Waves & Vibrations

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Big Ideas: Wave, Transverse, Longitudnal, Wave Speed, Frequency, amplitude, Sound, Natural Frequency, Resounance.

Waves are a wiggle in space cause by a vibration or disturbance. They have the ability to carry energy from one location to another. There are two different types of waves; transverse and longitudinal. A transverse wave is when the wave is vibrating perpendicular to the direction the wave is traveling. A longitudinal wave, also called a compression wave, is a wave in which the vibration is in the same direction as that in which the wave is traveling.

How frequently a wave or vibration occurs during a span of time, determines the waves frequency. Frequency is the number of waves per unit time. The unit for frequency if a Hertz ( 1/second). The speed a wave travels is the wavelength multiplied by this frequency. The amplitude of a wave is the maximum distance the wave is displaced.

Waves are characterized by several distinct behaviors. One behavior is interference. Wave will combine with each other, causing an interference. There are two types of interference. Constructive interference is when two or more waves combine, and the amplitude of their resultant wave increases. Destructive interference is when two or more waves combine and the amplitude of their resultant wave decreases. Waves will also diffract. Diffraction is the bending of waves when they hit a barrier.

Sound is the result of vibrations in molecules causing the molecules to compress and retract, making sound a longitudinal wave. The vibrating source must push some material (medium, e.i. air, metal, water)

for the sound wave to travel. Therefore sound cannot travel in a vacuum where there is not matter. The frequency and amplitude of sound waves have subjective qualities: frequency relates to the pitch of a sound while amplitude relates to the loudness.

All material objects can vibrate to make a sound. The neat thing is all objects will naturally vibrate at a certain particular frequency. This is called the natural frequency . An example would be a big thick guitar string would vibrate naturally at a low frequency. A smaller, thin guitar string would vibrate at a high frequency. Usually (not always) larger and longer objects have lower natural frequencies, while smaller and shorter objects have higher natural frequencies. All objects have a natural frequency.

If you push something to vibrate at its natural frequency and keep pushing it at just that right rhythm, you can get it to vibrate like crazy – it will make a louder and louder sound. You can also get it to vibrate so much it breaks. When you push something at its natural frequency it's called resonance .

Resonance involves matching frequencies. Let's say you're playing some music on a stereo and occasionally something else in the room vibrates – like a vase – this is an example of resonance. At a given moment frequencies of the sound waves in the music matched the natural frequency of the vase – and the vase resonated, that is it vibrated with an increased amplitude.

 Experiences Patterns Explanations A slinky given two pulses in the same direction from opposite ends A slinky given two pulses in the opposite direction from opposite ends.   Giving consecutive pulses on a slinky with a fixed end.   Increasing the frequency of a standing wave on a slinky. (The speed of the wave stays the same) When the pulses met in the middle, the amplitude increased. When the pulses met in the middle, the amplitude decreased.   There become place that stand still and places that move back and forth. As the frequency increases, the length of the wave decreases. Waves will add together, resulting in an increased or decreased amplitude.         Wave speed = frequency * wavelength

Objectives

• Identify wave characteristics of frequency, wavelength, wave speek, and amplitude
• Identify and describe examples of longitudinal and transverse waves
• Describe the behavior of waves when they interact; constructive and destructive interference, standing waves
• Explain the Doppler Effect
• Relate characteristics of sounds that we hear to properties of sound waves
 Monday Tuesday Wednesday Thursday Friday President's Day. - No School Jounal: Monster Ocean Waves No Journal no class No Journal Activites: Activites: Finish Waves & Vibrations Lab Turn in: Wave lab Follow up Bonus Option Read pg 335 and answer practice problems 1-4 Activities Wave Quiz Wave Notes Notebook Check