Overview
The lecture introduces the concept of energy, focusing on its definition, types, and how energy changes through work, particularly emphasizing potential energy and its relationship to conservative forces like gravity.
Defining Energy
- Energy is a property that an object possesses and can be changed or transferred.
- There is no simple, short definition for energy; it is a foundational yet subtle concept in physics.
- Work is the process by which the energy of an object is changed.
Work and Energy Transfer
- Work is done when a force moves an object over a distance (force × distance).
- The work you do can change an object's motion or its position relative to a force like gravity.
Types of Energy
- Energy is categorized into kinetic energy (energy of motion) and potential energy (energy due to position).
Potential Energy
- Potential energy is energy stored due to the position of an object.
- Gravitational potential energy is the most common example; energy increases with height.
- Other examples include elastic (bowstring), electrical, and magnetic potential energy.
- Potential energy does not require the object to be moving.
Gravitational Potential Energy
- Gravitational potential energy (PE) is defined as PE = mgh (mass × gravitational acceleration × height).
- Gravity only does work on an object when it moves vertically (not horizontally).
- When an object is raised, gravity does negative work; when lowered, gravity does positive work.
- Total work done by gravity over a closed path (up and down) is zero, indicating gravity is a conservative force.
Conservative and Non-Conservative Forces
- Conservative forces (like gravity) result in zero total work over a closed path.
- Non-conservative forces (like friction) always do negative work, regardless of direction, and never add to zero.
Key Terms & Definitions
- Energy — A property an object possesses that allows it to do work or be changed by work.
- Work — The process of energy transfer via force acting over a distance (W = F × d).
- Potential Energy (PE) — Stored energy due to an object's position, especially relative to a force.
- Kinetic Energy — Energy an object possesses due to its motion.
- Conservative Force — A force for which the total work over any closed path is zero (e.g., gravity).
- Non-Conservative Force — A force that always dissipates energy, and total work is not zero (e.g., friction).
Action Items / Next Steps
- Review the definition and examples of potential and kinetic energy.
- Prepare to dive deeper into gravitational potential energy in the next session.