Physics Unit 3: Forces and Newton's Laws

Vocabulary practice flashcards covering forces, Newton's first law, free body diagrams, force types, net force, and terminal velocity.

Force ($\vec{F}$)

A push or pull exerted on an object. It is a vector quantity, which means it possesses both magnitude and direction.

Newton ($\text{N}$)

The standard unit of force, defined as the amount of force required to give a $1\,\text{kg}$ mass an acceleration of $1\,\text{m/s}^2$.

Inertia

The tendency of an object to resist changes in its motion. It depends directly on mass, meaning objects with more mass have more inertia and are more difficult to move or stop.

Newton's First Law (The Law of Inertia)

The principle stating that an object at rest stays at rest, and an object in motion stays in motion at a constant velocity, unless acted on by an unbalanced force.

Balanced Forces

Forces acting on an object that are equal in magnitude and opposite in direction, canceling each other out ($F_{\text{net}} = 0$), or a condition where no forces act on the object at all. Balanced forces result in constant velocity or remaining at rest.

Unbalanced Forces

Forces acting on an object where opposing forces are not equal and do not cancel out, creating a non-zero net force that causes the object to accelerate (speed up, slow down, or change direction).

Net Force ($F_{\text{net}}$)

The vector sum of all forces acting on an object; it represents what is left over after all opposing forces have canceled.

Free Body Diagram

A diagram used to document all forces acting on an object, where all force arrows point away from the object and their lengths correspond to force magnitudes. Free body diagrams do not indicate the direction of the object's motion.

Applied Force ($F_a$)

A push or pull applied to an object by a person or another object, excluding forces exerted specifically by a rope or a spring.

Gravitational Force / Weight ($F_g$ or $F_{\text{grav}}$)

A non-contact field force due to gravitational attraction between two objects, present whenever an object is on or near Earth or another massive body.

Normal Force ($F_N$)

The contact force exerted perpendicularly by a surface onto an object resting or pressing against that surface.

Friction Force ($F_f$)

A contact force that resists sliding motion when two surfaces slide against each other, acting in the direction opposite to the motion.

Air Resistance ($F_{\text{air}}$)

A special type of frictional force that acts against objects as they travel through air, increasing in magnitude as the object's velocity increases.

Tension Force ($F_T$)

The pull exerted on an object through a string, rope, or cable. When tension force is identified, applied force is not selected.

Spring Force ($F_{\text{sp}}$)

The push or pull exerted on an object by a compressed or stretched spring or elastic material. When spring force is identified, applied force is not selected.

Terminal Velocity

The constant maximum velocity reached by a falling object when the upward force due to air resistance equals the downward force of gravity (weight). For a human, this is approximately $125\,\text{miles/hour}$.

Net Force Direction (Speeding Up)

The condition where the net force is directed in the exact same direction as the object's motion.

Net Force Direction (Slowing Down)

The condition where the net force is directed in the opposite direction of the object's motion.

Scientific Law

A statement based on repeated observations of phenomena that appear to happen everywhere in the universe, describing what happens without explaining why.

Three Effects of an Unbalanced Net Force

The three possible changes in motion when net force is non-zero: speeding up, slowing down, or changing direction.