Friday, 19 September 2014
The MonSter WaVes
A
tsunami (pronounced soo-nah-mee) is a series of waves of extremely long wave
length and long period generated in a body of water by an impulsive disturbance
that vertically displaces the water. The term tsunami was adopted for general
use in 1963 by an international scientific conference. Tsunami is a Japanese
word represented by two characters: "tsu" and "nami." The
character "tsu" means harbor, and the character "nami"
means wave. In the past, tsunamis were often referred to as "tidal
waves." The term "tidal wave" is a misnomer. Tides are the
result of gravitational influences of the moon, sun, and planets. Tsunamis are
not caused by the tides and are unrelated to the tides; although a tsunami striking
a coastal area is influenced by the tide level at the time of impact.
What causes tsunamis?
Tsunamis
are most often caused by earthquakes and landslides. These push the water
upward, sideways or downward to create the tsunami waves. Volcanic eruptions
can also cause tsunamis. There is evidence than in the distant past, asteroids
and comets striking the Earth have created enormous tsunamis.
How do earthquakes generate tsunamis?
Tsunamis
can be generated when the sea floor abruptly shifts and vertically displaces
the overlying water from its equilibrium position. Waves are formed as the
displaced water mass attempts to regain its equilibrium. The main factor which
determines the initial size of a tsunami is the amount of vertical sea floor
deformation. Not all earthquakes generate tsunamis. To generate tsunamis,
earthquakes must occur underneath or near the ocean, be large and create
movements in the sea floor. All oceanic regions of the world can experience
tsunamis, but in the Pacific Ocean there is a much more frequent occurrence of
large, destructive tsunamis because of the many large earthquakes along the
margins of the Pacific Ocean.
How do landslides, volcanic eruptions and cosmic collisions generate
tsunamis?
Any
disturbance that displaces a large water mass from its equilibrium position can
generate a tsunami. Generally tsunamis caused by landslides or volcanic
eruptions dissipate more quickly than Pacific-wide tsunamis caused by some
earthquakes and rarely affect coastlines distant from the source.
How do tsunamis differ from other water waves?
Tsunami
waves are shallow-water waves with long periods and wave lengths. (A wave is
classified a shallow-water wave when the ratio between the water depth and its
wavelength gets very small. The speed of a shallow-water wave is equal to the
square root of the product of the acceleration of gravity (32ft/sec/sec or
980cm/sec/sec) and the depth of the water.) Shallow water waves are different
from wind-generated waves (the waves many of us have observed on the beach).
Wind-generated waves usually have period (time between two succesional waves)
of five to twenty seconds and a wavelength(distance between two successional
waves) of about 50 to 600 feet (15 to 200 meters) A tsunami can have a period
in the range of 10 minutes to 1 hour and a wavelength in excess of 700 km (430
miles).
Tsunami vs. Tidal Wave?
The terms 'tsunami' and 'tidal wave'
do not mean the same thing, though many use the words interchangeably. You will
find the term 'tidal wave' (referring to tsunamis) is most often see reproductions
of old news reports and older text books.
Tidal wave
1. The wave motion of the tides.
2. In popular usage, any unusually high
and therefore destructive water level along a shore. It usually refers to
either a storm surge or tsunami.
Tsunami
A
series of traveling waves of extremely long length and period, usually
generated by disturbances associated with earthquakes occurring below the ocean
floor.
Rogue wave vs tsunami?
A tsunami is caused by a sudden
displacement of water. The most frequent cause is an underwater earthquake but,
less frequently, tsunamis can be generated by volcanic eruptions, landslides,
or even oceanic meteor impact. The length of these waves, from one crest to the
next, can be up to 200 km long, and they travel in the deep ocean at speeds
around 700 km/hr. Their height in the open ocean is very small, a couple of
meters at most, so they pass under ships and boats undetected. So called 'rogue
waves' are a bit more mysterious, and not very well understood. They are very high
waves, tens of meters, perhaps. They are very short compared to tsunamis, less
than a 2000 m, perhaps. They arise unexpectedly in the open ocean, and the
generating mechanism is a source of controversy and active research. Some theories:
Strong currents interact with existing swell to make them much higher. They are
just a statistical aberration that occurs when a bunch of waves just happen to
be in the right spot at the right time, so that they add together to make one
big wave. If a storm 'prepares' the ocean, by making it very rough, and this is
followed by a sudden intensification of the storm, then the wind can get a
"better grip" on the ocean surface (i.e., wind energy is much more
efficiently transferred to the water), and the monster waves can thus be created."
