Wave Energy. A pulse is a traveling disturbance in a medium. Pictures (a) through (d) show successive positions of a pulse in a rope.

Transcription

1 Wave Energy A pulse is a traveling disturbance in a medium. Pictures (a) through (d) show successive positions of a pulse in a rope.

2 Wave Energy A wave is a succession of pulses, traveling through a medium.

3 Wave Energy Waves and pulses transmit energy, but not mass. The individual coils of a spring do not travel from one end to the other. They just vibrate in place! When we see the shape of the pulse moving, that signifies that the energy is actually being handed off from one coil of the spring to the next.

4 Types of Waves There are many kinds of waves. One type is called: transverse in which the particles of the medium vibrate at right angles to the direction the energy travels.

5 Types of Waves longitudinal in which the particles of the medium vibrate along the same line the energy travels.

6 Wave Characteristics Wavelength is the distance from crest to crest. Amplitude is the height or depth of wave, measured from the resting position. Frequency is the number of wave crests that go by each second.

7 How We Perceive Wave Characteristics Wave Characteristic SOUND LIGHT amplitude loudness brightness frequency pitch color

8 Wave Characteristics Wave speed and frequency are not the same thing! As the waves move, count the number of wave crests that pass over the vertical line. You will get two different frequencies, but the waves move together at the same speed.

9 The Wave Speed Equation

10 Units of Measurement Wave speed is measured in meters/second Frequency is measured in Hertz or cycles/second or waves/second Wavelength is measured in meters

11 Reflection Sound reflects from smooth surfaces just like light does. The angle of incidence equals the angle of reflection.

12 Refraction Refraction is a bending of the waves that is caused by changes in the density of the medium.

13 Ultrasound in Medicine A sonogram is an image made from sound waves as they reflect and refract their way through the human body. Here is an ultrasound image of a 14- week old fetus.

14 Forced Vibration When a vibrating tuning fork is placed in contact with a table, the tabletop will start to vibrate along with it. If the second object's natural frequency happens to match with the vibrations of the first, then there will be a big increase in the amplitude of the sound. The piano's sound board makes a good example.

15 Resonance Resonance occurs when the forced vibrations match an object's natural frequency. When the amplitude gets to be too great, structural failure can occur.

16 Wave Interference Two particles of matter cannot occupy the same location at the same time, but waves are different! Waves can pass through each other like ghosts. When waves come together in one place and interact, we call this wave interference.

17 Constructive Interference (a) Two upright pulses approach each other. (b) When they meet, their amplitudes add together. (c) The pulses are not destroyed. After passing through each other, they continue along their way.

18 Destructive Interference (a) Here, a crest and a trough approach each other. (b) One has a positive amplitude; the other, a negative amplitude. When they meet they cancel. (c) Again, they go through each other and continue along their way.

19 Pulse Collision When two unequal pulses meet, it's easy to see how their amplitudes add together. As always, they go through each other and continue along their way.

20 Constructive Interference Waves as well as pulses can show interference effects.

21 Destructive Interference

22 Noise Canceling Headphones A microphone inside the headphones analyzes the outside noise and generates a new wave to interfere destructively with it. As a result, the noise is very nearly canceled out.

23 Wave Interference Overlapping sets of circular waves will interfere where they cross.

24 Wave Interference The color blue identifies the lines of interference.

25 Interference in Water In this photo of water wave interference, the destructive interference regions form into lines of calm water where the waves are canceled out.

26 Interference in Water Here, the constructive interference regions show up as exceptionally high waves. They are highlighted in green.

27 Standing Waves Another example of interference can be seen when you make a standing wave.

28 New waves you send down the rope interfere with the reflected waves. Standing Waves

29 Standing Waves It is also possible to set up standing waves in a vibrating column of air. Waves interfere with each other as they reflect up and down the length of the bottle.

30 Musical Instruments Sound production from acoustic musical instruments falls into one of these categories: 1. vibrating strings 2. vibrating air columns 3. percussion

31 Multiple Harmonics

32 Musical Sounds Here is a guitar string vibrating simultaneously in the first and third harmonic. All musical sounds are composites of a fundamental tone along with a series of harmonics on top of it.