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Force and Motion Ophir Ortiz and Souheil Zekri Standard 1: 2. knows that waves travel at different speeds through different materials

Why are waves important? • Waves are • Waves transmit energy that topple buildings during earthquakes Figure 1: Seismogram • Figure 2: Satellite Our observations from earth to space are dependent on waves received by satellites

Outline • • Definition of a wave Characteristics of waves Examples of waves Activity

What is a wave? • Definition: A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself • In simpler terms, a wave may be described as a ripple or an undulation

Stadium wave http: //www. colorado. edu/physics/2000/waves_particles/stadium_wave. html

Characteristics of Waves • The characteristics of a waveform are: • wavelength (period) • amplitude • velocity • frequency • All periodic (repeating) waveforms have these common characteristics

Wavelength • Wavelength is defined as the distance from one crest to the next crest. • The wavelength of an ocean wave: • several meters. The wavelength of the electromagnetic wave used in a microwave oven: ~ 1 centimeter.

Wavelength Applet

Amplitude A • The height of the wave is called its amplitude. • Amplitude relates to loudness in sound (for a sound wave) and brightness in light (for an electromagnetic wave).

Velocity • The velocity of the wave is the measurement of how fast a crest is moving from a fixed point. • The speed of sound is about 1000 feet/second. • The speed of light is 2. 99 x 108 meters/second.

Frequency • The frequency of waves is the rate the crests or peaks pass a given point. Cycles per second is also called Hertz. Frequency = Velocity / Wavelength

Classification of Waves Mechanical Electromagnetic Longitudinal Transverse Torsional Classification according to medium through which wave travels Classification according to wave orientation

Mechanical Waves • Matter is the medium • Sound is a mechanical wave

Electromagnetic Waves • Electric and magnetic fields are the • media Light is an electromagnetic wave

Longitudinal Waves • A sound wave is a classic example of a longitudinal • wave As a sound wave moves from the lips of a speaker to the ear of a listener, particles of air vibrate back and forth in the same direction and the opposite direction of energy transport http: //www. glenbrook. k 12. il. us/gbssci/phys/Class/sound/u 11 l 1 a. html

Transverse Waves • Disturbance is perpendicular to the direction of propagation Perpendicular: Two lines that meet at a right (90°) angle • All electromagnetic waves are transverse. This includes light.

Transverse Waves • Particles vibrate at right angles to the direction of the wave's velocity Example: waves along a string PARTICLE DISPLACEMENT 90° VELOCITY http: //online. cctt. org/physicslab/content/Phy 1/lessonnotes/waves/lessonwaves. asp

Torsional Waves • waves which twist about a central axis

Tacoma Bridge

Sound Waves • Sound is a waveform that travels through matter • Sound will readily travel through many materials • Speed of sound through air depends on: – density of the material – temperature Material Air Velocity m/s 331 Water (50°C) Brass 1540 Aluminum 6400 4490