Light

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 Description

Frequency The number of vibrations an object makes in a unit of time is an object’s frequency. The frequency specifies the number of back-and-forth vibrations in a given time (usually one second). Wave Description

Drop a wrench and a baseball bat on the floor, and you hear distinctly different sounds. Objects vibrate differently when they strike the floor. Natural frequency: the frequency at which an object vibrates when it is disturbed. Natural Frequency

Natural frequency depends on the elasticity and shape of the object. The natural frequency of the smaller bell is higher than that of the big bell, and it rings at a higher pitch. Natural Frequency

An un-mounted tuning fork makes a faint sound. Strike a tuning fork while holding its base on a tabletop, and the sound is relatively loud because the table is forced to vibrate. Its larger surface sets more air in motion. A forced vibration occurs when an object is made to vibrate by another vibrating object that is nearby. Forced Vibration

When the string is plucked, the washtub is set into forced vibration and serves as a sounding board. Forced Vibration

What do the following have in common?

Forced VibrationNatural FrequencyResonance += What do the following have in common?

If the frequency of a forced vibration matches an object’s natural frequency, resonance dramatically increases the amplitude. You pump a swing in rhythm with the swing’s natural frequency. Timing is more important than the force with which you pump. Even small pumps or pushes in rhythm with the natural frequency of the swinging motion produce large amplitudes. Resonance

If two tuning forks are adjusted to the same frequency, striking one fork sets the other fork into vibration. The pushes occur at the right time and are repeatedly in the same direction as the instantaneous motion of the fork. Resonance

A radio station sends out its broadcast over a particular frequency. (forced vibration) Your radio can tune to that frequency. (natural frequency) The sound is the resonance. Resonance

Resonance occurs whenever successive impulses are applied to a vibrating object in rhythm with its natural frequency. The Tacoma Narrows Bridge collapse was caused by resonance. Wind produced a force that resonated with the natural frequency of the bridge. Amplitude increased steadily over several hours until the bridge collapsed. Resonance

The effect of two or more wave interacting with each other. Interference

In constructive interference, the crest of one wave overlaps the crest of another and their individual effects add together. The result is a wave of increased amplitude, called reinforcement. In destructive interference, the crest of one wave overlaps the trough of another and their individual effects are reduced. The high part of one wave fills in the low part of another, called cancellation. Interference

a.In constructive interference, the waves reinforce each other to produce a wave of increased amplitude. b.In destructive interference, the waves cancel each other and no wave is produced. Interference

Both transverse and longitudinal waves display wave interference when they are superimposed. Interference

Have you ever noticed that as a sound approaches its pitch is higher, and as it moves away its pitch is lower?

The Doppler effect is the apparent change in frequency due to the motion of the source (or receiver). The greater the speed of the source, the greater will be the Doppler effect. The Doppler Effect

Sound The Doppler effect causes the changing pitch of a siren. When a firetruck approaches, the pitch sounds higher than normal because the sound wave crests arrive more frequently. When the firetruck passes and moves away, you hear a drop in pitch because the wave crests are arriving less frequently. The Doppler Effect

Light The Doppler effect also occurs for light. When a light source approaches, there is an increase in its measured frequency. When it recedes, there is a decrease in its frequency. The Doppler Effect

Increasing frequency is called a blue shift, because the increase is toward the high-frequency, or blue, end of the spectrum. Decreasing frequency is called a red shift, referring to the low-frequency, or red, end of the color spectrum. Distant galaxies show a red shift in their light. A measurement of this shift enables astronomers to calculate their speeds of recession. The Doppler Effect