# Conservation Laws - Key terms

### CONSERVATION LAWS:

A set of principles describing physical properties that remain constant—that is, are conserved—throughout the various processes that occur in the physical world. The most significant of these laws concerns the conservation of energy (as well as, with qualifications, the conservation of mass); conservation of linear momentum; conservation of angular momentum; and conservation of electrical charge.

### CONSERVATION OF ANGULAR MOMENTUM:

A physical law stating that when the sum of the external torques acting on a physical system is equal to zero, the total angular momentum of the system remains unchanged. Angular momentum is the momentum of an object in rotational motion, and torque is a force applied around an axis of rotation.

### CONSERVATION OF ELECTRICALCHARGE:

A physical law which holds that for an isolated system, the net electrical charge is constant.

### CONSERVATION OF ENERGY:

A law of physics stating that within a system isolated from all other outside factors, the total amount of energy remains the same, though transformations of energy from one form to another take place.

### CONSERVATION OF LINEAR MOMENTUM:

A physical law stating that when the sum of the external force vectorsacting on a physical system is equal to zero, the total linear momentum of the system remains unchanged—or is conserved.

### CONSERVATION OF MASS:

A physical principle stating that total mass is constant, and is unaffected by factors such asposition, velocity, or temperature, in any system that does not exchange any matter with its environment. Unlike the other conservation laws, however, conservation of mass is not universally applicable, but applies only at speeds significant lower than that of light—186,000 mi (297,600 km) per second. Close to the speed of light, mass begins converting to energy.

### CONSERVE:

In physics, "to conserve" something means "to result in no net loss of" that particular component. It is possible that within a given system, the component may change form or position, but as long as the net value of the component remains the same, it has been conserved.

### FRICTION:

The force that resists motion when the surface of one object comes into contact with the surface of another.

### MOMENTUM:

A property that a moving body possesses by virtue of its mass and velocity, which determines the amount of force and time required to stop it.

### SYSTEM:

In physics, the term "system" usually refers to any set of physical interactions isolated from the rest of the universe. Anything outside of the system, including all factors and forces irrelevant to a discussion of that system, is known as the environment.