Ch. 25 Vibrations and Waves

A vibration is a to and fro movement over a certain time period. (a pendulum) A wave is a to and fro motion in space and time.(ex. a stone dropped into a pond)

The period is the time it takes to make one complete vibration or cycle. (ex. The period of the earth is about days)

The properties of a wave are as follows: Crest Trough Amplitude Wavelength Frequency Wave speed

Wave frequency The hertz is the unit of frequency. Metric prefixes are often used to describe large frequencies such as those used in electronic devices. (ex. Megahertz(MHz) and kilohertz(kHz)

Wave speed Wave speed depends on what the wave is traveling through. Greater elasticity and greater density will increase wave speed. Sound travels about 330 to 350 m/s in air but about 4 times faster in water.

Wave equations V= f x w (Wave speed = wave frequency x wavelength) T=1/f (period = 1/frequency f=1/T (frequency = 1/period)

Types of waves Transverse – waves move perpendicular to source of vibration. (ex. Water waves, light waves, heat waves )

Types of waves Longitudinal – waves move parallel to the source of vibration. (ex. Sound waves)

Interference If two waves enter the same space at the same time they are said to interfere.

Constructive interference occurs when one part of a wave lines up with the same part of another wave.

Destructive interference occurs when one part of a wave reaches the same point as the opposite part of another wave. (ex. peak and trough)

Standing waves These occur when just the right vibration occurs and some parts of the wave remain stationary. These parts are called nodes.

Doppler effect This phenomena occurs when the source of the wave is moving with respect to the observer. The wave frequency appears to change as the wave source changes position.

Change in Pitch The most obvious example of this is when something moves toward us and then past us with its siren blaring. The pitch seems to drop as soon as it passes us.

Redshift and blueshift The doppler effect also occurs for light. When light is moving in the direction of the observer an increase in frequency known as a blue shift occurs.

Redshift and blueshift When light is moving away from an observer, a decrease in frequency known as a red shift occurs. Astronomers find this very useful in determining the relative speed of stars.

Bow waves These are v- shaped waves that occur when an object moves across a liquid surface at a speed that is greater than the actual speed of the wave.

Bow waves Because of the overlapping an amplification of the wave front occurs.

Sonic boom A sonic boom is simply a bow wave that occurs in air, which is 3-dimensional. These occur when an airplane surpasses the speed of sound or sound barrier.

Speed of sound The speed of sound is called Mach 1(about 750 mph). A sonic boom may reach you hours after a plane has actually broken the sound barrier. This is because sound travels at a limited speed.

Speed of light waves All forms of electromagnetic radiation travel at the same speed.(The speed of light). In a vacuum this value is 300,000,000 m/s or 186,000 miles/sec