Hnrs Physics Final Review Summary Wrk Dne By A Cnstant Frce: Wrk describes a frce s tendency t change the speed f an bject. Wrk is dne nly when an bject mves in respnse t a frce, and a cmpnent f the frce pints in the directin f the mtin. W = F Δx cs θ Wrk Dne By A Variable Frce: When the frces changes as the bject mves, the wrk dne by the frce is fund by calculating the area under a frce vs. psitin graph. W = Area Wrk-Energy Therem: The Wrk-Energy Therem says: W = ΔKE Where W is the ttal wrk dne by all frces. Cnservatives frces cnserve energy when they d wrk n a system. Nn-cnservative frces change the ttal energy when they d wrk n a system. The change in energy caused by wrk dne by a nn-cnservative frce is given by: W n.c = ΔE
Energy: In the absence f nn-cnservative frces, r when nn-cnservatives frces d n wrk n an bject, energy is cnserved. The types f energy we studied this year are: KE = 1 2 m v2 (Kinetic Energy) PE g = m g h (Gravitatinal Ptential Energy) PE s = 1 2 k (Δx)2 (Spring Ptential Energy) Pwer: Pwer describes the rate at which wrk is being dne. There are several frmulas fr calculating pwer, including: P = W Δt P = F v P = ΔE Δt (Fr nn-cnservative) Definitin f Impulse: J avg F avg Δt Where F avg is the average frce exerted ver sme time Δt. Impulse-Mmentum Therem: J = Δp (Impulse-Mmentum Therem) Remember that mmentum is a vectr F thrust = v ( dm dt ) Cnservatin f Mmentum & Cllisins: p f = p 0 (Cnservatin f Mmentum) Cnservatin f mmentum applies: During all types f cllisins When there is n external impulse
Cllisins: Elastic Cllisin - Energy and mmentum are cnserved Inelastic Cllisin Mmentum is cnserved, Energy is nt cnserved Perfectly Inelastic Cllisin Objects stick t tgether after the cllisin. Mmentum is cnserved, Energy is nt cnserved. Elastic Cllisins: Variables: 2 Initial velcities 2 Final velcities Equatins: Cnservatin f Mmentum Cnservatin f Energy Perfectly Inelastic Cllisins: Center f Mass: Variables: 2 Initial velcities 1 Final velcities Equatins: Cnservatin f Mmentum x c.m. = x i m i m i x c.m. = x λ(x)dx λ(x) dx Learning Objectives: Calculate the center f mass fr a set f discrete masses Calculate the center f mass fr a cntinuus bject with a mass distributin Electrstatic Frce: Between pint charges: F C = k q 1 q 2 r2 (Culmb s Law) Attractive fr ppsite charges, repulsive fr like charges Caused by an electric field: F E = q E
Electric Fields: The electric field generated by a pint charge E = k q r2 (fr pint charges) Rules fr drawing electric field lines: 1. Pint away frm psitive charges, twards negative charges 2. Lines start and end n either a charge r at an infinite distance away 3. Electric field lines never crss Electrstatic Energy: Between pint charges: PE E = k q 1 q 2 r Electrstatic Ptential (Vltage): Created by a pint charge: V = k q r Relatinship t Energy: ΔPE = q ΔV Equiptential lines always pint perpendicular t the electric field lines Electrstatics & Cnductrs: Inside a cnductr: E = 0 N C V = cnstant Current: Defined as: I = Δq Δt
Resistrs: Resistance f a wire: ρ L R = A Where ρ is the resistivity f the wire, L is its length, and A is its crss-sectinal area Ohm s Law: ΔV = I R Pwer lst inside a resistr: P = I V = I 2 R = V2 R Equivalent Resistance: R eq = R 1 + R 2 + (fr resistrs in series) 1 R eq = 1 R 1 + 1 R 2 + (fr resistrs in parallel) Parallel Series Circuits: Kirchff s Laws: Vltage drp arund any clsed lp in a circuit is always 0 V. Current flwing int a junctin must equal the current flwing ut f the junctin Measurements: An ammeter is used t measure current The ammeter has very little resistance The ammeter must be cnnected in series with the circuit A vltmeter is used t measure the vltage drp acrss a circuit The vltmeter must be cnnected in parallel with the circuit The vltmeter has a very large resistance