1. Physics of Tsunamis Part 2: Conservation of Energy

2. Review from last week  How are waves created?  Types of waves?  What are water waves?  Wave features?  Homework?

3. Energy principles  Energy - the capacity of any system to do work.  Work: Magnitude of the displacement times the component of the force parallel to the displacement  Potential energy - energy any system has as a virtue of its position E P =mgh  Kinetic energy - energy any system has as a virtue of its motion E K =1/2 mv 2  Mechanical energy - energy related to motion and position E=E K +E P

4. Check your understanding  How does the rollercoaster ride illustrate mechanical energy?  If the acceleration of gravity value of 9.8 m/s 2 is used along with an estimated mass of the coaster car (say 500 kg). If the height at the starting position is 72m, what is the height of the of the first loop? (When the car is upside down its speed is 25m/s). h=40m

5. Creation of tsunami

6. Tsunami’s potential energy  An earthquake is a vibration of the Earth’s surface. Earthquakes do work on the sea floor creating tsunami waves.  Displacement of water caused by an earthquake will rise the water above the sea level. The amount of water lifted above the sea level is tied up to gravitational potential energy.  Once the waves are created, energy of water waves is transmitted as kinetic and potential energy.  Tsunami wave moves the entire depth of the ocean, rather than just the surface. This means it contains an enormous amount of energy, allowing it to travel great distances at high speeds. As the wave travels, the energy, is spread over a larger and larger area.

7. Transformation of Kinetic Energy into Potential Energy at Shore  At high speed tsunamis build up a high kinetic energy.  When tsunami wave reaches the shore its speed and wavelength decreases which decreases kinetic energy.  When the wave slows down in a shallow water some of the kinetic energy is lost. From conservation of energy we know that this kinetic energy is transformed into potential energy.  Potential energy is increased by increasing the height of the wave.

8. Speed of water waves  Near the earthquake epicenter wavelength of tsunami wave can be around 150km.  A typical ocean depth is 4km, and wave speed is in order of 200m/s ~ 720km/hr (450mph)  Speed of sound in air is in the order of 340m/s

9. Compare the energies  Airbus A380 crashing in the water at the full speed E=2.5 x 10 12 J  Hiroshima atomic bomb, World War II E=6.3 x 10 13 J (25 times more than A380)  Indian Ocean Tsunami, 2005 E= 2 x 10 18 J (32,000 atomic bombs)