2ObjectivesExplain the similarities and differences between Newton’s law of universal gravitation and Coulomb’s law.Explain how force between two like charges and the force between two unlike charges are different.Describe how to create an electric field and interpret the information given in a drawing of an electric field.
3Universal Forces Include: gravitational and electrical Gravitational force acts between two or more massesElectrical force acts between two or more chargesCalled universal because each force behaves the same anywhere in the observable universe.The two forces are field forces and act over a distance (the masses or charges do not have to be touching – example – gravitational forces affect the earth and the moon or magnetic forces affecting two magnets).
4Gravitational Force Why cover gravitational force? 17th century, Isaac Newton.View video clip (control+click)Newton’s universal law of gravitationEvery object in the universe attracts every other object with a force that is directly proportional to the mass of each body and inversely proportional to the square of the distance between them.
5Formula for Gravitational Force G = universal gravitational constant = 6.67 x N•m2/kg2m1 = mass of first body in kilogramsm2 = mass of second body in kilogramsd = distance between the two bodies in metersFg = the gravitational force in Newtons
6Using the formula for gravitational forces Use the standard procedure of writing down the givens,solving for and formulas neededConvert masses to kilograms and distance to metersWrite down the formulaRearrange the formula if necessary to solve for needed componentIf you are solving for Fg and set up the problem correctly you will be able to m2 from the distance and kg2 from the masses and then cancel out the m2 and the kg2 with those in G (Nm2/kg2)so that your remaining unit is N (Newton) which is the correct unit of force.
7Notes on numbers with exponents: When you multiple number with exponents :1. multiply the numbers together as usualadd the exponents together– two positive exponents give you a larger positive exponent– two negative exponents give you a larger negative exponent- when exponents are of different signs you find the difference between them and give the sign of the larger exponent.When you have numbers with exponents in the numerator and denominatorDivide the numerator by the denominatorSubtract the exponent value in the denominator from the exponent value in the numerator
8Formula for FgIf you are solving for Fg and set up the problem correctly you will be able to calculate m2 from the distance and kg2 from the massescancel out the m2 and the kg2 with those in G (N·m2)kg2Your remaining unit is N (Newton) which is the correct unit of force.
10Set up the problem and solve Set up the problem and solve. Use our standard procedure and the notes from slides (I will check your work in class when I check your notes.)Check your answer by sliding the brown box away from example 1.11.
11Electric Charge Electrostatic forces, the comb and the CRT. Charge – property of and object that causes electrical force.Two types of charge: positive and negativeElectrical forces are either attractive or repulsive.Like charges repelOpposite charges attract.
13Origin of Charge Structure of atom. Charge of electron is equal in magnitude to proton but opposite in sign.Normal atom is neutral because number of protons and electrons are equal.
14Origin of Charge Charge can transferred Net Charge = #protons – #electronsCharge can transferredComb exampleBalloon example (in class)Principle of conservation of charge – net charge in an isolated system never changes.
15Electrical ForceIn 18th century, French scientist Charles Coulomb discovered the relationship between force, charge and distance.Coulomb’s lawThe electrical force between two charged bodies is directly proportional to the charge on each body and inversely proportional to the square of the distance between them.
16Electrical Force SI unit for charge is the Coulomb (C). Elementary charge of one electron or proton is x Cq1 and q2 are the charges on two objects.d = distance between charged objectsK = constant = 9.0 x 109 N•m2/C2
17Electrical ForceCoulomb’s law similar to Newton’s universal law of gravitation.But, gravitational force is always attractive.Direction for electrical force depends on charge of particles.
19Example 1.12 is on the next slide Set up the problem and solve. Use our standard procedure and the notes from slides (I will check your work in class when I check your notes.)Check your answer by sliding the brown box away from example 1.11.
21Scale and Universal Forces Small distance and mass as in atoms, electrical forces are important and gravitational force is insignificant.Large distance and mass, significance reverses.ThusElectrical forces govern the structure of atoms, molecules, solids, liquids and gases.Gravitational forces govern the structure of planets, stars, galaxies and the universe.
22Gravitational and Electrical Fields Field forces are alterations in space around the body creating the field.They are models used by scientists to help them understand and predict how forces are transmitted from one object to another.The field forces are vector quantities.
25Gravitational FieldElectrical FieldWhat happens when you substitute the respective laws into each equation above?E does not depend on size of test charge.g does not depend on size of test mass.
26Field Line DiagramsIllustration of a field can be done with field lines.Direction of field at any given point is tangent.Lines are close, field is strongLines are far apart, field is weak
27Forces, units and Formulas G = universal gravitational constant = 6.67 x N•m2/kg2m1 = mass of first body in kilogramsm2 = mass of second body in kilogramsd = distance between the two bodies in metersFg = the gravitational force in NewtonsGravitational forceGravitational FieldSI unit for charge is the Coulomb (C).Elementary charge of one electron or proton is x Cq1 and q2 are the charges on two objects.d = distance between charged objectsK = constant = 9.0 x 109 N•m2/C2Electrical forceElectrical Field