Changing objects

• Energy is the ability to do work
• 3 Ways to Charge Objects

  • Charging by friction
  • Charging by contact
  • Charging by induction
• Charging by Friction


  1. We rub 2 NEUTRAL objects together

  2. move from one object to the other
• If the objects are the same material, no charge is transferred
• Electrostatic series


  • Higher = loses e- (becomes +ve)
  • Lower = gains e- (becomes -ve)
• Electrostatic series


  • Hair = +ve
  • Comb = -ve
• When does your hair normally get staticky?

  In dry air (e.g., in the winter) OR in humid air (e.g., right after a shower)
• Dry air


  Insulator (not a conductor), and causes objects to become charged by static
• Humid air


  Has a lot more H2O molecules that pick up/"absorb" excess charge easily so static doesn't build up on objects (such as your hair)
• Discharging


  When excess charge is absorbed by H2O molecules in humid air
• Charging by Contact


  1. Charged object touches a NEUTRAL object

  2. move/spread out to balance the charges

  3. They move towards the object with the fewest e-

  4. Sometimes the e- "jump" the gap before full contact - this is an electric shock
• The neutral object gains the SAME CHARGE as the charged object that touched it
• If we touched a +ve object to a neutral object

  • Only ELECTRONS can move; p+ CANNOT be transferred
  • e- repel each other and want to spread out
  • They will move to the object with fewer e- (the +ve object)
• Charging by Induction


  1. Bringing a charged object NEAR but NOT TOUCHING a neutral object

  2. Only conductors can be charged by induction

  3. If the object is negatively charged, then the e- in the neutral object will be repelled (to the other side)

  4. If the object is positively charged, then the e- in the neutral object will be attracted (to the same side)

  5. The neutral object will have the OPPOSITE charge of the charged object (in one area)

  6. If we move the charged object away, the induced charge goes away (it's only TEMPORARY)

  7. We can make it permanent if the neutral object is grounded
• Grounding


  Connecting an object to the Earth, which is a giant supply of e- so they can go INTO the Earth or be sucked up FROM the Earth
• Electroscope


  • Device that allows you to test whether an object is charged
  • Main parts are a metal ball, metal rod, and metal leaves
  • When neutral, the leaves stay together
  • When positively or negatively charged, the leaves repel each other