2A wave is a disturbance that transfers energy from place to place. WavesWaves and EnergyA wave is a disturbance that transfers energy from place to place.In science, energy is defined as the ability to do work.To understand waves, think of a boat out on the ocean.If a wave disturbs the surface of the water, it will cause anything floating on the water to be disturbed, too.The energy carried by a wave can lift even a large ship as it passes.
3Many waves require something to travel through. Waves and EnergyMany waves require something to travel through.Water waves travel along the surface of the water, and sound waves travel through air.You can even make a wave travel along a rope.
4The material through which a wave travels is called a medium. WavesWaves and EnergyThe material through which a wave travels is called a medium.Gases (such as air), liquids (such as water), and solids (such as ropes) all act as mediums.Waves that require a medium through which to travel are called mechanical waves.
5WavesWaves and EnergyAlthough waves travel through a medium, they do not carry the medium itself with them.Look at the duck in the illustrations at the side.When a wave moves under the duck, the duck moves up and down.It does not move along the surface of the water.After the wave passes, the water and the duck return to where they started.
7WavesWaves and EnergyBreaking waves at a beach behave a little differently.When waves hit a beach, the water does move along with the wave.This happens because the ocean floor near the beach slopes upward.As the water at the bottom of the wave hits the slope, it moves up toward the top of the wave.The top of the wave gets bigger and continues to move forward.Eventually it topples over, turning white and frothy.
8Waves are created when a source of energy causes a medium to vibrate. What Causes Waves?Waves are created when a source of energy causes a medium to vibrate.A vibration is a repeated back-and-forth or up-and-down motion.This motion is the wave
9WavesWhat Causes Waves?A moving object has energy.The moving object can transfer energyto a nearby medium, creating a wave.For example, as the propellers of a motorboat turn, they disturb the calm water surface.The boat’s propeller transfers energy to the water.The propeller produces a wave that travels through the water.As the boat moves through the water, italso causes waves.
10Different types of waves travel through mediums in different ways. Waves are classified according to how they move.The three types of waves aretransverse waves, longitudinalwaves, and surface waves.
11The rope itself, however, moves up and down or from side to side. WavesTransverse WavesWhen you make a wave on a rope, the wave moves from one end of the rope to the other.The rope itself, however, moves up and down or from side to side.Waves that move the medium at right angles to the direction in which the waves are traveling are called transverse waves.
12Transverse means “across.” WavesTransverse WavesTransverse means “across.”As a transverse wave moves in one direction, the particles of the medium move across the direction of the wave.The diagram below showsthat some parts of therope are very high whilesome are very low.The highest parts of thewave are called crests,and the lowest parts arecalled troughs (trawfs).
13The photo below shows a different kind of wave. WavesLongitudinal WavesThe photo below shows a different kind of wave.If you stretch out a spring toy and push and pull one end, you can produce a longitudinal wave.Longitudinal waves (lawn juh too duh nul) move the particles of the medium parallel to the direction in which the waves are traveling.The coils in the springmove back and forthparallel to the wavemotion.
14WavesLongitudinal WavesNotice in that in some parts of the spring the coils are close together.In other parts, the coils are more spread out.The parts where thecoils are closetogether are calledcompressions(kum presh uns).coils are spread out, orrarefied, are calledRarefactions(rair uh fak shunz)
15WavesLongitudinal WavesAs compressions and rarefactions travel along the spring toy, each coil moves slightly forward and then back.The energy travels from one end of the spring to the other, creating a wave.After the wave passes, each part of the spring returns to the position where it started.
16Surface waves are combinations of transverse and longitudinal waves. These waves occur at the surface between two mediums, such as water and air.When a wave passes through water, the water (and anything on it) moves up and down, like a transverse wave on a rope.The water also moves back and forth slightly in the direction that the wave is traveling, like the coils of the spring.
17But unlike the coils of a spring, water does not compress. WavesSurface WavesBut unlike the coils of a spring, water does not compress.The up-and-down and back-and-forth movements combine to make each particle of water move in a circle.The diagram below shows the circular motion of surface waves.
18There are many different kinds of waves. Properties of WavesThere are many different kinds of waves.Waves can carry a little energy or a lot.They can be short or long.They can be rare or frequent.They can travel fast or slow.All waves, however, share certain properties.The basic properties of waves are amplitude, wavelength, frequency, and speed
19WavesProperties of WavesTo understand the properties of waves, it helps to represent a wave on a diagram.You can draw a transverse wave as shown in the diagram below.Think of the dashed line as the position of the rope before it is disturbed. This is its rest position. As the wave passes, the ropegoes above or belowthe rest position.Remember that the crestsand the troughs are thehighest and lowest pointson the wave.
20WavesProperties of WavesTo draw longitudinal waves, think of the compressions in the spring toy as being similar to the crests of a transverse wave.The rarefactions in the spring toy are like the troughs of a transverse wave.By treatingcompressions ascrests andrarefactions astroughs, you candraw longitudinalwaves in the same way as transverse waves.
21WavesProperties of WavesAmplitude is the maximum distance the particles of the medium carrying the wave move away from their rest positions.The amplitude is a measure of how much a particle in the medium moves when disturbed by the wave.The amplitude of awater wave is themaximum distance awater particle movesabove or below thesurface level of calmwater.
22WavesProperties of WavesWaves are produced by something vibrating.The farther something moves as it vibrates, the larger the amplitude of the resulting waves.You can increase the amplitude of the waves on a rope by moving your hand up and down a greater distance.This greater amount ofenergy is then transferredto the rope. Thus, theamplitude of a wave is adirect measure of itsenergy.
23WavesProperties of WavesCompare the two transverse waves in the diagram below. You can see that wave A goes up and down a greater distance than wave B.The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position.You can find the amplitude of a transverse wave by measuring the distance from the rest position to a crest or to a trough.
24WavesProperties of WavesThe amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.High-energy vibrations cause the compressions to be very crowded.This makes the rarefactions quite loose.Crowded compressions and uncrowded rarefactions are like high crests and low troughs.They mean that the longitudinal wave has a large amplitude.
26WavesProperties of WavesA wave travels a certain distance before it starts to repeat.The distance between two corresponding parts of a wave is its wavelength.You can find the wavelength of a transverse wave by measuring the distance from crest to crest or from trough to trough.You can find the wave-length of a longitudinalwave by measuring thedistance from onecompression to thenext.
27WavesProperties of WavesWave frequency is the number of complete waves that pass a given point in a certain amount of time.If you make waves on a rope so that one wave passes by every second, the frequency is 1 wave per second.Since waves are vibrations of a medium, frequency can also be described as the number of vibrations per second.
28Frequency is measured in units called hertz. WavesProperties of WavesFrequency is measured in units called hertz.A wave or vibration that occurs every second has a frequency of 1 Hz.If two waves pass you every second, then the frequency of the wave is 2 per second, or 2 hertz.The hertz was named after the German scientist Heinrich Hertz, who first produced radio waves in an experimental situation.
30WavesProperties of WavesThe speed, wavelength, and frequency of a wave are related to each other by a mathematical formula.If you know any two of the quantities in the speed formula—speed, wavelength, and frequency—you can calculate the third quantity.
31WavesProperties of WavesFor example, if you know the speed and the wavelength of a wave, you can calculate the frequency.If you know the speed and the frequency, you can calculate the wavelength.
32WavesProperties of WavesWaves in different mediums travel at different speeds.In a given medium and under the same conditions, the speed of a wave is constant.For example, all sound waves traveling through the air at the same pressure and at the same temperature travel at the same speed.If the temperature or pressure changes, the sound waves will travel at a different speed.