12-3: Properties of Waves Objectives: Distinguish local particle vibrations from overall wave motion. Differentiate between pulse waves and periodic waves. Interpret wave forms of transverse and longitudinal waves. Apply the relationship among wave speed, frequency, and wavelength to solve problems. Relate energy and amplitude.

Wave Motion If you see a drop of water on a smooth surface of water you will notice the waves. The water will move locally, but does not move out in the same manner the wave does. Consider a leaf floating in the water, it moves up and down over the waves. The water moves in the same way. The disturbance moves, not the medium

Wave Motion Ripple waves start with a disturbance which moves the water around it, which in turn moves the water continually moving outward in a circle. In this example, the water in the pond is the medium through which the disturbance travels. Particles in the medium—in this case, water molecules— vibrate up and down as waves pass. Note that the medium does not actually travel with the waves. After the waves have passed, the water returns to its original position.

Wave Motion In order for sound waves to travel, they must have a medium such as air or water. Waves that require a material medium are called mechanical waves. – Water waves, sound waves, etc… In following chapters we will study waves that do not require a medium. – visible light, radio waves, microwaves, and X rays

Wave Types One of the simplest ways to demonstrate wave motion is to flip one end of a taut rope whose opposite end is fixed. The flip of your wrist creates a pulse that travels to the fixed end with a definite speed. A wave that consists of a single traveling pulse is called a pulse wave. Now imagine that you continue to generate pulses at one end of the rope. Together, these pulses form what is called a periodic wave. – Whenever the source of a wave’s motion is a periodic motion, such as the motion of your hand moving up and down repeatedly or a pendulum, a periodic wave is produced.

Sine waves will describe simple harmonic motion A wave whose source vibrates with simple harmonic motion is called a sine wave.

Frank Oppenheimer demonstrates that a pendulum swinging back and forth traces out a straight line over a stationary surface, and a sine curve when the surface moves at constant speed.

A weight attached to a spring undergoes simple harmonic motion. A marking pen attached to the bob traces a sine curve on a sheet of paper that is moving horizontally at constant speed. A sine curve is a pictorial representation of a wave.

Transverse Waves Suppose you create a wave along a rope by shaking the free end up and down. The motion of the rope is at right angles to the direction in which the wave is moving. Whenever the motion of the medium is at right angles to the direction in which a wave travels, the wave is a transverse wave.

The high points on a wave are called crests. The low points on a wave are called troughs. The term amplitude refers to the distance from the midpoint to the crest (or trough) of the wave. The amplitude is the maximum displacement from equilibrium. Wave Length- the distance between two adjacent similar points of the wave, such as from crest to crest or from trough to trough. (Lambda λ) Parts of the transverse wave

Sometimes the particles of the medium move back and forth in the same direction in which the wave travels. When the particles oscillate parallel to or along the direction of the wave, the wave is a longitudinal wave. Longitudinal Waves What type of wave is a? b?

Longitudinal Waves

Period, Frequency, and Wave Speed The period of a wave is inversely related to its frequency. speed of a wave = frequency × wavelength v=fλ The speed of a mechanical wave is constant for any given medium. – Speed of light: 300 million meters per second – Speed of sound: 343 meters per second – It takes light approximately 1.2 seconds to reach the moon. How long does it take sound? When a mechanical wave’s frequency is increased, its wavelength must decrease in order for its speed to remain constant. – The speed of a wave changes only when the wave moves from one medium to another

The piano string tuned to middle C vibrates with a frequency of 264 Hz. Assuming the speed of sound in air is 343 m/s, find the wavelength of the sound waves produced by the string. v=343m/s, f =264Hz, λ=? *v=fλ λ=v/f

Assignment P. 458 – Questions 1-3 and 5