Waves

1. Waves

2. Waves A repeating movement or disturbance that transfers energy through matter or space.

3. Rules of Waves All waves carry energy from place to place without transporting matter. • Molecules pass energy along to neighboring molecules, who then pass that energy to its neighbor…etc, so on and so forth.

4. II. Rules of Waves (cont) • All waves are produced by vibrations • Waves will travel as long as there is energy to carry • Anything that makes or responds to sound or light uses waves. • Anything that transmits information through the air without wires uses waves. • Anything that allows you to “see through” something uses waves • for example X-rays or ultrasound.

5. Waves and Oscillations • A wave is a special type of oscillation. • Remember that harmonic motion, or oscillation, is any motion that repeats over and over. • A wave is a repeating motion, or an oscillation. • However not all oscillations are waves. A pendulumswinging back and forth and a washing machine going around in circles are examples of oscillations that are not waves.

6. I. What is Harmonic Motion? Harmonic motion - This type of motion repeats itself over and over. An oscillatory fan is a great example of harmonic motion. A system that shows harmonic motion is an oscillator. An oscillation is motion that repeats itself over and over again.

7. Harmonic Motion in Our World Harmonic motion in nature Some examples of oscillation in nature are weather cycles such as el Nino. Another example of oscillation in nature is the solar system. The planets circle around the sun in a repeating pattern.

8. Harmonic motion in art and music • Both sound and light come from oscillations. Musical instruments are oscillators that are designed to create sounds with specific cycles that we enjoy hearing. Sound is an oscillation of the air. Harmonic motion in technology: • Almost all modern communication technology relies on fast electronic oscillators. Cell phones use oscillators that make more than 100 million cycles each second. FM radio uses oscillators between 95 million and 107 million cycles per second.

9. Harmonic Motion Basics • Harmonic Motion is motion that repeats itself, oscillating back and forth. • Eventually it will lose energy (called dampening) and come to rest in the middle, known as its equilibrium position. • To be harmonic motion there must be a restoring force that tries to return an object to its equilibrium position. • When a pendulum is disturbed (moved), gravity pulls down to restore the pendulum back to the center. Because of momentum, it goes past the center to the other side and back again.

10. III. Waves Around Us • We can find waves whenever information, energy, or motion is transmitted over a distance without anything obviously moving.

11. WAVES MOVE ENERGY- NOT MATTER THE BOAT STAYS IN THE SAME PLACE.

12. Medium– matter through which a wave travels. • A medium can be solid, liquid, gas or combo of these. Not all waves need a medium to travel • Electromagnetic waves do not require a medium • light and radio waves are examples of electomagnetic waves that can travel through space. *We’ll talk more about EM waves later.

13. Mechanical Waves – waves that can only travel through medium.

14. Features Of Waveshttps://www.youtube.com/watch?v=jAXx0018QCc&list=PL1Ek44JsCwBYOr8twFvQyAeO8SAOLX474

15. There are two types of waves – • Transverse waves • Longitudinal waves

16. Transverse wave • Transverse waves have oscillations perpendicular to the direction the waves move. • For example, the wave moves from left to right and the wave oscillation is up and down. Ocean waves are transverse waves.

17. Longitudinal Waves Longitudinal waves have oscillations in the same direction that the wave moves. A longitudinal wave is also called a compression wave. An example of a longitudinal wave is a slinky.

18. Wavelength – distance between one point on wave and similar point nearest to it (crest to crest, trough to trough, compression to compression or rarefaction to rarefaction) Wavelength of wave decreases as frequency increases

19. Cycles – The cycle is the building block of harmonic motion. A cycle is a unit of motion that repeats over and over; all harmonic motions have cycles. Think of the spin cycle on a blender as an example. Period (T in sec): length of time for one cycle; how long it takes for one repetition. A slower object has a bigger (longer) period Frequency – number of wavelengths that pass a fixed point each second (hertz - Hz)

20. Amplitude – a measure of energy in a wave; the more energy a wave carries greater Amplitude • Distance from crest or trough to resting position in transverse wave.

21. Calculating Wave Speed Wave speed (m/s) = frequency (Hz) x wavelength (m) v = f

22. Parts of a longitudinal wave Compressional waves have dense regions (coils close together) called compressions and less dense regions called rarefactions.

23. Amplitude – a measure of energy in a wave; the more energy a wave carries greater Amplitude • The denser the compression the larger the amplitude in compressional wave.

24. Some waves are Transverse waves • Ex.) Light Some waves are Longitudinal (compression) waves. • Ex.) Sound Some wave are both. • Ex.) Earthquake • Earthquakes are “Seismic Waves”.

