Glossary
Closed System
A system where no matter or energy can enter or leave, ensuring that the total energy within it remains constant.
Example:
A perfectly insulated thermos containing hot coffee approximates a closed system where heat energy is conserved within the coffee.
Conservation of Energy
A fundamental principle stating that energy cannot be created or destroyed, only transformed from one form to another or transferred between systems.
Example:
When a roller coaster goes down a hill, its potential energy is converted into kinetic energy, but the total energy remains constant (ignoring friction).
Conservative Forces
Forces for which the work done on an object moving between two points is independent of the path taken, and depends only on the initial and final positions.
Example:
Gravity is a conservative force because the work done lifting an object depends only on the height difference, not the path.
Conservative Forces
Forces for which the work done is independent of the path taken, depending only on the initial and final positions, and allowing for the definition of a potential energy function.
Example:
Gravity is a conservative force because the work done by gravity on an object moving from one height to another is the same regardless of the path it takes.
Conservative forces
Forces for which the work done on an object moving between two points is independent of the path taken. These forces allow for the interconversion of kinetic and potential energy without loss of mechanical energy.
Example:
Gravity is a conservative force because the work done by gravity on an object moving from one height to another is the same, regardless of the path it takes.
Elastic Potential Energy (PEe)
The potential energy stored in an elastic material, such as a spring, when it is stretched or compressed from its equilibrium position.
Example:
A stretched slingshot band stores elastic potential energy ready to propel a projectile.
Energy Bar Charts
Visual representations used to track the transformation and transfer of energy within a system, showing initial and final energy states.
Example:
Drawing energy bar charts for a block sliding down a ramp helps visualize how gravitational potential energy converts into kinetic energy and thermal energy due to friction.
Energy conservation
A fundamental principle stating that energy can change forms but is never created or destroyed within an isolated system. It describes how energy transforms and moves.
Example:
When a ball is thrown upwards, its initial kinetic energy is gradually converted into gravitational potential energy, demonstrating energy conservation as the total energy remains constant (ignoring air resistance).
Gravitational Potential Energy (PEg)
The potential energy an object possesses due to its position in a gravitational field, dependent on its mass, height, and the acceleration due to gravity.
Example:
A book resting on a high shelf has gravitational potential energy that would convert to kinetic energy if it fell.
Gravitational Potential Energy (PEg)
The potential energy an object possesses due to its position in a gravitational field. It depends on the object's mass, the acceleration due to gravity, and its height.
Example:
A book resting on a high shelf has gravitational potential energy that would be converted to kinetic energy if it fell.
Gravitational Potential Energy (Ug)
The potential energy an object possesses due to its position in a gravitational field, dependent on its mass, height, and the acceleration due to gravity.
Example:
A rock perched on the edge of a cliff has high gravitational potential energy, which converts to kinetic energy if it falls.
Kinetic Energy (K)
The energy an object possesses due to its motion, directly proportional to its mass and the square of its velocity.
Example:
A baseball thrown at high speed has significant kinetic energy, which allows it to break a window upon impact.
Kinetic Energy (KE)
The energy an object possesses due to its motion, directly proportional to its mass and the square of its velocity.
Example:
A fast-moving baseball has significant kinetic energy that allows it to break a window upon impact.
Kinetic energy (KE)
The energy an object possesses due to its motion. It depends on the object's mass and velocity.
Example:
A car speeding down a highway has significant kinetic energy, which is directly related to its mass and the square of its speed.
Law of Conservation of Energy
States that in a closed system, the total energy remains constant. Energy can transform from one form to another, but it cannot be created or destroyed.
Example:
When a roller coaster car descends a hill, its gravitational potential energy is converted into kinetic energy, but the total mechanical energy remains constant if friction is negligible.
Mechanical Energy (ME)
The sum of a system's kinetic energy and potential energy, representing the total energy associated with motion and position.
Example:
In a swinging pendulum, the total mechanical energy remains constant, continuously converting between kinetic and potential forms.
Mechanical Energy (ME)
The sum of an object's or system's kinetic energy and potential energy. In the absence of non-conservative forces, mechanical energy is conserved.
Example:
As a diver falls from a platform, their mechanical energy (sum of kinetic and gravitational potential energy) remains constant if air resistance is ignored.
Mechanical Energy (ME)
The sum of an object's kinetic energy and potential energy within a system.
Example:
For a swinging pendulum, its mechanical energy is the sum of its kinetic energy at the bottom of the swing and its gravitational potential energy at the highest point.
Negative Work
Work done on a system when the force applied has a component opposite to the direction of the displacement, decreasing the system's energy.
