Conceptual Physics: Forces and Newton's Laws of Motion

Vocabulary practice flashcards covering forces, contact and field forces, Newton's first and third laws of motion, mass versus weight, friction, and action/reaction pairs.

Force

Any push or pull on an object in a particular direction, resulting from an interaction between two objects.

Vector Quantity

A quantity, such as force or weight, for which the direction in which it acts matters.

Contact Forces

Forces that occur when two interacting objects physically touch, including applied forces, friction, tension, spring/elastic forces, support/normal forces, and buoyant forces.

Field Forces

Forces that can act through space without physical contact, including gravity, electromagnetic forces, the strong nuclear force, and the weak nuclear force.

Newton ($\text{N}$)

The SI unit of force; one Newton is equal to approximately $\frac{1}{4}$ of a pound.

Newton's First Law of Motion

The law stating that an object in motion or at rest will remain in motion or at rest unless acted upon by an outside, unbalanced force; also known as the Law of Inertia.

Inertia

An object's ability to resist a change in motion, specifically in speed or direction.

Kilogram ($\text{kg}$)

The SI unit of mass.

Mass

The stuff that makes up an object; a scalar quantity measured in kilograms ($\text{kg}$) that does not change regardless of location in the Universe.

Weight

The force on an object due to the pull of gravity; a vector quantity measured in Newtons ($\text{N}$) that changes based on gravitational pull.

Acceleration Due to Gravity ($g$)

The rate of downward gravitational acceleration, equal to $9.8\,\text{m/s}^2$ on Earth, used to calculate force in Newtons by multiplying with mass in kilograms.

Free-body Diagram

A picture representing all of the forces acting on an isolated object using arrows to represent force vectors.

Friction

A contact force that always acts in a direction opposing an object's motion, occurring between two objects in contact.

Normal Force ($F_{norm}$)

The support force supplied by the surface upon which an object rests, acting upward on the object.

Coefficient of Friction ($\mu$)

A value (pronounced mu) describing the roughness of surfaces in contact, used in the formula $F_{fric} = \mu F_{norm}$.

Static Coefficient of Friction ($\mu_{\text{static}}$\text{)}

The coefficient of friction for stationary objects, which is always higher than the kinetic coefficient of friction.

Kinetic Coefficient of Friction ($\mu_{\text{kinetic}}$\text{)}

The coefficient of friction for moving objects, which is always lower than the static coefficient of friction.

Air Resistance

A frictional force opposing the motion of an object through air that is responsible for the terminal velocity of a falling object.

Newton's Third Law of Motion

The law stating that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

Action/Reaction Force Pairs

Equal and opposite force pairs resulting from an interaction between two objects, always involving two different objects (Object A on Object B, and Object B on Object A).

Force Cancellation Condition

The requirement that forces must act on the same object to cancel out, meaning action/reaction pairs cannot cancel because they act on two different objects.

The Horse and Cart Problem

A demonstration of Newton's third law showing that motion occurs because the ground exerts a forward reaction force on the horse's hooves (ground on hoof), allowing the system to move forward.