Ch. 11 Waves 11.1 Nature of Waves 11.2 Wave Properties 11.3 Wave Interactions

14.1 Nature of Waves Relate waves and the transfer of energy Distinguish between transverse waves and longitudinal waves. Predict the motion of a medium as a wave of energy passes through it. Infer the energy content of a longitudinal wave. There will be a quiz at the end of this lesson (take good notes)

Waves and Energy Transfer

Wave Terms Wave - a disturbance that transfers energy through matter (a medium) or space Medium - a substance through which a wave passes (examples: sound through air, water, steel) ** Sound must have a medium to travel through. Sound waves cannot travel in a vacuum. When the fish gave energy to the cork by nibbling on the worm, that energy shows up as the ripples in the water. (What is the medium in this situation?)

Types of Waves A transverse wave is one in which the direction of the motion causing the wave is at a right angle to the direction of the motion of the wave. Direction of motion Direction of the wave 90 0

Motion of Energy

Parts of a transverse wave CRESTS TROUGHS The highest point in a transverse wave The lowest part of a transverse wave.

) ) ) ))) ) ) ) ))) ) ) ) ))) In a longitudinal wave, the direction of the motion of the wave is the same as the direction of motion of the medium. Direction of motion of the wave Direction of motion of the medium

… … … In a longitudinal wave the particles of the medium will vibrate along a line. As the wave travels through the medium these particles are close together then far apart. When particles are close this is a COMPRESSSION. When they are far apart this is a RAREFACTION. compressions rarefactions

Sound travels through a medium in longitudinal waves. How does that work? As you speak, air passes your vocal cords at certain speeds causing them to give energy to the air surrounding them. This energy is transferred to the air around your vocal cords (the medium) and through a series of compressions and rarefactions it travels through the air to your ear drum. The vibrations are picked up by your ear drum and cause the bones in your inner ear to vibrate. Your brain changes it to the sounds you hear.

) ) ) ) ) ) ) Sound actually travels in longitudinal waves in all directions.

Wave Properties Wave Behavior Are all waves the same? Actually, the size, speed, and shape of each wave are different. However, they do share common characteristics. All waves: 1. Transfer energy 2. Have height, speed, length, and frequency.

Wave Properties (cont) Line of origin crest Wave length trough Wave length Wave height

Definitions Wavelength - (transverse waves) the distance between two consecutive crests or two consecutive troughs. (longitudinal waves the distance between two consecutive compressions or two consecutive rare- factions. Amplitude - Amplitude is the vertical distance (height) between the line of origin and each crest or each trough. amplitude

Definitions (cont) Frequency - The number of wavelengths that pass a given point in a given amount of time such as per second. The unit for frequency is the hertz (Hz) 1 wave per second = 1Hz A B Wave B has a greater frequency than Wave A

Definitions (cont) Wave Speed - Frequency and wavelength determine the speed of a wave or how fast the wave approaches a given point. Formula: speed = frequency x wavelength Units: m/s = Hz xmeters Wave height - the distance from the bottom of a trough to the top of a crest.

Review Define transverse wave? Define longitudinal wave? What is a wave? Terms that go with transverse waves: crest, trough Terms that go with longitudinal waves: compression, rarefaction Define: amplitude, frequency, wave height, wave speed hertz (Hz)

Your Quiz 1. The transfer of energy through a medium is a _____________ Use the diagram above to name the parts of a wave. 7. In a sound wave where the particles of air are close together is a ___________________. 8. A _____________________ wave has rarefactions. 9. The unit for frequency is the _____________. 10. A wave with high amplitude has more / less energy than one with low amplitude. wave crest trough amplitude wave height wave length compression longitudinal hertz (Hz) -10 for each X

The end ! ! Stay tuned for 14.3 Wave Interactions