Example:
Friction does negative work on a sliding object, converting its kinetic energy into thermal energy and slowing it down.
Non-conservative forces
Forces for which the work done on an object moving between two points depends on the path taken. These forces typically dissipate mechanical energy, often converting it into thermal energy.
Example:
Friction is a non-conservative force because the work it does on a sliding object depends on the distance the object slides, converting mechanical energy into heat.
Nonconservative Forces
Forces for which the work done on an object moving between two points depends on the path taken, often dissipating mechanical energy as other forms like heat or sound.
Example:
Air resistance is a nonconservative force that causes a falling object to eventually reach terminal velocity, as mechanical energy is lost to the environment.
Nonconservative Forces
Forces for which the work done depends on the path taken, leading to a change in the total mechanical energy of a system.
Example:
When a car brakes, nonconservative forces like friction between the tires and the road convert the car's kinetic energy into heat and sound.
Positive Work
Work done on a system when the force applied has a component in the direction of the displacement, increasing the system's energy.
Example:
When a person lifts a weight, they do positive work on the weight, increasing its gravitational potential energy.
Potential Energy (PE)
Stored energy an object possesses due to its position, configuration, or state, with the capacity to do work.
Example:
A stretched bowstring holds potential energy that is released to propel an arrow forward.
Potential Energy (U)
Stored energy an object possesses due to its position or configuration, with different forms depending on the force involved.
Example:
A stretched rubber band stores potential energy that can be released to launch a small projectile.
Potential energy (PE)
Stored energy an object possesses due to its position or configuration. It can be converted into kinetic energy.
Example:
A stretched bowstring stores potential energy that is released as kinetic energy when an arrow is fired.
Reversible Shape Changes
Changes in an object's form that store potential energy and can be undone, returning the object to its original shape and releasing the stored energy.
Example:
Compressing a spring involves a reversible shape change, storing elastic potential energy that can then launch an object.
Spring Potential Energy (PEs)
The potential energy stored in an elastic spring when it is compressed or stretched from its equilibrium position. It depends on the spring constant and the displacement.
Example:
A toy dart gun stores spring potential energy when its spring is compressed, which is then released to propel the dart.
Spring Potential Energy (Us)
The potential energy stored in an elastic spring when it is compressed or stretched from its equilibrium position.
Example:
A toy dart gun uses a compressed spring to store spring potential energy, which is then converted into the dart's kinetic energy.
System
A defined collection of objects or particles chosen for analysis in a physics problem. Clearly defining the system is crucial for applying conservation laws.
Example:
When analyzing a block sliding down a ramp, you might define the system as just the block, or as the block and the Earth, depending on whether you want to consider gravitational potential energy as internal or external work.
System Boundaries
The imaginary line or surface that separates the objects or region of interest (the system) from its surroundings.
Example:
When analyzing a ball thrown upwards, defining the ball and Earth as the system boundaries allows for the conservation of mechanical energy.
Thermal Energy
The internal energy of a system associated with the random motion of its atoms and molecules, often generated by friction or other nonconservative forces.
Example:
Rubbing your hands together quickly generates thermal energy, making them feel warm.
Thermal energy
The internal energy of a system associated with the random motion of its atoms and molecules. It is often produced when mechanical energy is dissipated by non-conservative forces like friction.
Example:
When you rub your hands together, the work done against friction converts mechanical energy into thermal energy, making your hands feel warm.
Work
The transfer of energy to or from a system by means of a force acting over a displacement.
Example:
Pushing a heavy box across a room requires work to be done, transferring energy to the box.
Work
The transfer of energy to or from a system by means of a force acting over a displacement. It is a scalar quantity and can be positive (energy added) or negative (energy removed).
Example:
When you push a heavy box across the floor, you are doing work on the box, transferring energy to it.
Work (by nonconservative forces)
The energy transferred into or out of a system by a nonconservative force, causing a change in the system's total mechanical energy.
Example:
The work done by friction on a sliding block reduces its kinetic energy, converting it into thermal energy.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy.
Example:
If a car accelerates, the Work-Energy Theorem explains that the net work done by the engine and other forces equals the increase in the car's kinetic energy.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy. It provides a direct link between work and motion.
Example:
If a car's engine does positive work on it, the car's kinetic energy increases, which is explained by the Work-Energy Theorem.
Work-Energy Theorem
States that the net work done on an object equals the change in its kinetic energy, or more broadly, the work done by nonconservative forces equals the change in mechanical energy.
Example:
If a car accelerates, the net work-energy theorem states that the work done by the engine (minus friction) directly increases the car's kinetic energy.