1. They’re Attractive & Repulsive at the Same Time

2. When two charges are brought together they either push away from each other or they pull towards each other. + + - - Since the charges will change their motion, Newton’s First Law tells us they must have a force applied to them!!!! Newton’s Third Law tells us that the force on each charge must be equal in size but opposite in direction. They are an action-reaction pair!!!! If there is no net force acting on an object, then

3. Electric Charge  We know that there are two types of charge – positive and negative.  We know that protons are 2000 times bigger than electrons in terms of mass.  We know that even though protons are positively charged & electrons are negatively charged, protons and electrons carry the same size charge.  The size of the charge on a proton & an electron is defined in units called a Coulomb (C).  A Coulomb (C) is the unit used to measure electric charge.

4. Electric Charge  A Coulomb of charge is very large.  It would take 6.25 X 10 18 protons to make 1-C of charge.  For those of you who avoid scientific notation like the plague: It takes 6,250,000,000,000,000,000 protons to make 1-C of charge.  A proton has a charge of 1.6 X 10 -19 -C, an electron has a charge of -1.6X 10 -19 -C.  For you anti-plague people: 1.6 X 10 -19 -C = 0.000 000 000 000 000 000 16-C Particle Charge (C) Mass (kg) Proton1.60 x 10 -19 1.673 x 10 -27 Electron-1.60 x 10 -19 9.109 x 10 -31 Neutron01.675 x 10 -27

5. Coulomb’s Law In 1875, Charles Coulomb did some experiments on the forces between electric charges. He discovered two things: 1) The size of the force depends directly with the product of each charge.. F E ~ Q 1 ∙Q 2 Where Q is the size of the charge in Coulombs. 2) The size of the force depends inversely with the square of the distance between the charges. F E ~ 1/r 2 Where r is the distance between the charges.

6. Example Find the electrical force between a 1-C charge and a 3-C charge that are 6-m apart. KnowFormula Work Q 1 = 1-C Q 2 = 3-C r = 6-m The (+) answer means the force is repulsive – LIKE CHARGES REPEL

7. Example 2 Find the electrical force between a 5-C charge and a -5-C charge that are 100-m apart. KnowFormula Work Q 1 = 5-C Q 2 = -5-C r = 100-m The (-) answer means the force is attractive – opposite CHARGES attract