Overview
This lecture explains the different forms of energy, how they relate to kinetic and potential energy, and how energy transforms between forms according to the first law of thermodynamics.
Forms of Energy
- Energy exists in thermal, chemical, electric, radiant, nuclear, magnetic, elastic, sound, mechanical, luminous, and mass forms.
- Thermal energy comes from the random motion of microscopic particles (e.g., warm water).
- Chemical energy is stored in the arrangement of atoms and molecules (e.g., food).
- Electric energy is due to electric potential among charges (e.g., in a capacitor).
- Radiant energy is electromagnetic radiation, such as light.
- Nuclear energy is released during nuclear reactions like fusion and fission (e.g., nuclear plants).
- Magnetic energy is related to electric energy (e.g., MRI superconducting magnets).
- Elastic energy is stored when materials are stretched or compressed (e.g., stretched rubber band).
- Sound energy is produced by vibrations in matter (e.g., vocal cords).
- Mechanical energy is the sum of kinetic and potential energy of an object (e.g., pendulum).
- Luminous energy is visible light (e.g., flashlight beam).
- Mass can be converted to energy (E=mc²), as in nuclear explosions.
Kinetic and Potential Energy
- All energy forms are either kinetic, potential, or a combination.
- Some forms of energy (e.g., luminous and radiant) can overlap.
Energy Transformations and the First Law of Thermodynamics
- Energy transformation occurs when energy changes from one form to another.
- The first law of thermodynamics states energy can only change if added or removed from a system.
- Energy seems to be lost in a system but is actually transformed to another form.
- Devices that convert energy from one form to another are called transducers.
- Efficiency is the ratio of useful output to input energy in a transformation.
- Some processes approach 100% efficiency (e.g., pendulum in a vacuum), while others are much lower (wind turbine max 59%, photosynthesis 6%).
Key Terms & Definitions
- fusion — Nuclear reaction where nuclei combine to form a heavier nucleus, releasing energy.
- electromagnetic radiation — Energy made of oscillating electric and magnetic fields, moving through space as photons.
- fission — Splitting a nucleus into smaller parts, releasing energy.
- pendulum — Body swinging from a fixed point due to gravity, used in timing devices.
- first law of thermodynamics — Change in a system’s energy equals heat added minus work done by the system.
- potential energy — Stored energy due to position, condition, or rest mass.
- kinetic energy — Energy due to an object’s motion, equal to ½ mass × velocity².
Action Items / Next Steps
- Review the differences and examples of each energy form.
- Study the concept of energy transformation and efficiency.
- Read about the first law of thermodynamics in your textbook.