CHARGING BY FRICTION REVIEW! EXAMPLE: Amber and wool are rubbed together. Note: From now on, our electric charge diagrams will need to be accurate. That is, if we start off with 6 electrons and 6 protons TOTAL in BOTH materials, we must end up with the same TOTAL number in the result diagram. This is due to Conservation of Charge: The net charge of an isolated system remains constant.

IMPORTANT NOTE ON LAWS OF ELECTRIC CHARGE RECALL: A positively charged object will be attracted to a neutral object because the neutral object is more negative than the positively charged object. (Recall neutral objects contain equal numbers of protons and electrons) BUT ALSO:

PRACTICE – GET OUT YOUR MC CARDS! 1. What happens when two neutral objects made out of different materials are rubbed together? a) the material lower on the electrostatic series loses protons to material higher on the list b) the material higher on the electrostatic series gains protons from material lower on the c) the material higher on the electrostatic series lose electrons to the material lower on the list d) the material lower on the electrostatic series lose electrons to the material higher on the list.

PRACTICE – GET OUT YOUR MC CARDS! 2. What happens if the two neutral objects made of the same material are rubbed together? a) one object gains all of the other object’s electrons b) one object gains all of the other object’s protons c) nothing – they both remain neutral

PRACTICE – GET OUT YOUR MC CARDS! 3. You wear a silk shirt and go running. Which of the following will end up negatively charged? a) your skin b) the silk shirt 4. Your grandma cleans her kitchen glassware with a wool cloth. Which of the following will end up positively charged? a) the glassware b) the wool cloth

PRACTICE – GET OUT YOUR MC CARDS! Why do charged objects stay charged in dry weather? a) dry air acts as an insulator – it prevents the movement of electrons b) dry air acts as a conductor – it prevents the movement of electrons

PROBLEM SOLVE! – GET OUT YOUR MC CARDS! 6. The following observations are made of five objects A, B, C, D and E. A and B are rubbed together. A is lower on the ES series than B. B attracts both C and E. The force between C and D is repulsion. What are the possible charges on each object? a) A = (+), B = (-), C = (0), D = (+), E = (+) or (0) b) A = (-), B = (+), C = (0), D = (+), E = (+) or (0) c) A = (-), B = (+), C = (-), D = (-), E = (-) or (0) d) A = (-), B = (+), C = (-) or (0), D = (-), E = (-) or (0) A – B + C – or N D – E – or N