Nature of Waves

Objectives:

1.    Explain what a wave is in terms of energy.

2.    Recognize and classify waves as transverse of longitudinal given a few examples of waves.

3.    List two properties of a medium that affect the speed of a wave.

4.    Identify the crest and trough of a wave.

5.    Be able to distinguish between the compression and the rarefaction of a longitudinal wave.

Resources:

Notes:

Vibrations, Waves and Energy:

A vibration is a back and forth disturbance in a medium.  A wave is a vibration that transfers energy through matter or space.    Examples of common waves that we come in contact with are sound and light.  No matter whether you are talking about vibrations or waves, all of them can be characterized by the following four characteristics: amplitude, wavelength, frequency, and speed.

Characteristics of Waves:

Amplitude

The amplitude of a wave can be described as the maximum distance the molecules are displaced from their starting place .

• Is the measure of the intensity of a wave
• As energy increases, amplitude increases

(by Cattell and J. Dombeck (Univ of Minnesota) and M. Temerin and F. S. Mozer (Univ of Ca, Berkeley)

Wavelength

The wavelength of a wave can be described as the distance between 2 consecutive crests or troughs

• The crest refers to the highest point of a wave

• The troughs refer to the lowest points of a wave

• The shape of a the wave forms a sine curve and describes simple harmonic motion (the motion that a pendulum makes).

(imagers.gsfc.nasa.gov)

Frequency

The frequency is a measure of the amount of crests or troughs that pass through a point per unit time.  The amount of time a single wave takes to complete its cycle is called the period of the wave.  The frequency of the wave is inversely related to the period of the wave.  (frequency =  1/period)

• The number of cycles per unit time

• Transverse – crests or troughs/second

• Compression – compressions or rarefactions/second

• Unit is the hertz (Hz)         1Hz = 1wave/second

(www.lbl.gov/images)

Period

• period is the amount of time it takes for one complete wave to pass a fixed point

• period = 1/frequency

• period = wavelength/speed