Glossary
Isolated System
A system where no external forces do work on it, meaning no energy is added to or removed from the system from outside its boundaries.
Example:
A ball falling freely in a vacuum is an isolated system with the Earth, as no air resistance or other external forces act upon it.
Joule (J)
The SI unit of energy and work, representing the amount of energy transferred when a force of one newton acts over a distance of one meter.
Example:
Lifting a 1 kg apple by 1 meter requires approximately 9.8 Joules of work.
Kinetic Energy (K)
The energy an object possesses due to its motion, calculated as $K = \frac{1}{2}mv^2$.
Example:
A fast-moving baseball has a large amount of Kinetic Energy, which is why it can do significant work when it hits something.
Law of Conservation of Energy
States that the total energy of an isolated system remains constant; energy can change forms (kinetic, potential, thermal) but is never created or destroyed.
Example:
When a roller coaster car glides down a hill, its gravitational potential energy transforms into kinetic energy, but the total energy of the car-Earth system stays the same due to the Law of Conservation of Energy if friction is ignored.
Potential Energy (U)
Stored energy an object possesses due to its position or configuration, such as gravitational potential energy ($U_g = mgh$) or elastic potential energy ($U_s = \frac{1}{2}kx^2$).
Example:
A stretched bowstring stores Potential Energy, which is then converted into kinetic energy of the arrow when released.
Power
The rate at which work is done or energy is transferred, indicating how quickly energy is used or converted.
Example:
A powerful sports car has high Power because its engine can do a large amount of work (accelerate the car) in a very short amount of time.
Total Mechanical Energy (TME)
The sum of an object's potential energy (U) and kinetic energy (K), which remains constant in a closed system with no non-conservative forces acting.
Example:
As a pendulum swings, its Total Mechanical Energy remains constant, with energy continuously converting between kinetic energy at the bottom and potential energy at the top of its swing.
Watt (W)
The SI unit of power, equivalent to one joule per second (J/s), representing the rate of energy transfer or work done.
Example:
A 60-Watt light bulb consumes 60 joules of electrical energy every second it is on.
Work (W)
The transfer of energy to or from an object by means of a force acting over a displacement, calculated as $W = Fd \cos heta$.
Example:
When you push a heavy box across the floor, you are doing Work on the box, transferring energy to it.
Work-Energy Principle
States that the net work done on an object equals its change in kinetic energy, quantifying how energy transfer affects an object's motion.
Example:
If a car's engine does positive work on it, the car's kinetic energy increases, causing it to speed up, as described by the Work-Energy Principle.