PHYS16 – Lecture 4 Motion Ch. 2 Motion in 1D Looney Tunes

Before we begin… this class is different My role vs. your role – My role… Guide, Resource, Demonstrator – Your role… Thinker, Inquisitor, Observer The role of homework – Physics is about trying to describe our world with a set of mathematical equations – Homework is not regurgitating information Cracking the problem – which eqs./concepts to use Solving the problem – apply the math correctly

Ch. 2 Motion in 1D – Position, Velocity, and Acceleration – Free Fall Ch. 4 Motion in 2D – Projectile Motion – Relative Motion Motion

Intro – Motion pre-question If a 0.50 kg ball is launched straight up and is given an initial velocity of 15 m/s, what will be the velocity of the ball on the way back down at the launch point? (Note: assume air resistance is negligible and that g=9.8 m/s 2.) A) It is the same as when it was launched. B) It is dependent on initial velocity. C) It is dependent on the acceleration constant. D) It is dependent on the angle it was shot at. E) None of the above

Displacement, Velocity, Acceleration

Displacement Displacement vs. Distance – Displacement = change in position – Distance = total position traversed

Velocity Velocity vs. Speed – Avg. Velocity – – Avg. Speed – – Inst. Velocity – – Inst. Speed – Can the magnitude of average velocity ever equal the average speed?

Acceleration – Avg. Acceleration – – Inst. Acceleration – com Position graph where acceleration is not 0

Displacement, Velocity, Acceleration XVaXVa

Demo: Remote Control Car

Questions Can displacement be zero and distance be positive? Can distance ever be negative? Can speed ever be negative? Can acceleration be negative? Can an object that is stopped at t=0 have a positive acceleration? If an object is traveling at a constant velocity can it have an acceleration? Yes No Yes No

Free Fall

Object under influence of the Earth’s gravity is in free fall Dropped, thrown up, thrown down -> acceleration due to gravity is the same g=9.80 m/s 2, a y =-g

Derive Kinematic Equations

Conclusions Displacement and Distance are different! Avg. Speed is NOT the magnitude of Avg. Vel. Displacement -> Velocity -> Acceleration (take derivatives) Const. acceleration gives the three equations