Unit 4 notes complete (1).pdf - UNIT 4 Waves and Tides WAVE ENERGY AND MOTION Book Sec5ons 4.1 4.2 and 4.3 SECTION 4.1 CAPILLARY WAVES WHAT ARE WAVES

Unit 4 notes complete (1).pdf - UNIT 4 Waves and Tides WAVE...

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Unformatted text preview: 10/7/19 UNIT 4: Waves and Tides WAVE ENERGY AND MOTION Book Sec5ons 4.1, 4.2, and 4.3 SECTION 4.1 CAPILLARY WAVES WHAT ARE WAVES? WHAT CAUSES THEM? • Waves carry energy from a disturbance across a medium through space • These disturbances are called genera5ng forces. • The three main genera5ng forces for ocean waves are wind, earthquakes, and landslides. CAPILLARY WAVES AVer the waves move away from the wind that caused them, they form swells. •  Swells are evenly spaced waves with smoothly rounded crests and troughs. •  Swells carry energy long distances across ocean basins. •  •  When wind comes into contacts with the surface of the water, the drag from fric5on causes small capillary waves to form. •  Capillary waves are the smallest of the wind driven waves, also called ripples. •  As wind grows in speed, the capillary waves get larger and the surface of the water becomes rougher. TSUNAMIS • When the seafloor is disturbed, the water above it moves up and down with the floor. This causes a large amount of water to be displaced and energy moves away from the earthquake. • Tsunamis can travel large distances and cause major damage to coastal areas. • Tsunamis do not happen with every earthquake and are difficult to track. 1 10/7/19 LANDSLIDES •  Landslides or ice breaking off of a glacier can cause major waves. This is like throwing a pebble into water and watching ripples. •  The water that was ini5ally displaced moves back to its original posi5on causing a series of waves to be dispersed. FACTORS THAT AFFECT THE FORMATION OF WAVES •  Wind Speed-­‐ The higher the speed, the larger the wave. •  Fetch-­‐ The distance of open water that the wind can blow across. Larger fetch produces more waves. •  Depth-­‐ Waves are more easily produced in shallow water than deep water. WAVE DISSIPATION WAVE DISSIPATION •  There are two types of restoring forces: •  Waves do not carry energy forever. The energy is dissipated and par5cles stop moving because they have a restoring force that causes the water to go back to its res5ng state. WAVE ENERGY •  Waves have two different types of energy: •  Poten5al •  Kine5c •  Poten5al Energy is stored based on the wave height. The higher the wave, the more poten5al energy the wave has. •  Kine5c Energy is based off of the mo5on of the water molecules. The faster they move, the more kine5c energy the wave has. •  Surface Tension •  restores small capillary waves •  Gravity •  restores large waves WAVE MOTION (ORBITAL/HARMONIC MOTION) •  Waves carry energy but not maaer. This is because a wave is just a transfer of energy. •  The direc5on that a wave travels is called the direc5on of propaga5on. 2 10/7/19 WAVE MOTION (ORBITAL/HARMONIC MOTION) •  As the energy moves through the water, the water par5cles move up and down. The par5cles then move forwards and backwards in a circular mo5on. •  This mo5on is called Orbital Mo5on or Harmonic Mo5on. •  The energy moves forward but the par5cles do not move from the orbit. WAVE INTERACTIONS When waves collide, there are two things that can happen: PARTS OF A WAVE •  Crest-­‐ highest point •  Trough-­‐ lowest point •  Amplitude-­‐ distance between the center and the maximum height. •  Height-­‐ Distance from the highest to lowest point of a wave. •  Wavelength-­‐ distance between crests •  Period-­‐ The 5me for one cycle of a wave. •  Frequency-­‐ the number of cycles per second. Parts of a Wave •  Wave Cancella5on (Destruc5ve Interference) •  The two waves will cancel each other out. •  The crest of one wave meets the trough of another wave •  Wave Reinforcement (Construc5ve Interference) •  The two waves will combine into a stronger wave. •  The crests of two different waves meet to form a much larger wave. Wavelength λ (speed of light) c λ Fig10_1a TYPES OF WAVES SECTION 4.2 CATEGORIES OF WAVES •  There are two broad categories of waves: •  Deep-­‐water waves •  Shallow-­‐water waves •  These categories depend on depth of water and the wavelength. •  Waves can transi5on between deep and shallow-­‐water waves depending on the depth of the water. •  Waves that are in-­‐between the characteris5cs of both are called intermediate waves 3 10/7/19 DEEP-­‐WATER WAVES (DWW) •  Deep-­‐water waves are waves that travel in water that is deeper than one half of its wavelength. •  The speed of the DWW depends on the wavelength, not depth. •  Progressive Wind Waves •  OVen round in oceans and large lakes •  wind generated REFRACTION AND LONGSHORE TRANSPORT •  Waves are refracted (bent) as they move from deep water to shallow water. •  This is why waves approach the shore at an angle almost parallel to the shore. •  As the waves move towards the shore, water molecules are pulled parallel to the shore. This is called longshore transport. •  This is responsible for the movement of sand and sediments. •  This is also responsible for the crea5on of ripcurrents. INTERNAL WAVES •  Waves forming under the surface of the water are called