II. Two of the 4 fundamental forces: 1. The _____________________ force, F g, between 2 masses: 2. The _______________________ force, F e, between two charges F g = …is always ______________________ …is ___________________________ to the masses …is ______________proportional to ____________ of r …is _______________, which can be seen because the constant G = __________________________ is __________. F e = attractive gravitational directly proportional very weak 6.67 x N·m 2 /kg 2 tiny electrical ??? the squareinversely Gm 1 m 2 r 2

Suppose two charges q 1 and q 2 repel each other with an electrical force F e =___. Then experiments are done… Exp. #using….and…. separated by a distance… new F e 1q1q1 2q q 1 q2q2 1 32q 1 3q 2 1 4q1q1 q2q2 2 5q1q1 q2q2 3 6q1q1 q2q2 4 What can you conclude about the form of the electrical force? It is directly proportional to the _____________ on each object, and ___________ proportional to the ____________________ _______________________________ /4 10/9 charge square of the distance between the two charges. 10/16 10 inversely

Coulomb’s Law: The electrostatic force, F e, between two charges q 1 and q 2 separated by a center-to-center distance r is… F e = where k = ________________________________ = ________________________________ ________________________________ q1q1 q2q2 r

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Coulomb’s Law: The electrostatic force, F e, between two charges q 1 and q 2 separated by a center-to-center distance r is… F e = where k = ________________________________ = ________________________________ ________________________________ q1q1 q2q2 r kq 1 q 2 r 2

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Coulomb’s Law: The electrostatic force, F e, between two charges q 1 and q 2 separated by a center-to-center distance r is… F e = where k = ________________________________ = ________________________________ ________________________________ q1q1 q2q2 r 8.99 x 10 9 N · m 2 /C 2, with q in coulombs and r in meters the electrostatic constant kq 1 q 2 r 2

French physicist Charles-Augustin de Coulomb

Ex: Cavendish "Weighing the Earth" Experiment: m1m1 thin wire Pb barbells When a ____ sphere (m 2 ) was brought close to the barbells, the _______________ attraction caused the thin wire to _________. Then F g, r, m 2 and m 1 were substituted into: Pb twistestimated G m 1 m 2 r 2 F g = and this was solved to find ______. r gravitational From the wire's properties, the ______________ needed to make the wire twist that much could be _____________ force, F g G m R e 2 w = G G MeMe Earth's m2m2 Once _____ was known, an object of known mass m and weight w were used to find ___________ unknown mass M e using

Coulomb’s torsion (twisting) balance:

Ex: Coulomb “charge" Experiment:` q1q1 silk thread counterweight When a charged ball q 2 was brought close to the charge q 1, the _______________ attraction caused the thin wire to _________. twist k q 1 q 2 r 2 F e = and this was solved to find k. r electrical From the thread’s twisting, the ______________ needed to make the wire twist that much could be determined. force, F e q2q2

Note: 2. F e is ___________________ if the charges are “opposite” and_____________________ if the charges are “like” 4. F e is an ________________________________force. 1.F e is… …directly proportional to ____________ …and inversely proportional to ______ 3. F e is ___________stronger than the gravitational force because ________ is ____________________ than ______. “at a distance” MUCH k G repulsive attractive the q’s r2r2 MUCH greater FeFe FeFe q r FeFe m

Ex: Find the electrical force between two charges q 1 = +3.4 x C and q 2 = -1.7 x C whose centers are separated by a distance of 2.5 x m. Is the force attractive or repulsive? Which charge exerts a stronger force? If released from rest, which would accelerate more? kq 1 q 2 r 2 F e = ( 8.99 x 10 9 N · m 2 /C 2 ) (+ 3.4 x C ) (- 1.7 x C ) ( 2.5 x m ) 2 F e = (- 5.2 N · m 2 ) ( 6.25 x m 2 ) = N attractive neither You can’t tell, since the masses are not given.

Ex: Two _______________ masses: FgFg The same two masses with ___________ charges: FgFg FgFg FgFg The same two masses but with _______________ charge: FeFe FeFe FeFe FeFe FgFg FgFg neutral like opposite

Ex: Because gravity and the electrostatic force are ____ ____________ … ___________ holds the planets to the Sun (S): S v FgFg The ____________ force binds electrons to the nucleus (N): N v FeFe planet electron Gravity electrical It was thought that the electrostatic force was responsible for allowing the electron to ____________________________. so similar orbit the nucleus

1. Electrons in circular orbits ___________________. 2. Accelerating charges ______________________. 3. Therefore, orbiting electrons would ________ energy and _________________________________ and all matter would ___________________in a fraction of a second A better theory was needed, so _______________________ was developed. It says that: 1. The electron _______________________, but ___________________________ orbit. 2. The “orbit” only tells you where the electron is ____________________ to be found or the _____________________ of finding it somewhere! In reality, orbiting electrons ______________________ Why? are not possible! are accelerating radiate energy away lose spiral into the nucleus collapse quantum mechanics does not orbit occupies a “stationary” most likely probability

The electron "cloud" is the modern idea of an electron. Brighter areas are where the electron is more likely to be found, i.e., has a higher probability of being found. The electron does not "move around." lowest energy "orbit" higher energy "orbits"

Electron "cloud" is _________ where the electron is _______ _________ to be found. The ________ ____________ are spread out around in the cloud. Electron cloud model: = __________ densest most likely nucleus charge and mass __________ electron cloud