NS1300 – Emergence of Modern Science Energy and Thermodynamics

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Where does our energy come from, and will there be enough in

the future?

History of Energy

• How much energy did we need before the bronze age?

• How much energy did we need before the industrial revolution?

• How much energy do we need now?

• How much energy will we need in the future?

Energy• Mechanical Energy

• Thermal Energy

• Chemical Energy

• Electromagnetic Energy

• Entropy

The 1st law of Thermodynamics

• The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings.

• Heat is a process by which energy is added to a system or lost to a sink.

• Energy is lost to a system by doing mechanical work.

• Energy is always conserved between a system and its surroundings.

Law of Conservation of Energy

• Energy is Neither Created nor Destroyed

– Enthalpy: H = U + pV

– H is the enthalpy– U is the internal energy – p is the pressure of the system – V is the volume

– Entropy: S = k log W

– W is the number of microstates corresponding to a given macrostate– K is Boltzmann’s Constant

• Open Systems and Closed Systems

– The Universe is the Only Closed System in Nature

The 2nd Law of Thermodynamics

• In an isolated system, a process can occur only if it increases the total entropy of the system.

• Heat cannot spontaneously flow from a material at lower temperature to a material at higher temperature.

• It is impossible to convert heat completely into work.

Applications of Entropy

• Engineering– Mechanical– Chemical– Electrical

• Biology

• The Environment

Energy Conversion

• Any form of energy can be transformed into any other form

• Energy is the Ability to Do Work

Work

• Work = Force X Distance (W = Fd)

• Simple Machines

Mechanical Energy

• Potential Energy

– PE = -G(m1m2/R)

• Kinetic Energy

– E = 1/2mv2

Thermal Energy

• Thermal Energy

• Heat

• Temperature

• Calories

Thermodynamics• Thermal Energy

– The internal energy of a system associated with kinetic energies of the molecules:

• molecular translation, • rotation, and • vibration• electron translation and spin • nuclear spin

– and the phase of the system.

Heat and Temperature• Specific Heat

• Latent Heat

• Molecular Kinetic Energy

• Temperature Scales– Fahrenheit– Celsius– Kelvin

• Absolute Zero

Flow of Heat

• Radiation

• Conduction

• Convection

Heat Budgets

Heat Budget of the Atmosphere and Ocean: QT = QSW + QLW + QS + QL + QV

Thermoregulation

Efficiency

• Engines

• Systems

• Organisms

Power

• Power = Work / Time (P = W/t)

Power Sources

• Solar

• Fossil Fuels

• Electricity

• Batteries

Future Energy Sources• Wind

• Geothermal

• Nuclear

• Biofuels

• Hydrogen

Misconceptions About Entropy

• Zero Point Energy

• Tachyons?

• Perpetual motion

• Pseudoscience?

Quiz• 1. T or F, energy is the ability to do work.

• 2. T or F, any form of energy can be converted to any other form of energy.

• 3. Simple machines make work easier, but less efficient. Name a simple machine.

• 4. T or F, photons can cause electrons to flow through a circuit.

• 5. T or F, zero-point energy is a viable alternative source of energy for the future.

Test Questions• Energy is the capacity to do work. Potential Energy = the potential to do work. Kinetic Energy =

the energy of motion (momentum).

• Any form of energy can be converted to any other form of energy. All energy can be accounted for in a closed system (in other words, energy is conserved). Entropy describes the total energy of a system and tells us that we cannot get more energy out of a system than we put into it.

• W = Fd; Power = W / t; Simple Machines make work easier by changing the distance through which force is applied.

• Thermal energy is the internal and external energy of atoms. Heat is the transfer of thermal of energy between atoms. Temperature is a measurement of the kinetic energy of molecules.

• Adding heat energy to substances makes their temperature rise (specific heat). To change the state of a substance requires even more heat energy (latent heat).

• Heat can be transferred by radiation, conduction, and convection.

• Organisms transfer energy through trophic chains. The higher you are on the food chain, the less efficient you are in converting the energy contained in your food into work (activity; yes, thinking is activity).