Lab 5 WAVES

What is waves ? how do waves form? Wave is a movement of upper surface of water due to transfer of energy from the wind into the water without transfer of particles. Caused by : a) Wind b) Earthquakes c) gravitational force of the moon and sun

How do wave form Although waves may appear to carry water forward shore, the water does not actually move forward in deep water. if it did, ocean water would eventually pile up on the coasts of every continent! the energy of the wave moves forward shore, but the water itself remains where it was. wave do not carry water, they carry energy. As the energy transferred from the wind to the water increases, the height and steepness of the waves increase as well.

Types of waves (1)Progressive wave = travelling wave, transfer energy from one place to another. (2) standing waves= do not progress, they are reflected back on themselves and appear as alternating troughs and crests at a fixed position called antinodes, oscillating about a fixed point called node. They occur in ocean basins, enclosed bays and seas, harbors and in estuaries.

-Wave particles move in a circular motion ( orbital motion ). -The diameter of the orbital motion decrease with the depth of water. -The orbit diameter = wave height - Wave base : the maximum depth to which a passing wave imparts motion to the water. - Wave base = ½ L

Progressive wave classification Depends on their wavelength relative to the depth of water through which the wave are passing.

Wave Parameters

Activity 1 What is the highest part of the wave? What is the lowest part of the wave? What is the distance between two crests or troughs ? What is the vertical distance between a crest and trough? What is the vertical displacement of the crest or trough from the undisturbed water level ?

Measuring waves

wave stability or steepness 1 high 120˚ 7 across

when wind blows a cross a body of water, the friction causes the water to move along with the wind. Factors affecting wave height: 1. wind speed. Measured in knots or nautical mile per hour. 2. Duration : length of time the wind has blown. Wind in some areas blow strong for long periods od time which can produce large waves. 3.Fetch : distance over which the wind blows. The longer the fetch, the bigger the wave, the more power of wave to erode. If the wind blows hard enough (speed) and long enough (duration) over a long enough area (fetch), waves become fully developed. When the wind stops, they become swells. As swells reach shore they change into breaking wave ( white caps ). Factors affecting wave height:

Activity 2 Please review the following illustration, and answer the questions. 1. What happens to wavelength as deep water waves become shallow water waves? 2. What happens to wave height as deep water waves become shallow water waves? 3. What happens to wave period as deep water waves become shallow water waves? 4. When the water depth is one-half the wavelength of a deep-water wave, water particles just above the bottom follow what kind of a path?

When waves meet up, they interfere with one another Wave interference can be : 1. constructive interference occurs when like parts of wave coincide.when crest overlap or trough overlap the resulting composite wave will be total height of both ex: one wave height is 2ms, and the other wave height is 3ms, the composite wave height is 5ms. 2. destructive interference occurs when dissimilar parts of waves coincide. The resulting composite wave will be subtracting the two height of waves ex: if both waves have a wave height of 3ms, the water surface will remain flat. Progressive Wave interference

Activity 3 a b 21 Write the wave interference type based on the wavelength overlapping each other

Progressive Wave refraction As waves approach shore, they bend so wave crests are parallel to shore. Notice : Wave refraction strongly influences erosion and deposition

Wave approach shore transitional wave shallow water wave wave speed decrease wavelength decrease wave height increase wave steepness increase waves break period remains constant.

Field assignment 1. you are going to measure wave length, height, period and speed for waves in shallow water. 2. find a beach that is protected that you can go out beyond the surf zone without having to swim. 3. Two students go out their, taking a meter stick and a rope with you. 4. With the meter stick, estimate the average height of the incoming waves and the average depth of the water where the two of you are. 5. With the rope, estimate the wave length. 6. Measure the wave period, i.e. the number of seconds that it takes a complete wave ( from one crest to the next) to pass one of you. 7. make several measurements of each and average them. 8. Calculate the wave speed from your data ( wave velocity). 9. Calculate the theoretical shallow water wave speed ( velocity ) for the depth that you measured, using V= 3.13 √d, where d is the water depth in meter and V is the wave speed ( velocity ) in meters/second 10. How does this compare to the waves you measured? Where your truly shallow water? ( i.e. was the depth less than 1/20 the wave length?

Measuring of wave parameters & velocity St.Crest reading Trough reading Depth (m) Wave height Wave length Wave period Practical wave velocity(m/sec) Theoretical wave velocity (m/sec) #C ( m)T (m) C+T/2C-T (m)L (m)secL/time ( period)V=3.13√d