- acceleration
- the rate at which an object’s velocity changes over a period of time

- carrier particle
- a fundamental particle of nature that is surrounded by a characteristic force field; photons are carrier particles of the electromagnetic force

- dynamics
- the study of how forces affect the motion of objects and systems

- external force
- a force acting on an object or system that originates outside of the object or system

- 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

- force field
- a region in which a test particle will experience a force

- free-body diagram
- a sketch showing all of the external forces acting on an object or system; the system is represented by a dot, and the forces are represented by vectors extending outward from the dot

- free-fall
- a situation in which the only force acting on an object is the force due to gravity

- friction
- a force past each other of objects that are touching; examples include rough surfaces and air resistance

- inertia
- the tendency of an object to remain at rest or remain in motion

- inertial frame of reference
- a coordinate system that is not accelerating; all forces acting in an inertial frame of reference are real forces, as opposed to fictitious forces that are observed due to an accelerating frame of reference

- law of inertia
- see Newton’s first law of motion

- mass
- the quantity of matter in a substance; measured in kilograms

- net external force
- the vector sum of all external forces acting on an object or system; causes a mass to accelerate

- Newton’s first law of motion
- a body at rest remains at rest, or, if in motion, remains in motion at a constant velocity unless acted on by a net external force; also known as the law of inertia

- Newton’s second law of motion
- the net external force ${\mathbf{\text{F}}}_{\text{net}}$ on an object with mass $m$ is proportional to and in the same direction as the acceleration of the object, $\mathbf{\text{a}}$, and inversely proportional to the mass; defined mathematically as $\mathbf{\text{a}}=\frac{{\mathbf{\text{F}}}_{\text{net}}}{m}$

- Newton’s third law of motion
- whenever one body exerts a force on a second body, the first body experiences a force that is equal in magnitude and opposite in direction to the force that the first body exerts

- normal force
- the force that a surface applies to an object to support the weight of the object; acts perpendicular to the surface on which the object rests

- system
- defined by the boundaries of an object or collection of objects being observed; all forces originating from outside of the system are considered external forces

- tension
- the pulling force that acts along a medium, especially a stretched flexible connector, such as a rope or cable; when a rope supports the weight of an object, the force on the object due to the rope is called a tension force

- thrust
- a reaction force that pushes a body forward in response to a backward force; rockets, airplanes, and cars are pushed forward by a thrust reaction force

- weight
- the force $\mathbf{\text{w}}$due to gravity acting on an object of mass $m$; defined mathematically as:
*$\mathbf{\text{w}}=m\mathbf{\text{g}}$*, where $\mathbf{\text{g}}$ is the magnitude and direction of the acceleration due to gravity