Introduction to Energy and Conservation

Defining Energy

• Energy, a fundamental concept, is defined as the ability to do work.
• Energy exists as kinetic, potential, thermal, electrical, chemical, and nuclear forms.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy, able to do work.
• Thermal energy relates to temperature.
• Electrical energy is the flow of electric charge.
• Chemical energy is stored in molecular bonds.
• Nuclear energy is stored within an atom's nucleus.
• Energy can be transferred or converted, but within a closed system, the total energy remains constant.
• The principle of energy conservation is a foundational law with broad implications.
• Work is the transfer of energy from one object to another.
• When work is done on an object, its energy changes
• Applying force to move an object increases its kinetic energy. Conversely, when an object does work, its energy decreases.

The Principle of Energy Conservation

• The principle dictates that the total energy in an isolated system remains constant over time.
• Energy is neither created nor destroyed, only transformed or transferred.
• This principle applies universally from subatomic particles to galaxies.
• ΔE = 0 mathematically expresses energy conservation, where ΔE is the total energy change in a system.
• In a closed setup, any increase in one form of energy must proportionately reduce another, keeping the total constant.
• Energy conservation helps in understanding and predicting physical systems, in mechanics or thermodynamics.
• In a roller coaster, potential energy converts to kinetic energy as it descends, with total energy constant, if ignoring friction and air resistance.
• In chemical reactions, energy in reactant bonds changes to other forms, like heat and light, conserving the total energy.

Energy Conservation in Medical Physics

• Energy conservation is vital in medical physics, impacting radiation therapy, imaging, and nuclear medicine.
• Radiation therapy relies on understanding energy transfer and absorption to deliver radiation to tumors while protecting healthy tissue.
• Medical physicists calculate energy deposited by radiation beams for accurate and safe dosage.
• In X-rays, CT scans, and MRI, energy conservation optimizes image quality and minimizes radiation exposure.
• Adjusting the energy of X-ray beams maximizes tissue contrast and minimizes overall radiation to the patient.
• Nuclear medicine uses radioactive isotopes for diagnosis and treatment.
• Medical physicists ensure safe and effective use of isotopes, considering the energy released upon decay.

Energy of Interacting Bodies

• Energy exchanges occur when bodies interact, changing individual energy states through collisions, forces, and fields.
• In interacting systems, total energy remains conserved, although individual energies might change.
• In a collision of billiard balls on a frictionless table, kinetic energy transfers, but the total kinetic energy remains constant.
• Gravitational or electromagnetic forces can also mediate energy exchange.
• When an object falls under gravity, potential energy converts to kinetic energy.
• Electric and magnetic fields mediate interactions, changing kinetic energy.

Potential Energy

• Potential energy is stored energy due to an object's position or configuration, convertible into other forms like kinetic energy.
• Types include gravitational, elastic, and chemical potential energy.
• Gravitational potential energy is based on height relative to a reference point.
• When an object falls, gravitational potential energy converts to kinetic energy, causing acceleration.
• Elastic potential energy is stored in deformable objects when stretched or compressed.
• Releasing a stretched rubber band converts elastic potential energy into kinetic energy, propelling it.
• Chemical potential energy is stored in molecular bonds and released during reactions like combustion or metabolism.
• Gasoline's chemical potential energy converts to thermal energy when burned to power an engine.

The First Law of Thermodynamics

• The first law states the conservation of energy within thermodynamic systems, where the change in internal energy equals heat added minus work done.
• ΔU = Q – W, where ΔU is the change in internal energy, Q is the heat added, and W is the work done.
• Internal energy includes the total kinetic and potential energies of molecules in the system.
• Heat is energy transfer due to temperature difference; work is energy transfer via displacement caused by a force.
• Energy within a thermodynamic system isn't created or destroyed, only converted.
• Adding heat increases internal energy, raising temperature or changing phase. When the system does work, it decreases internal energy, lowering temperature or expanding volume.
• For a gas in a cylinder with a piston, adding heat increases internal energy and expanding the gas causes it to do work, reducing its internal energy.

The Second Law of Thermodynamics

• Entropy, a measure of system disorder, increases in isolated systems or remains constant ideally, but never decreases.
• Natural processes proceed towards increasing universal disorder.
• ΔS ≥ 0, is how it is mathematically expressed where ΔS represents the change in entropy of the system.
• Energy conversions are never perfectly efficient, with energy lost to heat from friction or turbulence.
• Heat represents energy degradation, being less available for useful work. Entropy increase is tied to dissipating energy.
• Heat engines convert thermal energy into work, but cannot convert all thermal energy; some gets exhausted as waste heat.

The Third Law of Thermodynamics

• Focuses on systems' behavior at absolute zero (0 K or -273.15°C)
• As temperature approaches absolute zero, entropy approaches a minimum or zero value; perfectly ordered systems have zero entropy.
• Reaching absolute zero in a finite number of steps is practically impossible.
• As a system approaches absolute zero, the energy to remove each heat increment increases.
• At absolute zero, molecular motion stops, and the system is in its lowest energy state.
• Systems tend to evolve to states of minimum energy and maximum order.
• At absolute zero, particles arrange perfectly in a crystalline structure.
• Sustaining absolute zero is impossible due to inevitable interactions that introduce energy and disorder.
• Understanding behaviors at extremely low temperatures such as superconductivity and superfluidity is important.

Energy Transfer, Efficiency and Management

• In medical imaging, energy transfer from device to patient and back to the detector is important.
• Maximize energy efficiency ensuring minimal energy to achieve diagnostic or therapeutic goals in medical devices.
• Effective energy management involves monitoring and controlling energy use within safe limits.
• Understanding the balance between energy input and output is crucial for safe and effective medical applications.

Applications in Diagnostic Imaging

• Diagnostic imaging relies heavily on energy conservation for high-quality images with minimized patient risk.
• Techniques like X-ray, CT, and MRI use various energy forms, the conservation, and transfer is essential.
• In X-ray imaging, a controlled amount of X-ray energy is directed towards the patient, and the energy interacts with tissues.
• Energy conservation ensures the right amount of energy is used for clear images without unnecessary radiation.
• A balance between energy input and output is important for image quality and patient safety.
• MRI uses radiofrequency energy to excite hydrogen nuclei, and the released energy is converted into images.
• Efficient energy transfer is important for high-resolution images and energy conservation helps in optimizing the imaging process.

Therapeutic Applications

• Energy conservation is important in medical physics, especially radiation therapy.
• Delivering radiation to treat cancer involves precise energy management maximizing therapeutic effect minimizing damage to surrounding healthy tissues.
• Calculate and control the energy delivered to the tumor carefully.
• The energy absorbed by tumor cells must induce cell death while minimizing energy absorbed by healthy tissues.
• Aspects of energy conservation in radiation therapy:
  • Accurate dose calculations
  • Treatment planning systems
  • Constant monitoring of energy delivery