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Waves!

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What is a wave? A wave is an oscillation that travels from one place to another. If you poke a floating ball, it oscillates up and down. The oscillation spreads outward from where it started.

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Waves When you drop a ball into water, some of the water is pushed aside and raised by the ball.

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Waves Waves are rhythmic disturbances that transfer energy from one place to another (caused by vibrations. i.e. water after the ball drop). Waves travel at the same speed – the speed of light. (3 x 10^8 m/s or 186,000 miles/second) Speed of sound – 340 m/s

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Parts of a wave You can think of a wave as a moving series of high points and low points. A crest is the high point of the wave. A trough is the low point.

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Parts of a wave The frequency of a wave is the rate at which every point on the wave moves up and down every second Frequency means “how often”. Unit – Hertz (Hz) means vibrations per second

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Let’s try this! If the coil of a slinky makes two vibrations every second, what is the Frequency? Answer: 2 Hz! If a woodpecker pecks at a tree 15 times a second, what is the Frequency? Answer: 15 Hz!

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Parts of a wave The amplitude of a water wave is the maximum height the wave rises above the level surface.

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Parts of a wave Wavelength is the distance from any point on a wave to the same point on the next cycle of the wave. The distance between one crest and the next crest is a wavelength.

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**A wave moves one wavelength in each cycle**

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**Transverse Wave Vibration moves at right angles to movement of wave**

Height of wave depends on amount of energy Tidal waves carry a lot of energy

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Longitudinal Wave Direction wave travels is the same direction in which the source vibrates.

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Longitudinal Transverse

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5. Wave behavior: a. Reflection - the bouncing back of a wave. 1) Sound echoes 2) Light images in mirrors

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b. Refraction - the bending of a wave caused by a change in speed as the wave moves from one medium to another.

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**c. Diffraction - the bending of a wave around the edge of an object.**

1) Water waves bending around islands 2) Water waves passing through a slit and spreading out

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3) Diffraction depends on the size of the obstacle or opening compared to the wavelength of the wave. Less occurs if wavelength is smaller than the object. More occurs if wavelength is larger than the object.

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**4) AM radio waves are longer and can diffract around large buildings and mountains; FM can’t.**

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**d. Interference - two or more waves overlapping to form a new wave.**

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**Sound waves that constructively interfere are louder**

1) Constructive (in phase) Sound waves that constructively interfere are louder

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**Sound waves that destructively interfere are not as loud**

2) Destructive (out of phase) Sound waves that destructively interfere are not as loud

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e. Standing wave - a wave pattern that occurs when two waves equal in wavelength and frequency meet from opposite directions and continuously interfere with each other. node antinode

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**f. Resonance - the ability of an object to vibrate by absorbing energy at its natural frequency.**

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