# Mechanics Lecture Videos Fall 2019

Videos of lectures on mechanics by Dr. Ruth Chabay, Fall 2019. These include instruction on the use of VPython to model physical systems.
Lecture 1: Vectors.
Lecture 2: Velocity; computation using VPython; momentum.
Lecture 3: Interactions; relativistic momentum; momentum change; the Momentum Principle.
Lecture 4: Using the Momentum Principle to predict the future; analytical solution for constant force.
Lecture 5: How to take notes; the spring force; the gravitational force.
Lecture 6: Details of the gravitational force.
Lecture 7: Review of the meaning of the program statement “p = p + Fnet*deltat”; the charges of various elementary particles; the electric force; conservation of momentum.
Lecture 8: Review the relative strengths of electric and gravitational forces; contact forces; atomic nature of matter and the ball-and-spring model; the size of an atom; the stiffness of series and parallel springs.
Lecture 9: The stiffness of a metal wire in terms of the stiffness of the interatomic spring-like electric force; the speed of sound in a solid; Young’s modulus; friction; normal force; coefficients of static and kinetic friction. (At 53:25 the axes of the stress-strain curve are accidentally labeled incorrectly; the horizontal axis should be stress and the vertical axis should be strain; when the stress becomes bigger than the “yield” stress, the strain grows very rapidly.)
Lecture 10: Comments on the first test; determining forces from observing motion; freebody diagrams; statics and dynamics; perpendicular and parallel components of force; vector dot product.
Lecture 11: More on parallel and perpendicular components of forces and their effects on motion; the kissing circle; the important special case of circular motion at constant speed; circular gravitational orbits.
Lecture 12: Harmonic oscillator; the Energy Principle; total, rest, and kinetic energy of a particle; mechanical work.
Lecture 13: Changes in rest energy; neutron decay; potential energy.
Lecture 14: The relation of mgy to 1/r; electric potential energy; graphs of energy; the importance of choosing initial and final states for applying the Energy Principle; ionization energy of a hydrogen atom; general properties of potential energy; a nuclear fusion reaction. Here are two videos from 2010 that go further on the topic of energy: the mass of an oxygen molecule and more on nuclear reactions.
Lecture 15: Spring potential energy; applying the Energy Principle; the importance of being explicit about the choice of system.
Lecture 16: Review of types of potential energy; internal energy; chemical energy; thermal energy; thermometers; W and Q; specific heat; thermal equilibrium; the energetics of a horse running up a hill.
Lecture 17: Center of mass; translational kinetic energy; kinetic energy relative to the center of mass; moment of inertia; moment of inertia as an integral.
Lecture 18: Review of what is meant by “collision”; elastic vs. nonelastic collisions; two-cart elastic collision; two-cart sticking collision; in response to student questions, some comments about quantized energy and m = E/c2; collisions of a ping-pong ball and a bowling ball; change of reference frame.
Lecture 19: The Angular Momentum Principle; the right-hand rule; the vector cross product; translational angular momentum and rotational angular momentum (L = Iω).
Lecture 20: Revew of angular momentum; torque and angular momentum; a child runs and jumps onto a merry-go-round with analysis that uses all three mechanics fundamental principles — the Momentum Principle, the Energy Principle, and the Angular Momentum Principle.
Lecture 21: Energy quantization; photon absorption and emission; the Bohr model for the hydrogen atom; quantized spring-mass systems. The values for h and h-bar are reversed on the blackboard.
Lecture 22: Entropy; some phenomena do not violate the Energy Principle yet essentially never happen; diffusion of lattice gas; the Einstein model of a solid; counting microstates; a VPython program that computes the probability of the distribution of energy between two blocks; definition of entropy.
Lecture 23: Entropy and temperature; graphs of the distribution of microstates; the 2nd Law of Thermodynamics; thermal equilibrium of two blocks; dS/dE = 1/T; melting of ice; freezing of water; heat capacity.
Lecture 24: Review of angular momentum; point particle and extended systems.The Two Pucks Demo video is available here. A video from 2010 goes more deeply into point particle and extended systems.
Lecture 25: Review of Chapter 12; number of ways to arrange energy; entropy; temperature; heat capacity; review of curving motion.