WAVES A way to transmit energy Waves are

WAVES: A way to transmit energy

Waves are defined as a periodic disturbance that carries energy from one place to another. A periodic disturbance is one that happens over and over again at regular intervals. . Like a bouncing ball, the motion repeats over and over again.

There are two kinds of waves you should recognize. Longitudinal or compression waves and transverse waves.

Longitudinal waves, like sound waves, are mechanical waves because they must have a material to travel through. The material they travel through is called the “medium”. The medium can be any material. Air Rock Water Wood Anything!

Sometimes longitudinal waves are referred to as compression waves because they are caused by a vibrating object compressing and rarefying the atoms or molecules of the medium. Vibrating object Alternating areas of compression and rarefaction in the medium.

• By vibrating back and forth, the vibrating object alternates between compressing and rarefying the molecules of the medium.

Areas of compression are high pressure areas where the molecules are squeezed closer together by a vibrating object. Areas of rarefaction are low pressure areas where the vibrating object pulls the molecules further apart.

In longitudinal waves the molecules of the medium vibrate along with the vibrating object. Molecules of the medium vibrate back and forth on each side of a fixed resting point, transferring their kinetic energy to adjacent molecules. In this way the energy is transferred, but the molecules remain in place.

Longitudinal waves get their name because the vibration that puts energy into the wave vibrates in the same plane in which the energy moves.

Transverse Waves In a transverse wave the particle displacement is perpendicular to the direction of the energy transfer. The particles do not move along with the wave, they simply vibrate up and down about their individual rest positions as the wave passes by. Pick a single particle and watch its motion.

The wavelength of a wave is the distance between successive vibrations. Wavelength is measured in meters. Here is how wavelength is measured on a transverse wave.

This diagram shows how wavelength can be measured on a longitudinal wave. It is measured from compression to compression.

The Amplitude of a wave determines how much energy a wave is carrying. This can easily be seen in a transverse wave where the wave height is the amplitude. Obviously, the higher the wave crest the higher the amplitude, and the greater the wave energy.

In longitudinal waves amplitude is a measure of the degree of compression. The more compressed the compressions are the greater the amplitude. Low amplitude ( Less compression) High amplitude ( greater compression)

Wave velocity is a measure of how fast the energy is being transferred. Wave velocity is measured in meters per second (m/s).

Wave frequency, for a transverse wave, is a measure of how many wave crests pass a point in one second. Wave frequency is measured in Hertz. 1 Hertz is equal to 1 wave per second. If 5 waves pass the smiley in one second, then the wave frequency is 5 Hz or 5 waves per second. Longitudinal wave frequency is how many compressions pass a point in one second.

Wave period, for transverse and longitudinal waves, is the time it takes for one complete wave ( one wavelength) to pass a point. If it takes. 3 seconds for a single wave to pass the smiley then the wave period is. 3 s. Wave period is measured in seconds.

The relationship between wave frequency, wave length, and wave velocity is expressed in a very simple equation, V=f λ. In this equation V is velocity measured in m/s, f is frequency measured in Hz, and λ is wavelength, measured in meters. λ is the Greek letter Lambda. Shown below is an example problem using this equation. EXAMPLE 1: What is the velocity of a longitudinal wave with a frequency of 2000 Hz and a wavelength of. 17 m? Solution

Three ways to use the wave equation.

Two More Equations Wave period is measured in seconds per wave. Wave frequency is measured in waves per second… Hmmm… they look like they are the inverse of each other! What is the frequency of a wave with a period of. 17 s Just find the inverse of. 17 s The answer is 5. 9 Hz

What is the Period of a wave with a frequency of. 046 Hz? Just find the inverse of. 046 Hz The answer is 21. 7 s

THE DOPPLER EFFECT: an apparent change in frequency caused by the motion of the wave source The source of a wave can be stationary, such as a bell, a light bulb, or even a ripple spreading outward in a pond of water, or it can be moving. When the source of a wave is moving the waves are compressed closer together in the direction of motion and spread further apart behind the source. This changes the frequency of the wave. Stationary source Moving source

THE DOPPLER EFFECT AS IT APPLIES TO SOUND WAVES Joe hears a low frequency Moe hears a higher frequency

Here is a situation in which you will recognize the Doppler effect. The the driver of a car keeps a hand on the horn constantly as he approaches and then passes an observer. Listen to the high pitch as the car approaches and the low pitch after the car passes the observer. DOPPLER EFFECT

THE DOPPLER EFFECT AS IT APPLIES TO LIGHT WAVES Low frequency long wavelength end of the spectrum An observer on the Earth sees light shifted towards the red ( lower frequency) end of the spectrum. This is referred to as the RED SHIFT.

To be continued…