25. Earthquakes Earthquakes (seismic waves) • Earthquakes are made up of both types of waves. • Longitudinal waves are the fastest and hit first,so they are called primary waves (P waves). • Transverse (T) waves are slower, but do more damage because the up and down break things by shearing (cutting), so are called S-waves.

27. SOUND, LIGHT, MIRRORS & LENSES

28. Sound

29. Sound waves compressional waves formed from vibrating objects colliding with air molecules * Remember compressional waves are made of two regions called compressions and rare factions

30. Speed of sound - depends on temperature and state of medium • sound travels faster in solids and liquids – molecules are closer together than gas molecules • as medium temp rises, molecules move faster conducting sound waves faster

31. Human Hearing • involves 4 stages: Stage 1: ear gathers compressional waves which vibrate a tough membrane called eardrum Stage 2: the middle ear has three bones called hammer, anvil and stirrupwhich amplify sound wave Stage 3: the inner ear contains the cochlea which vibrate sending auditory nerve impulses to brain Stage 4: brain decodes and interprets nerve impulses

32. Intensity amount of energy that flows through a certain area in a given amount of time Loudness human perception of sound intensity which is measured in decibels Pitch how high or low a sound seems to be which is related to frequency of sound wave

33. Music and Uses of Sound

34. Music • made of sounds that are deliberately used in a regular pattern Sound quality • differences among sounds of the same pitch and loudness - that’s why a piano sounds different than a flute playing the same note. Each instrument has a set of natural frequencies at which it will vibrate called overtones which produce an instruments distant sound quality.

35. Instruments use resonates, or hollow chambers that amplify sound when air inside vibrates. Ex. Brass & woodwinds – mouthpiece; guitars & violins – hollow body; drums – inside and sides USES OF SOUND Acoustics – the study of sound Example. concert hall engineers

36. Echolocation • process of locating objects by emitting sounds and interpreting the reflected sound waves Example. Bats Sonar • system that uses the reflection of underwater sound waves to detect objects Example. fishing boats

37. Ultrasound • high frequency sound waves Example. medicine – pregnancy, breaking up kidney stones

38. Behavior Of Waves

39. Reflection and Refraction of Light texasgateway.org/resource/electromagnetic-spectrum-introduction texasgateway.org/resource/atomic-theory-electromagnetic-spectrum

40. Objects MUST reflect light in order to be seen. Opaque does not allow light to pass through - only absorbs & reflects Translucent some light passes through Transparent transmits almost all light absorbing and reflecting little

41. Wave Interactions The four different types of wave interactions are: • Reflection - The wave can bounce off an object and go in a new direction. • Refraction - The wave can pass straight into and through an obstacle. • Diffraction - The wave can bend around or through holes in an obstacle. • Absorption - The wave can be absorbed and disappear.

42. Reflection When a wave bounces off an obstacle it is called reflection. A wave that reflects is like the original wave except it is moving in a new direction. The wavelength and frequency of the wave are usually unchanged. The reflection of a wave happens at a boundary where the wave has to pass from one condition to another. Examples of reflection are sunglasses and mirrors.

43. Law of Reflection – the angle of incidence (i) of a wave is always equal to the angle of reflection (r) https://www.youtube.com/watch?v=vt-SG7Pn8UU Reflection – occurs when a Wave strikes an object and bounces off it – all types of waves can be reflected (ex. sound, water, and light)

44. Law of Reflection • the angle of incidence (i), or where light strikes a surface, is equal to angle of reflection (r) Regular Reflection Diffuse Reflection ROCK WALL (ROUGH SURFACE) MIRROR (SMOOTH SURFACE i r

45. II. Refraction Refraction is when a wave bends as it crosses a boundary. When a wave crosses a boundary, the shape of a wave is changed. The direction of the wave usually remains the same. For example, when a wave passes through water, the wave is changed.

46. Refraction – bending of wave caused by a change in its speed as it moves from one medium to another. https://www.youtube.com/watch?v=SeaWCamCHWQ Pencil in water looks broken due to refraction * The greater the change in speed the more the wave bends

47. Refraction of light • occurs when wave of light passes from one medium to another and light wave is bent or refracted Index of Refraction • indicates how much a material reduces the speed of light; the more light slowed, the greater the index of refraction Water droplet (Rainbow) *Prisms separate white light into spectrum * Light refracted through air layers of different densities can result in mirages SUNLIGHT

48. III. Diffraction Diffraction is the process of waves bending around corners or passing through openings. Diffraction usually changes the direction and shape of a wave. Diffraction of a wave through a small opening turns plane waves into circular waves. Diffraction explains why you can hear someone even though a door is only open a tiny crack. Diffraction causes the sound wave to spread out from the crack.

49. Diffraction – an object causes a wave to change direction and bend toward it. * Both refraction and diffraction cause waves to bend however, refraction occurs when waves pass through an object while diffraction occurs when waves pass around an object