1. Dr. Jie ZouPHY 13711 Welcome to PHY 1371 General Physics III

2. Dr. Jie ZouPHY 13712 Chapter 16 Wave Motion

3. Dr. Jie ZouPHY 13713 Outline Introduction: What is a wave? Propagation of a disturbance (16.1) Elements for a mechanical wave Transverse and longitudinal waves Combination of transverse and longitudinal waves Pulse traveling on a string with speed v

4. Dr. Jie ZouPHY 13714 What is a wave? “…The essentially new thing here is that for the first time we consider the motion of something which is not matter, but energy propagated through matter.” - Einstein and Infeld, in The Evolution of Physics, 1961. Central feature of wave motion: Energy is transferred over a distance, but matter is not; the transfer of energy through space without the accompanying transfer of matter. All waves carry energy. Two main types of waves Mechanical waves: some physical medium is disturbed. Electromagnetic waves: they do not require a medium to propagate. Mechanical waves: The propagation of a disturbance through a medium.

5. Dr. Jie ZouPHY 13715 Propagation of a disturbance Elements for a mechanical wave: All mechanical waves require (1) some source of disturbance (2) a medium that can be disturbed (3) some physical connection through which adjacent portions of the medium can influence each other.

6. Dr. Jie ZouPHY 13716 Transverse and longitudinal waves Transverse wave: A traveling wave or pulse that causes the elements of the disturbed medium to move perpendicular to the direction of propagation. Longitudinal wave: A traveling wave or pulse that causes the elements of the medium to move parallel to the direction of propagation. Red arrow: direction of propagation. Blue arrow: Direction of particle displacement.

7. Dr. Jie ZouPHY 13717 Combination of transverse and longitudinal waves

8. Dr. Jie ZouPHY 13718 Quick Quiz 16.1 and 16.2 In a long line of people waiting to buy tickets, the first person leaves and a pulse of motion occurs as people step forward to fill the gap. As each person steps forward, the gap moves through the line. Is the propagation of this gap transverse or longitudinal? Consider the “wave” at a baseball game: people stand up and shout as the wave arrives at their location, and the resultant pulse moves around the stadium. Is this wave transverse or longitudinal?

9. Dr. Jie ZouPHY 13719 Pulse traveling on a string with speed v x axis: axis of the string; y axis: the transverse (vertical) displacement of the string (medium). Suppose that at t = 0, y(x, 0) = f(x). At some later time t: (1) Pulse traveling to the right: y(x,t) = f(x – vt) (2) Pulse traveling to the left: y(x,t) = f(x + vt) y(x,t) is called the wave function. The wave function y(x,t) represents the y coordinate of any element located at position x at any time t.

10. Dr. Jie ZouPHY 137110 Example 16.1 A wave pulse moving to the right along the x axis is represented by the wave function where x and y are measured in cm and t is in seconds. Plot the wave function at t = 0, t = 1.0 s, and t = 2.0 s. Find the speed of the wave pulse.

11. Dr. Jie ZouPHY 137111 Homework Ch. 16, P. 506, Problems: #2, 3. Note: these homework problems are from the 6 th edition of the textbook.