Glossary
Closed System
A system that exchanges energy but not matter with its surroundings. The total energy within this system remains constant if no external work is done.
Example:
A sealed thermos containing hot coffee is a good approximation of a closed system, as it exchanges heat (energy) with the outside but not coffee (matter).
Conservation of Energy
The principle that the total energy of an isolated system remains constant over time, meaning energy cannot be created or destroyed, only transformed from one form to another.
Example:
When a roller coaster car glides down a hill, its gravitational potential energy is converted into kinetic energy, demonstrating the principle of energy conservation.
External Force
A force exerted on a system by something outside the system.
Example:
The force of friction acting on a sliding block is an external force if the block is defined as the system.
Internal Force
A force exerted by one part of a system on another part within the same system.
Example:
The tension in the rope connecting two blocks in a multi-block system is an internal force if both blocks are part of the defined system.
Isolated System
A system that exchanges neither matter nor energy with its surroundings, meaning its total energy remains constant.
Example:
The entire universe is often considered an isolated system for the purpose of energy conservation discussions.
Kinetic Energy
The energy an object possesses due to its motion. It depends on the object's mass and speed.
Example:
A baseball thrown at high speed has significant kinetic energy, which is why it can break a window upon impact.
Law of Conservation of Energy
A fundamental law of physics stating that energy in a closed system is neither created nor destroyed, but rather transformed from one form to another.
Example:
The transformation of chemical energy in a battery into electrical energy to power a device is an application of the Law of Conservation of Energy.
Negative Work
Work done by a system that decreases its total energy, occurring when the force and displacement are in opposite directions.
Example:
When a car brakes, friction does negative work on the car, reducing its kinetic energy and bringing it to a stop.
Open System
A system that exchanges both matter and energy with its surroundings.
Example:
A boiling pot of water on a stove is an open system because it loses both heat (energy) and steam (matter) to the air.
Positive Work
Work done on a system that increases its total energy, occurring when the force and displacement are in the same general direction.
Example:
When you lift a weight, the force you apply is upwards, and the displacement is upwards, resulting in positive work done on the weight.
Potential Energy
The energy an object possesses due to its position or configuration. Common types include gravitational potential energy and elastic potential energy.
Example:
A stretched spring or a book held high above the ground both store potential energy that can be converted into other forms.
Power
The rate at which work is done or energy is transferred. It is calculated as work divided by time.
Example:
A powerful engine can accelerate a car very quickly because it can deliver a high amount of power, doing a lot of work in a short time.
System
A defined object or collection of objects chosen for analysis, separated from its surroundings.
Example:
When analyzing the motion of a pendulum, you might define the pendulum bob and the string as your system.
Thermal Energy
The internal energy of a system due to the random motion of its atoms and molecules. It is often associated with heat.
Example:
Rubbing your hands together quickly generates thermal energy, making them feel warm.
Work
The transfer of energy that occurs when a force causes a displacement of an object in the direction of the force.
Example:
Pushing a heavy box across a room requires you to do work on the box, transferring energy to it.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy.
Example:
If you calculate the total work done by all forces on a moving car, the Work-Energy Theorem tells you that this value will equal the change in the car's kinetic energy.