Glossary
Average Power
The total work done or energy transferred divided by the total time taken to perform that work or transfer that energy.
Example:
If a construction crane lifts a beam over a period of 30 seconds, its average power output is the total work done divided by those 30 seconds.
Closed System
A system where no matter or energy is exchanged with its surroundings, meaning the total energy within the system remains constant.
Example:
A perfectly insulated thermos containing hot coffee approximates a closed system, as heat energy is prevented from escaping.
Conservation of Energy
A fundamental principle stating that the total energy of an isolated system remains constant, though it can transform from one form to another.
Example:
In a frictionless pendulum swing, the total mechanical energy (kinetic + potential) remains constant, demonstrating the conservation of energy.
Conservative Forces
Forces for which the work done on an object is independent of the path taken, such as gravity and spring forces.
Example:
The work done by conservative forces like gravity on a roller coaster only depends on the initial and final heights, not the twists and turns of the track.
Elastic Potential Energy (U_s)
Energy stored in a deformable object, like a spring, when it is stretched or compressed from its equilibrium position.
Example:
A compressed spring in a toy dart gun holds elastic potential energy ready to propel the dart.
Energy Transformation
The process by which energy changes from one form to another, such as potential energy converting to kinetic energy.
Example:
A hydroelectric dam exemplifies energy transformation, converting the gravitational potential energy of water into kinetic energy, then into electrical energy.
Gravitational Potential Energy (U_g)
Energy stored in an object due to its height above a reference point, determined by its mass, gravity, and height.
Example:
A diver standing on a high platform possesses considerable gravitational potential energy before jumping.
Instantaneous Power
The power at a specific moment in time, calculated as the product of the force applied and the instantaneous velocity of the object.
Example:
As a rocket launches, its instantaneous power output continuously increases as its velocity and engine thrust change over time.
Kinetic Energy (KE)
The energy an object possesses due to its motion. It depends on both the object's mass and its speed.
Example:
A bowling ball rolling down the lane has significant kinetic energy due to its mass and velocity.
Non-Conservative Forces
Forces for which the work done on an object depends on the path taken, typically dissipating mechanical energy as heat or sound, like friction or air resistance.
Example:
The non-conservative force of air resistance causes a falling skydiver to eventually reach a terminal velocity, converting mechanical energy into thermal energy.
Potential Energy
Stored energy an object possesses due to its position or configuration, which can be converted into other forms of energy.
Example:
A stretched rubber band stores potential energy that can be released to launch a small projectile.
Power
The rate at which work is done or energy is transferred, indicating how quickly energy is being used or converted.
Example:
A high-performance sports car has high power because its engine can do a large amount of work (accelerate the car) in a very short time.
Work
Work is done when a force causes a displacement. It is positive if the force and displacement are in the same direction, negative if opposite, and zero if perpendicular.
Example:
Lifting a weight straight up involves positive work against gravity, while holding it stationary does no work.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy, representing the energy transfer in motion.
Example:
When a car accelerates, the net work done by the engine and road forces directly increases the car's kinetic energy.