* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Physics 7B - AB Lecture 3 April 24 Vectors
Fictitious force wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Specific impulse wikipedia , lookup
Quantum vacuum thruster wikipedia , lookup
Faster-than-light wikipedia , lookup
Classical mechanics wikipedia , lookup
Equations of motion wikipedia , lookup
Derivations of the Lorentz transformations wikipedia , lookup
Matter wave wikipedia , lookup
Velocity-addition formula wikipedia , lookup
Bra–ket notation wikipedia , lookup
Symmetry in quantum mechanics wikipedia , lookup
Angular momentum wikipedia , lookup
Variable speed of light wikipedia , lookup
Tensor operator wikipedia , lookup
Work (physics) wikipedia , lookup
Special relativity wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Relativistic mechanics wikipedia , lookup
Four-vector wikipedia , lookup
Angular momentum operator wikipedia , lookup
Photon polarization wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Classical central-force problem wikipedia , lookup
Centripetal force wikipedia , lookup
Newton's laws of motion wikipedia , lookup
Physics 7B - AB Lecture 4 April 24 Chapter 6 Galilean Space-Time Model, lots of Vectors, Intro. to Force, Momentum Lecture slides available at http://physics.ucdavis.edu/physics7 1 Course Website http://physics.ucdavis.edu/physics7 Click on Physics 7B-A/B Today Quiz 2! May is a busy month. There will be four Quizzes. 2 What is Galilean Space-Time model about? The Galilean Space-Time Model In our ordinary experience, three spatial dimensions and one time dimensions are all independent of each other. z Ex. You walk on a moving bus, y what is your V ? w.r.t.the ground x What if the bus was moving really fast? Like close to the speed of light? (i.e., C = 3 x 108 m/s) 3 What is Galilean Space-Time model about? The Galilean Space-Time Model In our ordinary experience, three spatial dimensions and one time dimensions are all independent of each other. z Ex. You walk on a moving bus, y what is your V ? w.r.t.the ground x If the speed of the bus was close to the speed of light… The Special Relativity Model of Space-Time The three spatial dimensions are NOT independent of time. i.e. Someone on the moving bus and someone on the ground will measure different velocity. 4 Models in 7B are based on Galilean SpaceTime model. Good news is, The predictions of special relativity agree well with Galilean SpaceTime model in their common realm of applicability, specifically in experiments in which all velocities are small compared to the speed of light. z y x What are the forces exerted on the airplane for it to accelerate? Why does she start spinning much faster when she pulls her arms and legs in?5 To describe the motion of objects, we use several vector quantities such as… • Position vector R e.g. Rinitial, Rfinal • Displacement vector ∆R = Rfinal – Rinitial • Velocity vector v = dr/dt • Acceleration vector a = dv/dt • Force vector F •Linear momentum vector p = mv New physical quantities! • Angular momentum vector L = rptangential Ok… What were vectors again?? 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 Example #1 I take four steps right and three steps up, what is my displacement? 19 Example #2 If I take a different path from point A to point B, would my displacement be different as well? B ∆RAB A completely different path A 20 vave = ∆R/ ∆t, v = dR/ dt Therefore, velocity (vector) points in the same direction as the displacement (vector) The magnitude of velocity is a positive number called speed 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 36 36 37 37 38 38 39 39 40 40 Introduction to Conservation of Momentum Momentum is another (vector) quantity Nature chooses to conserve (for a closed system). 41 Momentum For a particle: Defined by p = mv Is a vector, points in the same direction as v (see above equation) For a system: Defined by adding together the momentum vectors of everything that makes up the system, I.e. ptotal = ∑pi = p1+ p2+ p3+… Is conserved for a system if nothing external pushes or pulls on it Has units of kg m/s 42 Conservation of Momentum Example Rifle recoil Before shooting (at rest) 43 Conservation of Momentum Example Rifle recoil Before shooting (at rest) vbullet After shooting pbullet 44 Conservation of Momentum Example Rifle recoil Before shooting (at rest) vbullet pbullet After shooting vRifle pRifle 45 Conservation of Momentum Railroad cars collide A 10,000kg railroad car A, traveling at a speed of 24m/s strikes an identical car B, at rest. If the car lock together as a result of the collision, what is their common speed afterward? vAi i =0 v B Before collision After collision A B pAi A+B At rest vA+Bf 46 Conservation of Momentum Railroad cars collide A 10,000kg railroad car A, traveling at a speed of 24m/s strikes an identical car B, at rest. If the car lock together as a result of the collision, what is their common speed afterward? vAi i =0 v B Before collision After collision A B pAi A+B At rest vA+Bf pA+Bf 47 • • When does momentum of something change?? … when a force F acts on the something during a time interval e.g. A bat hits a baseball change in momentum is called: Impulse Impulse Is related to the net external force in the following way: Net Impulseext = ∆ p = ∫ ∑ Fext(t)dt Approximate a varying force as an average force acting during a time interval ∆t Net Impulseext = ∆ p = ∑ Fave.ext x ∆ t 48 DLM8&9 : Use of vectors, Force Model, Some new ideas: Force diagram, Momentum chart Next week May1 Quiz3(20min) will cover: Today’s lecture (exclude momentum, force, Impulse) Activities and FNTs from DLM7 and Activities from DLM8 Bring Calculator! Closed-book, formulas will be provided. 49 Be sure to write your name, ID number & DL section!!!!! 1 MR 10:30-12:50 Dan Phillips 2 TR 2:10-4:30 Abby Shockley 3 TR 4:40-7:00 John Mahoney 4 TR 7:10-9:30 Ryan James 5 TF 8:00-10:20 Ryan James 6 TF 10:30-12:50 John Mahoney 7 W 10:30-12:50 Brandon Bozek 7 F 2:10-4:30 Brandon Bozek 8 MW 8:00-10:20 Brandon Bozek 9 MW 2:10-4:30 Chris Miller 10 MW 4:40-7:00 Marshall Van Zijll 11 MW 7:10-9:30 Marshall Van Zijll 50