VEGETABLE PRODUCTION in EASTERN EUROPE

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18-1 Mechanical Waves
Wave are common and essential part of our
environment
One type of wave is mechanical wave
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18-2 Type of Waves
1. Direction of particle motion
Transverse wave
The direction of motion of the particles of the
medium is perpendicular to the direction of
propagation of the wave itself !
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Longitudinal wave
The direction of motion of the particles of the
medium is parallel to the direction of
propagation of the wave itself !
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2. Number of dimensions
Wave can be classified as propagating in
one,two,and three dimensions
3. Periodicity
The simplest periodic wave is a harmonic wave,in
which each particle undergoes simple harmonic
motion !
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4. Shape of wavefronts and waveray
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18-3 Traveling Waves
(demonstration)
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Conclusion
1.As the wave passed, the particles of medium do
not experience any net displacement with the
wave, they only oscillating about their
equilibrium positions 2.Every particle is
undergoing the same simple harmonic motion with
different initial phase (if neglect the energy
dissipation)
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If the wave moves in the negative x direction
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Sinusoid wave
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Wave number k and angular frequency ?
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If the wave moves in the negative x direction
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Transverse velocity of a particle
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Phase and phase constant
The general expression for a sinusoidal wave in
positive direction
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In the traveling wave
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If we fix our attention on a particular point of
the string , say, at a particular point x1
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Example A simple harmonic wave is propagating
toward the left direction, shown as the
figure,the wave speed is 10 m/s, the distance
between AB is 2.5m. If the equation of SHM at
point A is y A2cos(2?t ?/3), write the equation
of this wave about origin A and origin B
respectively.
Solution
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Example A simple harmonic wave is propagating
toward the left direction, shown as the
figure,the wave speed is 10 m/s, the distance
between AB is 2.5m. If the equation of SHM at
point A is y A2cos(2?t ?/3), write the equation
of this wave about origin A and origin B
respectively.
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18-4 Wave Speed on a Stretched String
Mechanical analysis
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Group speed and dispersion
The component waves travel at different phase
speeds!!
Demonstration
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18-5 The Wave Equation
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Homework Exercises 3 7 11 Problems 4 8
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Review last lecture
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In the traveling wave
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18-6 Energy in Wave Motion
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Power and intensity in wave motion
demonstration
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18-7 The Principle of Superposition
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18-8 Interference of Waves
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The phase difference between the two waves
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Exercise 21
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18-9 Standing Waves
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The amplitude 2ymsinkx has a maximum 2ymwhere
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The amplitude 2ymsinkx has a minimum 0 where
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demonstration
Reflection at a boundary
1.On reflection from a fixed end,a transverse
wave undergoes a phase change of 1800
2.At a free end, a transverse wave is reflected
without change of phase
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18-10 Standing Waves and Resonance
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Resonance in the stretched string
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Homework Exercises 20 27 Problems 13 14 15