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Lecture

Biogeochemical cycles Part 2.docx

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Department
Natural Science
Course
NATS 1840
Professor
Carl Wolfe
Semester
Fall

Description
Biogeochemical cycles Part II – Energy Work: Work is said to be done when matter moves as a result of the application of a force upon it. (There has to be some force involved in order for work to be done; if there is no motion no work is done) Energy: The ability of a system to move matter through some distance. Ie. The ability a system to perform mechanical work. Forms of Energy: Energy comes in several different forms. Some are closely associated with tangible physical objects, such as atoms. Other forms, such as the energy carried by light, are less tangible. - We will be mainly concerned with o Kinetic energy o Potential and internal energy o Thermal energy o Electromagnetic energy Kinetic Energy: energy is associated with motion. A moving object has the ability to do physical work. For example in a collision. Intutively, a faster object can do more work than a slow moving object and a more massive object can do more work than a light object.  Kinetic energy increases with speed and mass Potential Energy: represents the ability to do work that is stored in a physical system that isn’t in motion. There are many ways to store energy: - Height above ground (gravity): - Bending of a solid object (elastically): - Difference of electric charge between objects (electricity) (Battery, electric generator) - Binding of two or more atoms (chemical energy) Stored energy is the result of mechanical work that was done against a force at some prior time. Thermal Energy: Energy associated with heat. Associated with the random motion of the molecules making up a substance is called thermal energy. It is also called heat. Temperature is a measure of the average amount of thermal every per molecule in an object. More thermal (kinetic) energy Faster moving molecules Hotter object How does a thermometer measure thermal energy? - Suppose a fast moving molecule in a hot object collides with a slow moving molecule in a cold one. The collision transfers thermal energy to the slow molecule, and thus to the cold object. (in a microscopic object there are always collisions occurring) - Thermal energy flows form hot to cold until both objects share the available thermal energy equally. After this there is no longer any net every transfer between the objects. A steady state is reached and both objects have the same temperature. Thermal Energy A thermometer is initially either hotter or colder than the object whose temperature it is to measure The HOT thermometer reading stops COLD changing when the average thermal energy per molecule in the thermometer is the same as that in the object being measured In other words, the steady state thermal energy of the thermometer reflects the thermal energy of the object under study. Electromagnetic waves: The kinetic energy of a piano hammer is transferred to the struck string, which starts to vibrate and sets the surrounding air into motion. A pressure wave is created, which our ears interpret as sound. Similarly, vibrating electric charges cause vibrations in the surrounding electromagnetic (EM) field, creating a EM wave which moves away from the vibrating charge. Vibrations of the EM field carry energy just as sound waves do. EM waves travel at the speed of light (3c 10^3 m/s in vacuum). Any given EM wave has a specific frequency and wavelength. Electromagnetic Energy Wavelength: the distance in space between successive cycles. Frequency: the number of full cycles of the wave passing a fixed point in space each second. Frequency and wavelength are related in such a way that Higher frequency Shorter wavelength Greater Energy The energy carried by an EM wave depends on the frequency (wavelength) of the oscillations, with higher frequencies (shorter wavelengths) corresponding to greater energy. The electromagnetic Spectrum The motion/vibration of a charged particle creates an E.M wave (ie. The charge does work on the ambient EM field) An EM wave can do work on a charged particle, setting it into motion. Heat and Electromagnetic Radiation: Heat and EM radiation are intimately connected in a way that is crucial to understand climate and climate charge. Consider a rock exposed to sunlight. It absorbs EM energy continuously. - The rocks molecules speed up - The rocks thermal energy (temperature) increases.
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