Overview
This lecture covers various forms of energy, including kinetic, potential, and other special types, explaining their physical significance, formulas, and how energy can be transformed or stored.
Kinetic Energy
- Kinetic energy is the energy of motion, present in any moving object.
- Kinetic energy is proportional to the object's mass and the square of its speed.
- Rotational kinetic energy applies to objects spinning about an axis.
Potential Energy
- Potential energy is stored energy due to an object's position or state.
- Gravitational potential energy depends on mass, gravity, and height (PE = mgh).
- Objects higher above ground have more gravitational potential energy.
- Moving an object opposite to gravity increases its potential energy; moving with gravity decreases it.
Electric Potential Energy
- Electric potential energy arises from the positions of charges in an electric field.
- Electric potential energy increases when a charge is moved against the electric force.
- Formula: Electric PE = -qEy (analogous to gravitational PE).
Elastic Potential Energy
- Elastic potential energy is stored in stretched or compressed springs.
- Formula: PE = (1/2)kx², where k is the spring constant and x is displacement.
- Greater compression or stretching increases stored energy.
Chemical Potential Energy
- Chemical potential energy is stored in chemical bonds, as in batteries or food.
- Released during chemical reactions, powering devices or living organisms.
Phase Change and Pressure-Related Potential Energy
- During phase changes (e.g., freezing, condensation), energy is released without temperature change.
- In solids, molecules closer together after freezing release energy; evaporation absorbs energy.
- Pressurized gases have high potential energy and do work when released to lower pressure.
Energy Flow & Gradients
- Energy flows from high to low: height, pressure, electric potential, or temperature.
- Heat flows from hot to cold; electric current flows from high to low voltage.
Thermal Energy
- Thermal energy in solids is vibrational movement of atoms; in gases, it's particle speed.
- For gases: Average kinetic energy = (3/2)kT; root mean square velocity relates to temperature and molar mass.
Sound and Light Energy
- Sound is a pressure wave transferring energy through a medium (not through a vacuum).
- Light is an electromagnetic wave, carrying energy and exhibiting both wave and particle properties (photons).
- Light is part of the electromagnetic spectrum; higher frequency waves (gamma rays) have more energy.
Mechanical Energy
- Mechanical energy is the sum of kinetic and potential energy in a system.
Key Terms & Definitions
- Kinetic Energy — energy due to motion; KE = ½mv².
- Potential Energy — stored energy based on position or state.
- Gravitational Potential Energy — energy due to position in a gravitational field; PE = mgh.
- Electric Potential Energy — energy from location in an electric field; PE = -qEy.
- Elastic Potential Energy — energy stored in deformed springs; PE = ½kx².
- Chemical Potential Energy — energy stored in chemical bonds.
- Thermal Energy — energy from molecular motion.
- Sound Wave — a pressure wave that transfers energy through a medium.
- Electromagnetic Wave — a wave of oscillating electric and magnetic fields (e.g., light).
- Mechanical Energy — total energy from both kinetic and potential energy.
Action Items / Next Steps
- Review and memorize formulas for different types of potential and kinetic energy.
- Practice problems involving energy transformations (kinetic to potential, elastic, etc.).
- Read about energy flow in real-world systems (batteries, engines, and electricity).