Physics Dynamics, Friction, Circular Motion & Gravity: Modules 2, 5–6

acceleration

the rate at which an object's velocity changes over a period of time

dynamics

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

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

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

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 F(net) on an object with mass m is proportional to and in the same direction as the acceleration of the object, a, and inversely proportional to the mass; defined mathematically as: a = F(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

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

weight

the force w due to gravity acting on an object of mass m; defined mathematically as: w=mg, where g is the magnitude and direction of the acceleration due to gravity.

friction

a force that opposes relative motion or attempts at motion between objects in contact

Hooke's law

proportional relationship between the force F on a material and the deformation ΔL it causes, F = kΔL.

kinetic friction

a force that opposes the motion of two systems that are in contact and moving relative to one another

magnitude of kinetic friction

fk=μkN, where μk is the coefficient of kinetic friction

magnitude of static friction

fs ≤ μs N, where μs is the coefficient of static friction and N is the magnitude of the normal force

static friction

a force that opposes the motion of two systems that are in contact and are not moving relative to one another

strain

ratio of change in length to original length

stress

ratio of force to area

angular velocity

ω, the rate of change of the angle with which an object moves on a circular path

arc length

Δs, the distance traveled by an object along a circular path

center of mass

the point where the entire mass of an object can be thought to be concentrated

centrifugal force

a fictitious force that tends to throw an object off when the object is rotating in a non-inertial frame of reference

centripetal acceleration

the acceleration of an object moving in a circle, directed toward the center

centripetal force

any net force causing uniform circular motion

gravitational constant, G

a proportionality factor used in the equation for Newton's universal law of gravitation; it is a universal constant—that is, it is thought to be the same everywhere in the universe

Newton's universal law of gravitation

every particle in the universe attracts every other particle with a force along a line joining them; the force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

non-inertial frame of reference

an accelerated frame of reference

radians

a unit of angle measurement

radius of curvature

radius of a circular path

rotation angle

the ratio of the arc length to the radius of curvature on a circular path: Δθ=Δs/r

uniform circular motion

the motion of an object in a circular path at constant speed