WAVES – Chpt. 14

What in the World Will I Learn? You will determine how waves transfer energy. You will learn the parts of a wave. You will describe wave reflection and discuss its practical significance.

The Big Bad Truth First! Scientists have a theory about waves and particles. What ever could this be called? Why does Mrs. Warren think this is important for me to know? Wave Particle Duality - Wave–particle duality postulates that all matter exhibits both wave and particle properties. A central concept of quantum mechanics, this duality addresses the inability of classical concepts like "particle" and "wave" to fully describe the behavior of quantum-scale objects. The idea of duality originated in a debate over the nature of light and matter that dates back to the 17th century, when competing theories of light were proposed by Christiaan Huygens and Isaac Newton: light was thought either to consist of waves (Huygens) or of corpuscles [particles] (Newton).

Wave – Particle Duality Let’s use an analogy from Leonard!

Waves If you give a rope a quick shake, it sends out wave impulses through the rope…..why does this happen?? Because you transmit energy from your body to the rope…this energy is transferred to the rope and we see waves.

WAVES a disturbance that transfers energy Carries energy from one place to another Classified by what they move through Mechanical Waves the energy is transferred by vibrations of medium (medium = matter) ex/ ocean waves move through water Electromagnetic waves (EM Waves) the energy moves through disturbances in the electromagnetic field. Physics The act or process of propagating, especially the process by which a disturbance, such as the motion of electromagnetic or sound waves, is transmitted through a medium such as air or water. A medium is a substance or material which carries the wave Big difference between mechanical and electromagnetic - An electromagnetic wave is a wave that is capable of transmitting its energy through a vacuum (i.e., empty space). Electromagnetic waves are produced by the vibration of charged particles. Electromagnetic waves that are produced on the sun subsequently travel to Earth through the vacuum of outer space. Were it not for the ability of electromagnetic waves to travel to through a vacuum, there would undoubtedly be no life on Earth. All light waves are examples of electromagnetic waves. A mechanical wave is a wave that is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another. A sound wave is an example of a mechanical wave. Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and jump rope waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium

MECHANICAL WAVES require a medium (the material through which the disturbance is moving) to transmit energy travel through & gradually lose energy to that medium Examples: water, sound, rope, & spring waves Mechanical Media: water, air, rope, spring Making a pulse Does it make sense that mechanical waves would lose energy?

Slinkin’ into Waves Working in your groups answer the following questions: 1. What do you think the difference is between a wave pulse and the wave’s vibration? Place the slinky on the floor. One person should hold one end of the slinky still, while the other person begin moving the slinky up and down. 2. What happens when you move the slinky up and down? What happens when you increase your speed? Which direction is the wave pulse? Which direction is the vibration? Again, place the slinky on the floor. One person should hold one end still, and the other person should move the slinky in a horizontal direction (it’s like giving the slinky a push). 3. Look very closely to the slinky. Do you see anything while watching the slinky? Describe what you see. Which direction is the wave pulse? Which direction is the vibration? 4. What’s the difference between the 2 types of waves you experimented with?

MECHANICAL WAVES Classified by how medium vibrates                         Classified by how medium vibrates Pulse = direction of energy transfer; more specifically, a single bump or disturbance in a medium. Vibration = direction of vibration of medium relative to pulse Longitudinal, transverse, surface 3 types:

MECHANICAL WAVES Classified by how medium vibrates Longitudinal Waves: Vibration is in the same direction as wave pulse (parallel to wave pulse) Transverse Waves: Vibration is at 900 (right angles) to wave pulse Longitudinal Waves – in a coiled spring such as a Slinkym you can create a wave pulse. If you squeeze together several turns of the spring and then suddenly release them, pulses of closely spaced turns will move away in both directions. In this case the disturbance is in the same direction, or parallel, to the direction of wave motion. Sound waves are longitudinal also liquids and gases transmit only longitudinal waves. Transverse Wave – If I have a rope and I begin to shake the rope in a vertical direction, the wave motion is in the horizontal direction. If I continue to move the rope up and down, a continuous wave is generated. Rope is disturbed in the vertical direction, but the pulse travels horizontally. Surface Waves – even though waves deep in the ocean are longitudinal, at the surface, the water moves in a direction that is both parallel and perpendicular to the direction of the wave motion. Surface waves have characteristics of both transverse and longitudinal waves. Surface Waves: Vibration is circular Ex/ Ocean waves

MECHANICAL WAVES Small Video discussing the differences between types of waves.

Surface Waves

TRANVERSE WAVES             Vibration is perpendicular to the direction of the motion of the wave S type earthquake waves

LONGITUDINAL WAVES Vibration is parallel to the direction of the motion of the wave Also called compression or pressure wave Examples: P-type earthquake waves Sound waves Rarefraction (expansion) Compression

Connecting Physics and Earth P Wave Earthquake Waves # 1 P Wave Example #2 S wave Earthquake #1 S Wave Example #2 The P waves move in a compressional motion similar to the motion of a slinky, while the S waves move in a shear motion perpendicular to the direction the wave is travelling. Primary and Secondary Waves

Waves describe the Earth P waves move through solids & liquids P waves move through solids & liquids S waves move through solids only!!! Are these MECHANICAL WAVES???? YES!! Seismic waves need a medium (the earth!)

WAVE STRUCTURE CREST (peak) AMPLITUDE resting to max peak WAVELENGTH TROUGH

AMPLITUDE Measures DISPLACEMENT Distance between “rest & crest” or “rest & trough” Gives indication of “power” or “strength” of wave (magnitude of earthquake = Richter scale) Does not affect velocity of wave Determines loudness (sound) or brightness (EM wave)

WAVELENGTH  Distance between any two repeating points on a wave (also called a cycle) crest-crest, trough-trough, expansion-expansion, compression-compression Determines what colors we see; what notes we hear (pitch) Shorter wavelengths have more cycles per minute because they aren’t as long

VELOCITY v the rate at which the energy travels; speed & direction because it’s a …. Depends on medium Mechanical waves travel faster through dense mediums EM Waves are faster through less dense mediums

Frequency ƒ How often number of wavelengths that pass any point in 1 second. measured in wavelengths/second or cycles/second Hertz (Hz) = number of wavelengths in 1 second Frequency is related to velocity and wavelength: v = ƒ 

PERIOD T How long Amount of time for one wavelength to pass a point Related inversely to frequency Period = 1 Frequency When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period. 1 = 1 T f

Example Time!  A sound wave has a frequency of 262 Hz and a wavelength measured at 1.29 m. Part a) What is the speed of the wave? Part b) How long will it take the wave to travel the length of a football field, 91.4 m? Part c) What is the frequency of the wave? Let’s break it down ya’ll!

Example Part a A) What is the speed of the water? frequency = 262 Hz, wavelength = 1.29 m v = ƒ  Which variable are we solving for? Let’s plug it in!! V = (262 Hz)(1.29m) = 338 m/s

Example Part b How long will it take the wave to travel the length of a football field, 91.4 m? V = d/t We know velocity, we know distance, we don’t know time. 91.4 m / t = 338 m/s T = 0.270 seconds

Example Part c Find the frequency from the period. We knew period, we know the equation, we need to find frequency. T = 1/f T = 1/262 = 0.00382 seconds