internal waves. •  They usually form in areas where water is layered in different densi5es called pycnoclines •  Internal waves vary greatly in wavelength and period. •  Internal waves are important for ocean mixing, especially in areas that have a large amount of freshwater runoff. •  They are also important in transpor5ng fish eggs from the ocean to the coastal areas. SHALLOW-­‐WATER WAVES (SWW) •  SWWs travel in water that is less than 1/20th of their wavelength. •  Wave speed depends on the depth of the water, not the wavelength. •  As the wave approaches the shore, the boaom of the ocean slows down water par5cles due to fric5on. •  As the waves slow down, the waves collide and the wavelength decreases and the waves get higher through construc5ve interference. Thus the waves eventually grow too high and crash. TSUNAMIS •  Caused by sudden movements of Earth’s crust (Earthquake/ Volcano) •  Tsunamis are seismic sea waves and can travel long distances. •  Carry large amounts of energy from displaced water. •  Can travel over 600 km/hr (Approx 373 mph). •  Can be several meters high. •  Very difficult to track •  There is no accurate tsunami warning system because they’re so difficult to track. STANDING WAVES •  Deep-­‐water, shallow-­‐water, and internal waves are progressive waves that travel in a par5cular direc5on. •  Standing waves are waves that do not progress because they’re formed in enclosed bodies of water. •  Instead of traveling, they reflect back on themselves. 4 10/7/19 STANDING WAVES •  The point around which a standing wave oscillates is called a node. •  The high and low points around a standing wave are TIDES SECTION 4.3 called an5nodes. •  They are formed because energy is reflected backwards and the waves form a stable node and an5nodes. •  The node of a standing wave usually is at the opening of a bay, which allows for minimal movement. INTRODUCTION TO TIDES • Tides are a dominant influence on nearshore sea life. • Main purposes of 5des: • Expose and submerge organisms on the shore • Drive the circula5on of bays and estuaries • Trigger spawning • Circulates food, wastes, etc. • Tides affect the nearshore areas only. They do not affect the middle of ocean basins. CAUSES OF TIDES •  Tides are very large, slow waves that travel around Earth. •  The two forces that affect the 5des: •  Gravita5onal Force (Force from Gravity) •  Centrifugal Force (Force from Rota5on) •  Tidal Periods: •  They have a wave period of 12 hours 25 min •  Tidal day is 24 hours 50 min GRAVITATIONAL AND CENTRIFUGAL EFFECTS ON TIDES •  The Moon will pull water towards it to create a high 5de from gravity. •  The Earth’s rota5on will also push water away from the moon to create a high 5de on the opposite side of earth (furthest from the Moon). •  This effect is called the 5dal bulge. TWO MAIN TYPES OF TIDES • Spring Tides • Neap Tides • These are caused by the loca5on of the Sun in rela5on to the Moon. 5 10/7/19 SPRING TIDES VS. NEAP TIDES Spring Tides: •  Sun and Moon are in line with each other. (Full and New Moons) •  Large differences between high and low 5de. •  Called spring 5des because they pop up like a spring of water. •  Not related to the seasons-­‐ they happen monthly Neap Tides: •  Sun and Moon are at right angles (1st and 3rd Quarters) •  Difference between high and low 5de is very small. TIDAL PATTERNS •  There are three main types of 5dal paaerns: •  Semidiurnal-­‐ two high and two low 5des of the same height each day. •  Mixed Semidiurnal-­‐ two high and two low 5des of different heights each day. •  Diurnal-­‐ only one high 5de and one low 5de daily (very uncommon). •  Most places have varying 5dal paaerns that shiV between the three types. TIDE LEVELS AND SEASONS •  The largest effect on the 5des is the Moon, regardless of the seasons. •  A full 5dal cycle is 29.5 days, the same as the lunar cycle. •  Tide levels change with the seasons because the distance between the Earth and Sun changes. •  During the winter in the Northern Hemisphere, Earth is closest to the sun so the sun’s effect on 5des is strongest. •  The opposite is true during the summer since the Earth is furthest away then. TIDE LEVELS •  Tide levels are measured based off of the average sea level. Thus we can have plus or minus 5des. •  A minus 5de occurs when a low 5de is below the average sea level. •  Flood Tide-­‐ Rising sea levels-­‐ beach shrinks because water is moving towards the shore. •  Ebb Tide-­‐ Lowering sea levels-­‐ beach grows because water is rushing away from the shore. •  The 5me between flood and ebb 5des is called slack water. •  These 5dal currents can be very fast and dangerous and can change the waves in an area. EFFECTS OF TIDES ON MARINE ENVIRONMENTS •  Tides help shape coastlines and beaches •  Tides help to expose and submerge organisms on the shore •  Tides help drive the circula5on of water in bays and estuaries •  Tides help trigger spawning of many marine organisms •  Tides help circulate food, wastes, etc. •  Tides help moderate temperatures in marine ecosystems •  Tides help influence the atmosphere and weather paaerns 6 ...
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  • Fall '16
  • Jane Smith

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