Dynamics is the study of how forces affect the motion of objects and systems A free-body diagram is a drawing of all external forces acting on a body

Newton’s first law states that a body at rest remains at rest or, if moving, remains in motion in a straight line at a constant speed, unless acted on by a net external force. External forces are any forces outside of a body that act on the body.

force — a push or pull on an object with a specific magnitude and direction; can be represented by vectors; can be expressed as a multiple of a standard force; the SI unit of force is…. system — one or more objects of interest for which only the forces acting on them from the outside are considered, but not the forces acting between them or inside them. inertia — the tendency of an object at rest to remain at rest, or for a moving object to remain in motion in a straight line and at a constant speed. law of inertia — Newton’s first law of motion: a body at rest remains at rest or, if in motion, remains in motion at a constant speed in a straight line, unless acted on by a net external force….