Chapter 13

13.1 Special Wiggles – Vibrations and Waves When something moving back and forth, side to side, or up and down we say it vibrates. When that vibration moves through space and time we call it a wave. Waves are rhythmic disturbances that carry energy through matter or space

Light and Sound both travel as a wave but they are two very different types of wave. Sound requires matter to move through to transport energy from one place to another Light can travel through space with out any matter to move through. It can even pass through many materials

Wave Characteristics

13.1 Special Wiggles – Vibrations and Waves A: Resting point; this is where the wave starts from. B: Crest; this is the highest point of the wave. C: Wavelength (λ); the distance from one crest to the next one

13.1 Special Wiggles – Vibrations and Waves D: Wavelength; wavelength can also be the distance between any two identical parts of the wave E: Amplitude; the distance from the resting point to the crest. F: Amplitude; amplitude can also be the distance from the resting point to the trough

13.1 Special Wiggles – Vibrations and Waves G: Trough; the lowest point of the wave

13.1 Special Wiggles – Vibrations and Waves Frequency: How often the wave or vibration passes a point in one second. The symbol for frequency is f The unit for frequency is hertz (Hz) One hertz is one vibration per second

Period: The time it take for one complete vibration or one complete wave (crest and trough) to pass a point. The symbol for period is T. –T–Think of is as a special unit of time The unit for period is seconds

Period can be calculated from frequency and vis-versa Suppose a 2 waves passes a pole every second. This would make the frequency 2 Hz. This means the period of the wave is ½ seconds or a half a second. It takes a half a second for one complete wave to cycle through

13.2 Wave Motion – Transporting Energy When a wave moves through matter it carries energy It does not, however, carry the matter with it. –A–A wave moving past a bobber moves the bobber up and down but does not move it in the direction of the wave. –Y–You don’t feel sound waves from someone speaking because the air that is carrying the sound is not moving to you.

Because waves move we often need to know the wave speed. Wave speed is related to the frequency and the wavelength of the wave. Remember speed is

Wavelength is measured in meters which is the distance between the crests of the waves Frequency is equal to And Period is measured in seconds which is the time for one wave to complete its cycle or one wavelength to pass Wave speed is measured just like any other speed in m/s

Try it! A wave travels past the bird 3 time every second. It has a wavelength of 1 meter. What is the wave speed?

13.2 Wave Motion – Transporting Energy Wavelength = 1 m ; f = 3 Hz Wave speed Wave speed = wavelength x frequency Wave speed = 1m x 3 Hz Wave speed = 3 m/s

13.3 Two types of waves – Transverse and Longitudinal Transverse Waves –T–The medium vibrates in a perpendicular direction of the vibrating source –D–Describing Transverse waves Crests – the highest point of the wave Troughs – the lowest points of the wave Wavelength – the distance from crest to crest Amplitude – the distance from the crest to the resting position Frequency – the number of wave crests that pass a certain point each second. –E–Examples Light Water Waves Waves in a guitar string

Longitudinal Waves –T–The medium vibrates in the same direction as the vibrating source –D–Describing Longitudinal Waves Compression – the dense area of the wave Rarefaction – the less dense area of the wave Wavelength – One compression and one rarefaction Frequency – The number of compressions that pass a point each second. –E–Examples Sound

A: Longitudinal Wave B: Transverse Wave