Forces, Energy and Power
- forces: act on a body
- energy: work done on a body or the capacity to do work
- power: energy spent in a certain time
Basic Types of Energy that Fuel Natural Disasters
| type | definition | natural disaster |
|---|---|---|
| potential | energy stored in a system resulting from a relative position to a reference point (gravitational potential energy; depends on distance to reference body and mass) or from the state of a system (elastic potential energy; depends on deformation and resistance to deformation) | impactors in Earth's gravitational field; unstable masses prone to landslides, volcanic material ejected into the atmosphere, earthquake faults, plate tectonics | kinetic | energy of motion (depends on speed and mass of body) | meteorite impact, landslides, volcanic explosions, lava flows, pyroclastic flows, earth movement resulting from earthquakes, wind storms |
| rotational | circular motion (depends on moment of inertia/resistance to change in angular velocity); orbiting (e.g. Moon around Earth); rotating (e.g. Earth) | tornadoes, some types of landslides, rotating storms |
| heat | internal: produced by radioactive decay inside Earth or primordial heat; external: sun | internal: volcanoes, plate tectonics external: atmospheric processes; severe weather |
Heat: Earth's Internal Sources of Heat
- impact energy during formation
- energy from initial gravitational compression and contraction
- early differentiation (sinking of heavy elements released potential energy)
- decay of radioactive elements/fission (splitting of atoms); process still ongoing!
Heat: External Sources of Heat
- now, sun as principal source
- Earth's surface receives 5300 more heat from sun than from within
- sun's heat generated by fusion (combining atoms)
- locally, impacts from extraterrestrial bodies (transfer from kinetic energy to heat)
Transfer of Energy between Different Types
- potential to kinetic: mass moving down a slope; snapping of loaded spring; earthquakes
- potential to rotational: round body moving down slope
- kinetic to potential: lava bombs ejected from a volcano
- kinetic to heat: impact
The 4 Ways to Transport Heat
- conduction: no mass transport; kinetic energy passed between vibrating atoms
- radiation: no movement of mass at all; heat passed as electromagnetic waves
- diffusion: migration of single particles (e.g. atoms or dust) that carry heat with them
- convection: mass transport! moving mass carries heat with it; most effective mechanism to transport heat
Viscosity and Mantle Convection
- viscosity: the resistance of a material to flow; high viscosity: material is difficult to deform; low viscosity: material deforms/can flow easily
- mantle is made of hard rock which is ductile (i.e. flows) over geologic times
- mantle deforms, convects and turns over (at rate of few cm per year)
- convection driven by heat and/or density variations
- speed controlled by viscosity (resistance to flow)
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DID YOU KNOW? Assuming a velocity of 10cm/yr, it would take nearly 60 Mio years (million) for a piece of lithosphere to travel from the surface to the core-mantle boundary and back. |
The Concept of Latent Heat
The concept of latent heat is very important as big storms are fueled by the immense amounts of energy stored in water vapor in the form latent heat.
The Phases of H2O
- H2O has 3 phases:
- ice (solid)
- water (fluid)
- water vapor (gas)
- Energy is either taken up or released when going from one phase to another.
Heat Capacity
| material | heat capacity [cal/cm3°C] |
| air | 0.0003 |
| quartz sand | 0.31 |
| granite | 0.52 |
| aluminum at 20°C | 0.58 |
| copper at 20°C | 0.82 |
| glass at 20°C | 0.5 |
| human body(1) | 0.8 |
| water | 1.0 |
- water has high heat capacity (Table 2.1): it takes a lot of heat to increase T
- oceans therefore serve as climate moderators
Oceans take a long time to warm, but also to cool. Costal areas therefore experience a milder climate than inland areas.
Latent Heat
- latent: from the Latin word latere for "to lie hidden"
- latent heat is energy stored in a system that is not "sensed" immediately but can be used in a process
- latent heat is released or taken up in phase changes
- phase change from liquid to gas: evaporation: energy taken up as latent heat (latent heat of vaporiation); condensation: latent heat released
- phase change from solid to liquid: melting: energy taken up (latent heat of melting); freezing: latent heat released
Uptake and Release of Energy during Phase Changes
- it costs heat to turn water into water vapor (evaporation from oceans, lakes, rivers)
- ~600 cal per 1 g of evaporated water
- this energy stored in water vapor as latent (hidden) heat
- evaporation has a cooling effect on the surface water left behind
- evaporation: air containing water vapor gains energy
- condensation: air containing water vapor loses energy
- condensation causes clouds, fog and rain to form
- latent heat released during condensation can drive severe weather and storms
Recommended Reading
- "Category 7" by Bill Evans and Marianna Jameson; ISBN: 978-0765356710; list price: $7.99. This is a science-based FICTION story about a scientist-gone-crazy who tries to manipulate the size and the path of a hurricane. The story is about how a hurricane can be fed, i.e. it's latent heat increased by a secret laser weapon. The author is a meteorologist so knows a thing or two about weather. The really interesting thing about this book is that it also talks about past (REAL!) efforts in the U.S. to control/manipulate weather and the consequences of an attempt in 1947 to divert a hurricane before it made landfall in Georgia (Project Cirrus). Project Cirrus was superseded in 1992 by Project Stormfury that was considered to be a failure. More recent cloud seeding attempts in China to increase rainfall are thought to have contributed to unusually severe snowstorms.