WAVES ARE EVERYWHERE?

NATURE OF WAVE

WHAT IS A WAVE?•Waves are an energy transport phenomenon, a way to transport energy from one location to another.

•Waves are a disturbance that travels through a medium from one location to another; a wiggle in space and time.

WHAT MAKES A WAVE A WAVE?

•Waves are caused by vibrations

•A vibration (or oscillation) is a back-and-forth or up-and-down motion; a wiggle in time.

•A wave does NOT carry matter with it! It just moves the matter as it goes through it.

WHAT IS A MEDIUM?•A medium is a substance or material that carries the wave.

• • •The wave medium is not the wave and it doesn't make the wave; it merely carries or transports the wave from its source to other locations.

TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.

TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.

CHECK YOUR UNDERSTANDING

ANSWER

•False.•A sound wave involves the movement of energy from one location to another, not the movement of material. The air molecules are the particles of the medium, and they are only temporarily displaced, always returning to their original position.

CHECK YOUR UNDERSTANDING

•Mac and Tosh are experimenting with pulses on a rope. They vibrate an end up and down to create the pulse and observe it moving from end to end. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?

ANSWER

•The point returns to its original position. Waves (and pulses) do not permanently displace particles from their rest position.

CHECK YOUR UNDERSTANDING

A medium is able to transport a wave from one location to another because the particles of the medium are ____.a. frictionless b. isolated from one anotherc. able to interactd. very light

ANSWER

• Answer: C• For a wave to be transmitted through a medium, the individual particles of the medium must be able to interact so that they can exert a push and/or pull on each other; this is the mechanism by which disturbances are transmitted through a medium.

CHECK YOUR UNDERSTANDING

• Minute after minute, hour after hour, day after day, ocean waves continue to splash onto the shore. Explain why the beach is not completely submerged and why the middle of the ocean has not yet been depleted of its water supply.

•Ocean waves do not transport water. An ocean wave could not bring a single drop of water from the middle of the ocean to shore. Ocean waves can only bring energy to the shore; the particles of the medium (water) simply oscillate about their fixed position. As such, water does not pile up on the beach.

ANSWER

CATEGORIES OF WAVES•MECHANICAL

WAVE-- is a wave that is an oscillation of matter, and therefore transfers energy through a medium

• Some of the most common examples of mechanical waves are water waves, sound waves, and seismic waves.

ELECTROMAGNETIC WAVES

• – DO NOT NEED matter (or medium) to transfer energy

• They do not need a medium, but they can go through matter (medium), such as air, water, and glass.

• EXAMPLES are: Radio waves, Light waves, thermal radiation, X ray, visible light, microwave, infrared, gamma rays etc. are the example of electromagnetic waves. These waves together form the electromagnetic spectrum.

CATEGORIES OF A WAVES•Transverse waves: Waves in which the medium moves at right angles to the direction of the wave.

Transverse waves are always characterized by particle motion being perpendicular to wave motion.

PARTS OF TRANSVERSE WAVES:

Crest: the highest point of the wave

Trough: the lowest point of the wave

PARTS OF TRANSVERSE WAVES:

•The wavelength is the horizontal distance, either between the crests or troughs of two consecutive waves.

PARTS OF TRANSVERSE WAVES:

•The amplitude is the peak (greatest) value (either positive or negative) of a wave. The distance from the undisturbed level to the trough or crest.

AN OCEAN WAVE IS AN EXAMPLE OF A MECHANICAL TRANSVERSE WAVE

COMPRESSIONAL (OR LONGITUDINAL) WAVES:•Waves in which

the medium moves back and forth in the same direction as the wave.

PARTS OF LONGITUDINAL WAVES:

Compression: where the particles are close together

Rarefaction: where the particles are spread apart

PARTS OF LONGITUDINAL WAVES:

The wavelength is the distance from compression to compression or rarefaction to rarefaction in a compressional wave.

A transverse wave is transporting energy from east to west. The particles of the medium will move_____.a. east to west only b. both eastward and westwardc. north to south onlyd. both northward and southward

CHECK YOUR UNDERSTANDING

ANSWER•Answer: D•The particles would be moving back and forth in a direction perpendicular to energy transport. The waves are moving westward, so the particles move northward and southward.

