General Physics 2: Newton's Laws of Motion

• General Physics 2 covers topics like Newton's Laws of Motion, Electric Charge, Electric Fields, and Electric Flux.

Newton's Laws of Motion

• 1st Law (Law of Inertia): An object remains at rest or in constant motion unless acted upon by an unbalanced force.
  • Inertia is an object's resistance to changes in its velocity.
  • Mass measures the amount of matter and is quantified in kilograms; more mass equates to more inertia.
• 2nd Law: Force equals mass times acceleration (F=ma).
• Unit of force is the Newton (N), where 1 N is the force needed to accelerate 1 kg by 1 m/s².
• Acceleration of Gravity (Earth) is 9.8 m/s².
• Weight (force) is calculated as mass times gravity.
• 3rd Law: Every action has an equal and opposite reaction.
• Objects on Earth are subject to friction, unlike objects in frictionless space.

Types of Friction:

• Sliding Friction: Occurs during ice skating
• Rolling Friction: Occurs during bowling
• Fluid Friction: Air or liquid resistance
• Static Friction: Initial friction when moving an object

Force

• Force is a push or pull that changes an object's motion.
• Different types of forces are:
  • Gravity: Force between objects
  • Static Electricity: Force of electrons
  • Magnetism: Force of a field
  • Friction: Opposing motion force
• Newton's 2nd Law shows different masses accelerate at the same rate on Earth due to differing forces.

Static Electricity

• Static electricity is built-up stationary electrical charge on a material's surface, resulting from an imbalance of electric charges.
• The word "electricity" comes from the Greek word "elektron", meaning amber, coined by William Gilbert.
• Objects typically have no net charge (neither negatively nor positively charged).
• A transfer of electrons is needed to build a charge.
• Removing electrons results in a positive charge.
• Adding electrons results in a negative charge.

Causes of Static Electricity

• Static electricity is caused by the transfer of electrons.
• A way of charging is through Friction, Conduction and Induction.
• Charging by Friction (Triboelectric Effect): Transferring electrons between objects when rubbed together.
• This tends to happen when both materials are electrically insulating and electrons cannot move freely.

Triboelectric Series

• Triboelectric Series is a list ranking materials by their tendency to gain or lose electrons (electronegativity).

History of Electricity

• Ancient Greeks (600 BC): Discovered amber rubbed with wool attracts objects (Thales of Miletus).
• 1700: Guillaume du Fay discovered two types of electricity: resinous (amber rubbed with wool) and vitreous (glass rubbed with silk).
• Electricity of the same kind repels, while opposite kinds attract.

Electric Charge

• There are two types of charge: positive (vitreous) and negative (resinous).
• Like charges repel; unlike charges attract.
• Charge can be transferred by rubbing objects, but the total charge remains constant.
• Matter comprises atoms containing three fundamental particles:
  • Electrons (negative): Coined by George Stoney, discovered by J.J. Thomson.
  • Protons (positive): Coined by Ernest Rutherford; discovered by Rutherford.
  • Neutrons (neutral): Coined and discovered by James Chadwick.
• Electrons carry a negative charge.
• Protons carry positive charge.
• Net Charge: Electrons > Protons = Negative. Electrons < Protons = Positive

Charge Quantization

• Net charge (Qnet) of an object is the whole number of electron units.
• Qnet = -eNe + eNp + 0Nn = e(Np – Ne) = ± ne.
• Law of Charge Conservation: The net amount of electric charge produced is zero, and "no net electric charge can be created nor destroyed."

Units of Charge:

• 1 electron = -1e
• The SI unit of charge is the Coulomb (C).
• Coulomb defined as the charge passing through the cross section of an electrical conductor carrying one ampere for one second.
• 1 Coulomb (C) = 6.241509074x1018 protons / 6.241x1018 protons.

Insulators and Conductors

• Materials are categorized by their treatment of charged particles.
  • Insulators: Hold charges in fixed positions; current does not flow; charges cannot re-arrange.
  • Conductors: Allow charges to move freely; current flows easily; charges may re-arrange.
• Semiconductors have conductivity between insulators and conductors.
• Insulators are charged by friction; gained electrons cannot escape.
• Conductors cannot be charged by friction; gained electrons escape easily.
• Charging by conduction: Transfer of electrons when objects touch. Charging by induction: Production of charge by proximity.

Coulomb's Law

• French physicist, Charles-Augustine de Coulomb, studied electric forces.
• A Torsion Balance is an instrument measuring electric forces magnitude.
• Coulomb noticed that the force doubled when charge on either sphere doubled and, force quadrupled if both charges doubled. Force decreased to one-fourth if the distance doubled.
• Coulomb's Law: Force on charged objects is proportional to the charge magnitudes' product, and inversely proportional to the distance squared.
• Law provides electric force that either object exerts, direction depends on the sign of each charge.
• If charges have the same sign the force is directed away (repel).
• If charges have opposite signs the force is directed toward (attract).

As an equation:

• F = k (Q1Q2/r2) (N). Where:
  • F is force (N)
  • k is constant (N• m²/c²)
  • Q1, Q2 are charges (C)
  • r is distance between charges (m)
• Constant k (Coulomb's law constant) is 8.988 x 10^9 N • m²/c².
• The value of k depends on the medium.
  • In air, k is 9.0 x 10^9 N • m²/C².
  • In water, k reduces by 80.
• Using permittivity of free space (ε0), Coulomb’s law is written as: F = (1/4πε0) * (Q1Q2/r2) (N).

Electric Field

• Michael Faraday used the idea of a field.
• Electric field extends outward from charge through space.
• Electric field is a vector field around a charged particle and electrical force per charge.
• Electric field is represented as N/C.
• A small positive test charge is used to investigate a field.
• defined as the force exerted on a test charge placed at that point divided by the magnitude of the test charge.
• Electric field due to a single point charge is: E = k(Q/r2)
• The total electric flux from enclosed space is defined as EA = Qenci
• The number of field lines is proportional to the charge magnitude.
• Field strength is proportional to the closeness of field lines.
• Positively charged particle electric field points radially away.
• Negatively charged particle electric field points radially toward.

Gauss's Law

• Gauss's law involves the concept of electric flux.
• Electric flux: The electric field passing through a given area.
• Gauss's law: total flux through a closed surface.
• Electric flux is defined as: ΦE = E • A (N • m²/C) where
  • ΦE is electric flux (N • m²/C)
  • E is electric field (N/C)
  • A is surface area (m²)

Electric Field Lines

• Drawn to indicate the direction of force due to field charge.
• Field lines begin on positive charges and end on negative charges.
• For isolated charges, field lines are at infinity.
• Line direction is tangent to field at any point.