will move differently, depending on the kind of Insulators: plastics, styrofoam, paper, rubber, glass, and dry air. material they are moving within • In conductors: electrons are “free” & can move throughout the material in good conductors, can move from atom to atom & object to object • In Insulators: do not allow free movement of electrons throughout the material, or from the object to other things

Semiconductors are found in microprocessor chips, transistors, and anything that's computerized or uses radio waves depends on semiconductors

A pure silicon crystal is nearly an insulator Doping Silicon Changing the behavior of silicon mixing a small amount of an impurity into the silicon crystal. N-type - phosphorus or arsenic is added to the silicon. Both have five outer electrons, so they're out of place when they get into the silicon lattice. In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons to conduct electric current. P-type - boron or gallium are added. Each have only three outer electrons. They form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over a space.

*net charges must equal • Within objects: zero* Negative Pole – If part of an object becomes positive (or negative), the other part of an object must become equally but oppositely charged – Example: water molecules Positive Pole

*net charges must equal zero*

• Between interacting objects – If an object becomes charged from interacting with another, the other object must become equally, but oppositely charged. Static Electricity Balloon Phet

Net charge: 0 Balloon net charge: – 10 Net charge: 0 Sweater net charge: +10 Net overall charge: 0

#1: Friction – Electrons transferred between two neutral objects by rubbing 2 them together

Charging by Friction • Friction creates oppositely charged objects. The net charge of both together is zero.

Triboelectric Series Different materials have different affinities for electrons. More likely to lose electrons (+) Human hands (when dry) Leather Rabbit fur Glass Human hair Wool Silk Paper Amber Brass Silver Polyester Sytrofoam Scotch tape PVC • Rubbing amber with silk causes electrons from the silk to move to the amber • Rubbing glass with silk causes electrons to move from the glass to the silk More likely to gain electrons (-)

Which has the greatest affinity for electrons? Teflon

When amber is rubbed on a piece of silk, what happens? a. Electrons are transferred from the amber to the silk. b. Electrons are transferred from the silk to the amber. c. Protons are transferred from the amber to the silk. d. Protons are transferred from the silk to the amber.

#2: Conduction John Travoltage – Occurs when a charged object transfers it’s electron to a neutral object, by coming into direct contact pith ball simulation with it. (touching)

Step 1: Objects are brought close together Step 2: They touch

Step 3: Electrons are transferred from the charged to the neutral object Step 4: Both objects are now charged

Sharing Charge via Conduction • A metal sphere (A) with a charge of +4 units is brought in contact with a metal sphere (B) with -2 units of charge, and the spheres are then separated. What is the charge on each sphere after separation? + + +4 +- +-2 A B + - + + +-+ - + + + - Electrons evenly distribute. +- ++1 A +- + + - ++1 B A B Charges will be equal!

#3: Polarization – Surface charge (object remains neutral, overall) – Charges within object shift • in response to being near a charged object • Only exists while near the charged object

Lightning

èCaused by the buildup of electrical charge in clouds (due to the friction caused by the movement of water droplets) i. ii. Bottom is usually negative, and the top positive This accumulation repels negative charges in the ground, leaving the surface of the ground positive èAs the charge increases, a bolt of many billions of electrons are transferred at the same time to the Earth. èThis is followed by a streamer of positively charged air particles that is repelled by the ground that travels back upwards èLightning bolts ionize the atoms in the air producing great amounts of heat, causing compressional waves (sound) called thunder.

#4: Induction – Starts similar to polarization – Two neutral objects in contact (a) – A third, charged object brought near to polarize them (b) – The now polarized objects are separated – And now the objects are themselves charged

Leyden Jar Stores electrical charge using an insulator between two conductors

Grounding phet - travolta

Van de Graaff Generator Generates large amounts of static electricity, using a moving rubber belt (FRICTION!!!)

Van de Graaff Generator and Pie Pans

How a Van de Graaff Generator Works: Van de Graaff video Van de Graaff explanation losing charge

Charge… Discharge!!! 59

Electroscope electroscope simulations

The Electroscope èmade of two thin metal leaves attached to a metal rod with a knob at the top. - when the device is not charged, the leaves hang straight down. - when an electric charge is present, the leaves repel each other, spreading apart.

Closure on Static Electricity èWhat èWhat are the charged particles in an atom? is the rule of electric charges? causes an electric charge? is static electricity? is static discharge? would happen if a lightning rod were made of an insulator rather than a conductor?