•A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction. This type of wave is known as a ____.

a. mechanical b. electromagneticc. transverse d. longitudinal

CHECK YOUR UNDERSTANDING

•Answer: D•The particles are moving parallel to the direction that the wave is moving. This must be a longitudinal wave.

A sound wave is a mechanical wave, not an electromagnetic wave. This means that______.a. particles of the medium move perpendicular to the direction of energy transport. b. a sound wave transports its energy through a vacuum.c. particles of the medium regularly and repeatedly oscillate about their rest position.d. a medium is required in order for sound waves to transport energy.

•Answer: D•Mechanical waves require a medium in order to transport energy. Sound, like any mechanical wave, cannot travel through a vacuum.

Which of the following is not a characteristic of mechanical waves?

a. They consist of disturbances or oscillations of a medium. b. They transport energy.c. They travel in a direction that is at right angles to the direction of the particles of the medium.d. They are created by a vibrating source.

•Answer: C•The characteristic described in statement c is a property of all transverse waves, but not necessarily of all mechanical waves. A mechanical wave can also be longitudinal.

•8. The sonar device on a fishing boat uses underwater sound to locate fish. Would you expect sonar to be a longitudinal or a transverse wave?

•Answer: Longitudinal•Only longitudinal waves are capable of traveling through fluids such as water. When a transverse wave tries to propagate through water, the particles of the medium slip past each other and so prevent the movement of the wave.

WATER WAVES

RAYLEIGH SURFACE WAVES

ANATOMY OF A WAVE

•The crest of a wave is the point on the medium that exhibits the maximum amount of positive or upward displacement from the rest position.

•The trough of a wave is the point on the medium that exhibits the maximum amount of negative or downward displacement from the rest position.

•The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position.

•The wavelength of a wave is simply the length of one complete wave cycle. If you were to trace your finger across the wave in the diagram above, you would notice that your finger repeats its path.

Consider the diagram below in order to answer questions #1-2.

a. A to Cb. B to Dc. A to Gd. C to G

Indicate the interval that represents one full wavelength.

FREQUENCY AND PERIODS

•The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium.

• UNIT: Hertz (abbreviated Hz) • where 1 Hz is equivalent to • 1 cycle/second.

•If a coil of slinky makes 2 vibrational cycles in one second, then the frequency is 2 Hz. If a coil of slinky makes 3 vibrational cycles in one second, then the frequency is 3 Hz. And if a coil makes 8 vibrational cycles in 4 seconds, then the frequency is 2 Hz (8 cycles/4 s = 2 cycles/s).

PERIOD•Period refers to the time that it takes to do something.

•Period, being a time, is measured in units of time such as seconds, hours, days or years.

DIFFERENCE BETWEEN FREQUENCY AND PERIOD

PERIOD• Period refers to the time it takes something to happen.

• Period is a time quantity. • Period is the seconds/cycle.

•FREQUENCY• Frequency is a rate quantity.

• Frequency refers to how often something happens.

• Frequency is the cycles/second.

•A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance from a crest to the neighboring trough of 12.8 cm. Determine the period of such a wave.

• Answer: 0.0195 sec• Here is an example of a problem with a lot of extraneous information. The period is simply the reciprocal of the frequency. In this case, the period is 1/(51.2 Hz) which is 0.0195 seconds.

• Know your physics concepts to weed through the extra information.

•Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec.

Answer: 0.00826 secondsThe quantity 121 times/second is the frequency. The period is the reciprocal of the frequency.T=1/(121 Hz) = 0.00826 s

a. 5.0 b. 0.20 c. 0.12 d. 0.083

A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of her pacing is ________ Hz.

•Answer: D•Frequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case, there are 10 cycles per 2 minutes (also known as 10 cycles per 120 seconds). So the frequency is

• f =10 cycles / 120 s = 0.0833 cycles/s

REFERENCES• http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html• http://physics.tutorvista.com/waves/types-of-waves.html• http://

oceanservice.noaa.gov/education/yos/resource/JetStream/ocean/wave_max.htm

• http://www.physicsclassroom.com/class/waves/Lesson-2/The-Anatomy-of-a-Wave

• http://www.physicsclassroom.com/class/waves/Lesson-2/Frequency-and-Period-of-a-Wave

• http://www.physicsclassroom.com/class/waves/Lesson-2/Energy-Transport-and-the-Amplitude-of-a-Wave