What is the current tool used to detect tsunamis?
Tsunamis
are detected by open-ocean tsunami buoys and by coastal tide gages. These
instruments report their information in real-time to tsunami warning centers
(one center in Alaska, another in Hawaii,and a third to be installed soon in
Puerto Rico).
Besides the direct
observations, the amplitudes of tsunamis are also estimated from the size and
type of earthquake that may have generated them. The warning centers receive earthquake
(seismic) data from many sites as well as analyses of this information from
earthquake centers. Since seismic waves travel much faster than tsunamis, the
earthquake information is often available hours before the tsunamis are able to
travel across the ocean. This is much help for people near the earthquake,
however, since the local tsunami is there often within minutes. It is that easy
to estimate the strength of a tsunami from the character of an earthquake.
Hence, there are false alarms. It is hoped that the direct tsunami observations
will reduce the number of these. Local tsunamis are also generated by
underwater landslides and volcanoes. There is some research being done to
better understand these types of tsunamis and to develop early detection
methods for them.
References:
· http://nctr.pmel.noaa.gov/faq.php
INDUCTIVE
THINKING MODEL
Name of Student teacher: Hema.V
Standard:VIII
Subject:
Physics
Date:
Unit:
Force
Topic: Contact
and Non contact Force
|
Name of the Concept: Force
OBJECTIVES
Pupil develop observation skills
Identification of different types of forces
Generalization about the nature and characteristics
of force
Pupil develop hypothesizing predicting results
PHASE
1: Data Categorization
Teacher:
What causes the changes in the following situations like falling mango, apple,
iron pins attracted by magnet,
pushing a table, pulling a cart etc?
Student:
Force causes changes in all situations.
Teacher:
Can you suggest more situations where force is applicable in our daily life?
Student:
Yes, rainfall, pushing a door, free fall of feather, sweeping, pressing empty
plastic bottle, earth rotating, rubbing the paper, batsman striking a ball etc.
Teacher:
Can you group those examples according to their similarity?
Group A
|
Group B
|
v
Falling of mango
v
Magnet attracting iron pins at vicinity
v
Rain fall on earth
v
Free fall of feather
v
Apple falling
v
Rotation and revolution of earth
v
Ink flowing
in a fountain pen
v
Electrons revolving round the nucleus
|
v Pushing a Door.
v pressing an empty plastic bottle v pushing a table v pulling a cart v rubbing the paper v piercing nail on paper sweeping v batsman striking a ball writing |
PHASE 2:
Interpretation of data
Teacher: Let us analyze each group
of examples and know more about them. What is the peculiarity of examples in group A?
Student: In those examples there is no
physical contact between two objects
Teacher:
Yes, you are right the force applied by one body on another body without
contact and is noncontact force. What about group B?
Student: In the case of group B. force
arise as a result of contact.
Teacher:
Yes, they all are examples of contact force. Can you define contact and non
contact force?
Student: No, Teacher.
Teacher:
Force is any external effort that caused an object to undergo a certain change
either concerning its movement,
direction or geometrical construction. Can you define it now?
Student: Yes, Non contact force is force
acting on any body without any physical contact is a force that acts at that
point of contact between two objects.
Teacher: yes, you are
right.
PHASE
3:Application of generalization
Teacher:Now lets look at some more examples ,I'll give you examples of different types of forces and you must name its type.
Student: yes, teacher.
Student: yes, teacher.
Teacher:Example 1:Charging a comb by rubbing it on hair and attraction of paper bits towards it
Student: Non-Contact force. and beating a drum?
Teacher: yes,What about
Student: Contact force.
Teacher: yes,right now stitching a cloth?
Student: Contact force.
Teacher: yes,Right attraction between positive and negative charges?
Student: Non-Contact force.
Teacher: yes,Hammering a nail?
Student: Contact force.
Teacher: yes,Oscillation of pendulum clock?
Student: Non-Contact force.
Teacher: very good,and what about rotation of planets around the sun ?
Student: Non-Contact force.
Teacher: yes, and why?
Student:Teacher. There is no contact between the planets and sun.
Teacher: yes,Excellent .And What is the matter in the case where , a moving cycle is suddenly stopped.
Student: Contact force.Is,nt it teacher?
Teacher: Yes,Absolutely Correct.
So Non-Contact force is force applied on some body by another object without interaction and a Contact force is a force that acts at that point of contact between two objects.
So Non-Contact force is force applied on some body by another object without interaction and a Contact force is a force that acts at that point of contact between two objects.
………………………………………
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