"Until now we have analyzed motions of objects without considering the forces causing them. Here we relate cause and effect: by drawing the free-body diagram of an object to identify the forces acting on it, we can use Newton's second law to determine its acceleration. Once the acceleration is known, we can determine its velocity and position by the methods developed in Chapter 2." p99

CENTER OF MASS

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

INERTIA
A PROPERTY OF A BODY THAT RESISTS ANY CHANGE IN MOTION. FOR TRANSLATION MOTION, MASS IS A MEASURE OF THE BODY INERTIA. IT IS HARD TO CHANGE THE STATE OF MOTION OF A HIGH MASS OBJECT. FOR ROTATION, THE MOMENT OF INERTIA OF A BODY IS A MEASURE OF BODY INERTIA.

LINEAR
PROPERTY OF SYSTEMS WHERE THE SYSTEM OUTPUT OR RESPONSE IS IN DIRECT PROPORTION TO THE INPUT. DOUBLING THE INPUT (LOAD, FORCE, ENERGY, TENSION,...) HAS THE EFFECT OF DOUBLING THE OUTPUT (STRETCH, COMPRESSION, DISPLACEMENT,...)

LINEAR MOMENTUM
THIS IS A PRODUCT OF THE MASS AND VELOCITY OF A BODY (M*V) WHICH IS CONSERVED (PRESERVED) IN COLLISIONS AND INTERACTIONS AS LONG AS THE EXTERNALLY APPLIED FORCE ON THE SYSTEM IS ZERO.

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.