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Wave Motion
In general, an oscillation or vibrating motion in which a point or body moves back and forth along a line about a fixed central point produces
waves.
How does waves transfer energy?How does waves transfer energy?
SourceOr
Disturbance Medium
Energy Transfer
•Waves are vibration that transmit energy away from an energy Waves are vibration that transmit energy away from an energy sourcesource•The energy source is often in the form of a vibration or oscillation.The energy source is often in the form of a vibration or oscillation.
The water in an ocean wave, for example, moves mainly up and down – as it passes, you bob up and down with it rather than being
carried onto the shore.
An oscillating or vibrating system acts as the source of waves which transfer energy from one point to another without transferring mass
Propagation / Travelling of Waves
1. When a wave travels through a medium, the particles of the medium vibrate about their equilibrium positions.
2. The particles of the medium do not travel in the direction of the waves.
Medium : water moleculers
Wave motion
Water waves
Disturbance
Medium
Energy Transfer
Propagation / Travelling of Waves
WavefrontWavefront
•A wavefront is a line or plane on which the vibrations of every points on it are in a phase and are at the same distance from the source of the waves AD,BE, CF the lines that join the point along the troughs of the waves.•Points in a wave are in a phase if they vibrate in the same direction with the same displacement.
wavefront
Direction of travel
A round dipper
The wavefronts of tranverse wave and longitudinal wave are perpendincular to the direction of propogation of the wave
Circular wavefrontCircular wavefront
A bar dipper
Plane wavefrontPlane wavefront
Two types of waves
Transverse waves Longitudinal waves
Transverse waves
A transverse waves is a wave in which the vibration of particles in the medium is perpendicular (at right angle) to the direction of propagation of the wave. Example : water wave, light wave and radio wave.
This animation is taken from Absorb Physics for GCSE - © Crocodile Clips Ltd. For more information, visit: www.crocodile-clips.com
Longitudinal waves
A longitudinal waves is a waves in which the vibration of particles in the medium is parallel (along) to the direction of propagation of the wave
Transverse waves Longitudinal waves
Transverse waveTransverse wave Longitudinal waveLongitudinal wave
Longitudinal waveLongitudinal wave
Wavelength
Amplitude
Frequency
Wave speed
Period
Displacement time graph
Describing wavesDescribing waves
Describing wavesDescribing waves
Wave speedWave speed
velocity of waves, velocity = frequency x wavelength
v = f
The frequency of the vibrator of a ripple tanks is 8 Hz. The wave generated has a wavelength of 0.02m.The speed of the wave is….
f = 8 Hz, = 0.02 m , V = ?
v = f
V = 8 x 0.02 = 0.16 ms-1
Sort out the jumble!
Velocity
Frequency
The speed of the wave
The number of waves per second
in m/s
in Hz
Amplitude
Wavelength in metres
Velocity
Frequency
The speed of the wave
The number of waves per second
in m/s
in Hz
Amplitude
Wavelength in metres
Answers
Wavelength
in metres
Amplitude
Frequency The number of waves per second in Hz
Velocity The speed of the wave in m/s
Reflection Refraction
Diffraction
Waves spreading out after passing through a narrow gap
Waves changing direction because of changing speed
Waves bouncing off a surface
Group the correct names, descriptions and pictures together
Reflection
Refraction
Diffraction Waves spreading out after passing through a narrow gap
Waves changing direction because of changing speed
Waves bouncing off a surface
Answers
Group the correct names, descriptions and pictures together
Factors that effect period of oscillation, TFactors that effect period of oscillation, T
Factor Period of oscillation, T
Pendulum Spring Jigsaw blade
increase
Gravitationalfield strength, gincrease
Stiffness, k increase
Mass, mincrease
Solving Problem Involving WavesSolving Problem Involving Waves
Damping and ResonanceDamping and Resonance
In an oscillating system such as oscillation of a spring, the oscillation does not continue with the same amplitude indefinitely except when the system is oscillating in the vacuum.
The amplitude of oscillation will gradually decrease and become zero when the oscillation stops. The decrease in the amplitude of an oscillating system is called damping.
An oscillating system experiences damping when its energy is drained out as heat energy.
a) External damping : loss of energy to overcome frictional forces or air resistance b) Internal damping : loss of energy due to the extension and compression of the molecules in the system.
To enable an oscillating system to go on continuously, an external force must be applied to the system. Such a motion is called a forced motion. The frequency of the system which oscillates freely without the action an external force is called natural frequency.
Resonance occurs when a system is made to oscillate at Resonance occurs when a system is made to oscillate at a frequency equivalent to its natural frequency by an a frequency equivalent to its natural frequency by an external force. The resonating system oscillates at its external force. The resonating system oscillates at its maximum amplitudemaximum amplitude
When pendulum X oscillates, all the other pendulums are forced to oscillate. It is found that pendulum D oscillates with the largest amplitude, that is, pendulum D resonates.
The frequency of a simple pendulum depends on the length of the pendulum. Note that pendulum A and pendulum C are at the same length.( same frequency ).
Lecture 23, Resonance Motion
Consider the following set of pendulum all attached to the same string
D
A
B
CIf I start bob D swinging which of the others will have the largest swing amplitude ?
(A) (B) (C)
Dramatic example of resonance• In 1940, turbulent winds set up a torsional
vibration in the Tacoma Narrow Bridge
Dramatic example of resonance
• when it reached the natural frequency
Dramatic example of resonance
• it collapsed !
Some effects of resonance in daily life:Some effects of resonance in daily life:
Trumpet Soprano
The loudness of music produced by musical instruments such as flute and trumpet is the result of resonance in the air. A soprano sings with a high note, a thin piece of glass may break. A bridge can collapse when the amplitude of its vibrationincreases as a result of resonance