Newton's Laws of Motion, Forces, and Dynamics

Vocabulary practice flashcards covering Newton's three laws of motion, contact and field forces, normal and tension forces, friction, Hooke's law, inertial and noninertial frames, and free-body diagrams.

Force

A push or pull that one body exerts on another; an interaction that is an action rather than a property of an object, represented as a vector quantity having magnitude and direction, measured in newtons ($1\,\text{N} = 1\,\text{kg}\cdot\text{m/s}^2$).

Contact Forces and Field Forces

Contact forces result from the physical touching and microscopic interactions of two bodies (such as tension, normal force, and friction), whereas field forces act across empty space without physical contact (such as gravitational, electrical, and magnetic forces).

Newton's First Law of Motion

The law of inertia stating that an object at rest remains at rest, and an object in motion continues in motion with the same speed and in the same direction, as long as no net external force acts on it.

Inertia

The intrinsic tendency of an object to resist any attempt to change its velocity.

Net Force

The vector sum of all individual external forces acting on an object, determined geometrically by lining up vectors head-to-tail or algebraically by resolving and summing components along coordinate axes.

Newton's Second Law of Motion

The law stating that the acceleration of an object is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object, expressed as $\vec{F}_{\text{net}} = m\vec{a}$.

Newton's Third Law of Motion

The principle stating that forces always occur in matched interaction pairs; if object A exerts a force on object B, then object B exerts a force of equal magnitude and opposite direction of the same type on object A ($\vec{F}_{AB} = -\vec{F}_{BA}$).

Normal Force ($\vec{N}$)

The supporting contact force exerted perpendicular to the surface of contact between an object and its support; on a flat horizontal surface its magnitude is $N = mg$, whereas on an incline of angle $\theta$ it is given by $N = mg\cos(\theta)$.

Tension ($\vec{T}$)

A pulling force transmitted along the length of a flexible connector (such as a string, rope, chain, wire, cable, or tendon) that acts strictly parallel to the connector's length and pulls outward at both ends.

Tension from a Perpendicular Force

The magnified pulling force established in a flexible connector when a perpendicular load ($F_\perp$) acts at its center, given by the expression $T = \frac{F_\perp}{2\sin(\theta)}$, where $\theta$ is the angle the deflected connector makes with the straight line.

Friction ($\vec{f}$)

A resistive contact force that opposes relative motion or the tendency toward motion between contacting surfaces, acting parallel to the surface interface.

Static Friction ($f_s$)

The resistive force that opposes the initiation of motion between two surfaces at rest relative to each other, with a magnitude satisfying $f_s \le \mu_s N$, where $\mu_s$ is the coefficient of static friction.

Kinetic Friction ($f_k$)

The resistive force that opposes relative motion between surfaces sliding past each other, having magnitude $f_k = \mu_k N$, where $\mu_k$ is the coefficient of kinetic friction (typically less than $\mu_s$).

Hooke's Law

The physical law stating that a stretched or compressed spring exerts a restoring force that is directly proportional to its displacement from the relaxed position and directed in the opposite sense: $\vec{F}_{\text{restore}} = -k\Delta\vec{x}$.

Spring Constant ($k$)

The constant of proportionality in Hooke's law that quantifies the stiffness of a spring.

Real Force

A force that has an identifiable physical origin (such as gravity or contact interactions) and has a genuine Newton's third law reaction force partner.

Fictitious Force

An apparent force that arises purely because an observer is in an accelerating or noninertial reference frame (such as a rotating or decelerating frame), characterized by the absence of a physical origin or reaction partner.

Inertial Frame of Reference

A reference frame that does not accelerate or rotate relative to a known inertial frame, within which all observed forces are real and Newton's laws of motion hold in their standard form.

Coriolis Effect

The apparent deflection of moving bodies (such as air in weather systems or ocean currents) when viewed from a rotating frame of reference like the spin of Earth.

Free-Body Diagram (FBD)

A physics diagram that isolates an object of interest, represents it as a point or box, and depicts all external forces acting directly on that object as vector arrows pointing away from it.

Apparent Weight

The normal force supporting an object in a vertical accelerating system (such as an elevator); it is greater than the gravitational weight ($N > mg$) when accelerating upward, equal to gravitational weight ($N = mg$) at constant velocity, and less than gravitational weight ($N < mg$) when accelerating downward.