"The dynamics of single particles or a small number of particles were discussed in Chapters 1-3. It is important to consider a group of particles as a system and study the dynamics of that system. Initially, the system of particles will consist of a constant number of particles, and the equations for the system will be developed. In the last part of this chapter, particles will leave or enter the system so that the total mass of the system will vary with its dynamics. Problems of this nature occur in rocket propulsion systems, where fue particles are discharged from each system. These systems will be variable mass systems, and the center of mass will vary with the dynamics." p269

ARBITRARY
OF AN UNSPECIFIED NATURE, UNDETERMINED, UNKNOWN

ARBITRARY PARTICLES
PARTICLES IN ANY POSITION WITH ANY MASS, VELOCITIES,...

CENTER OF MASS

CENTER OF MASS
A POINT WHERE THE MASS OF AN OBJECT SEEMS TO BE CONCENTRATED

CONTROL VOLUME
SYSTEMS MAY BE IMAGINED AS POSITIONED WITHIN AN IMAGINARY CONTAINER (THE "CONTROL VOLUME") SO THAT RESOURCES WHICH FLOW IN AS WELL AS OUT CAN BE ACCURATELY TABULATED.

FORCE
A PUSH OR A PULL

FORCE

INTERNAL
WITHIN A SYSTEM

INTERNAL FORCES
FORCES THAT ARE EXERTED BETWEEN PARTS OF THE SYSTEM

MASS
THE RESISTANCE OF AN OBJECT TO A CHANGE IN TRANSLATIONAL MOTION

MOMENT
A FORCE APPLIED TO AN OBJECT AT SOME DISTANCE FROM THE ROTATION AXIS THAT MAY CAUSE THE OBJECT TO ROTATE. THIS IS THE SAME AS A TORQUE. THE MOMENT IS CALCULATED AS THE PRODUCT OF A FORCE TIMES THE DIRSTANCE OF ITS POINT OF APPLICATION FROM THE AXIS OF ROTATION.

PARTICLE
AN OBJECT WITH VERY SMALL DIMENSIONS COMPARED TO ANY OTHER SYSTEM PARAMETER. ONE CAN THINK OF A PARTICLE AS LOCATED AT A POINT IN SPACE AND IGNORE ANY EFFECTS CAUSED BY THE FINITE SIZE OF THE OBJECT.

VOLUME