2Four Fundamental Forces GravityCosmic and MacroscaleElectromagneticMacroscale andMicroscaleWeakStrongSubatomicNuclear
3Electromagnetic Force Force of attraction or repulsion due to an imbalance of electric chargeOpposite Charges AttractLike Charges Repel
4Electric ChargeAtoms are composed of positive protons, neutral neutrons, and negative electronsNeutral atomshave equal numbers ofpositive protons and negative electrons
5Electric ChargeProtons and neutrons are locked in the nucleus and can not move freelyElectrons are found outside the nucleus in energy levels and are free to moveA positive or negative electric charge results from objects gaining or losing electrons
6Conservation of Charge When electrons are transferred from one object to another, no electrons are created or destroyed.The electrons removed from one object equals the electrons added to another object.
7Charging By Friction Results from rubbing objects together Called triboelectric chargingFriction strips electrons from atoms of one object and deposits them on another objectFriction transfers the electrons from the sweater to the balloonThe balloon and sweater have a balance of electric charge initiallyResulting in a slightly more positive sweater and a slightly more negative balloon
8Electron AffinityIn some materials, the electromagnetic force of attraction between the positive nucleus and the negative electrons is very strong. This attraction is called electron affinity.Electrons move from materials with low electron affinity to materials with high electron affinity.
9Conductors and Insulators Conductors are materials which allow electric charge to move through them easily.Insulators are materials which do not allow electric charge to move through them easily.Iron NailPlastic RodElectrons strongly bound to positive nucleusElectrons are loosely bound to positive nucleus
10Conduction Charging by contact Charging a neutral object by making contact with a charged objectThe resulting charge is always the same as the original charge.Requires a conductor
11ConductionWhen a negatively charged object touches a neutral object, the repulsive force between the electrons pushes the mobile electrons off of the negative object and onto the neutral object.Thus, the original negative charge is spread over both objects.Objects are separated after initial touch- Charged object touches neutral objectBoth objects have a negative chargeSome electrons move onto sphereNotice the negative charge on the original object is reduced becausesome electrons moved to the sphere
12ConductionWhen a positively charged object touches a neutral object, the force of attraction pulls mobile electrons off of the neutral object onto the positively charged objectResults in both objects obtaining a positive chargeObjects are separated after initial touch+ Charged object touches neutral objectSome electrons move to positive objectBoth objects have a positive chargeNotice the positive charge on the original object is reduced becausesome electrons moved onto the object from the sphere
13PolarizationA negatively charged balloon is brought near a neutral sphereThe negatively charges repel the electrons of the sphere pushing them to the opposite side of the sphere.Results in an object with two oppositely charged ends
14Van de Graaff Generator A motor at the base of the generator turns a large rubber belt which is stretched between two rollers located at each end of a long clear tube.Metal SphereRubber BeltMotor in Base
15Van de Graaff Generator As the rubber belt moves over the rollers, electrons are removed from the rollers and begin to build up on the belt.Wire brushes at the top of the clear tube remove the excess electrons from the belt and conduct the negative charge to the metal sphere at the top of the generator.
16Van de Graaff Generator The negative charge on metal sphere repels each other causing the charge to spread out evenly around the sphere.When the electromagnetic force of repulsion becomes too large, the negative charge “jumps” off the sphere to another object or the air.
17InductionCharging of a neutral object by bringing a charged object near (but not touching) it.Includes two processes: Polarization and GroundingResults in two oppositely charged objects
18InductionThe negative charged electrons on the sphere are removed by touching it with a finger (or other object)Grounding – connecting a charged object to Earth to allow electrons to travel to or from the object depending on the situation
19InductionThe finger (or grounding object) is removed and the balloon and sphere are separatedNotice the positive charge isequal to the negative chargeon the original balloon (thereIs no reduction of charge)