University Physics Volume 1

# Key Terms

### Key Terms

dynamics
study of how forces affect the motion of objects and systems
external force
force acting on an object or system that originates outside of the object or system
force
push or pull on an object with a specific magnitude and direction; can be represented by vectors or expressed as a multiple of a standard force
free fall
situation in which the only force acting on an object is gravity
free-body diagram
sketch showing all external forces acting on an object or system; the system is represented by a single isolated point, and the forces are represented by vectors extending outward from that point
Hooke’s law
in a spring, a restoring force proportional to and in the opposite direction of the imposed displacement
inertia
ability of an object to resist changes in its motion
inertial reference frame
reference frame moving at constant velocity relative to an inertial frame is also inertial; a reference frame accelerating relative to an inertial frame is not inertial
law of inertia
see Newton’s first law of motion
net external force
vector sum of all external forces acting on an object or system; causes a mass to accelerate
newton
SI unit of force; 1 N is the force needed to accelerate an object with a mass of 1 kg at a rate of $1m/s21m/s2$
Newton’s first law of motion
body at rest remains at rest or, if in motion, remains in motion at constant velocity unless acted on by a net external force; also known as the law of inertia
Newton’s second law of motion
acceleration of a system is directly proportional to and in the same direction as the net external force acting on the system and is inversely proportional to its mass
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 it exerts
normal force
force supporting the weight of an object, or a load, that is perpendicular to the surface of contact between the load and its support; the surface applies this force to an object to support the weight of the object
tension
pulling force that acts along a stretched flexible connector, such as a rope or cable
thrust
reaction force that pushes a body forward in response to a backward force
weight
force $w→w→$ due to gravity acting on an object of mass m