Forces and Newton's Laws of Motion

Comprehensive vocabulary flashcards covering key definitions, units, equations, and principles from the lecture on Forces and Newton's Laws of Motion.

Mechanics

The branch of physics that deals with the motion of objects and the forces that change this motion.

Kinematics

The branch of mechanics that describes the motion of objects without regard to the forces causing it.

Dynamics

The branch of mechanics that considers the forces that affect the motion of moving objects and systems (the causes of motion).

Force

A push or pull acting on an object that possesses both magnitude and direction, capable of causing or changing its motion.

Newton ($\text{N}$)

The standard metric (SI) unit of force; one Newton is the amount of force required to give a $1\,\text{kg}$ mass an acceleration of $1\,\text{m/s}^2$ ($1\,\text{N} = 1\,\text{kg} \cdot \text{m/s}^2$).

Free-Body Diagram

A vector diagram representing all external forces acting upon an object, where each force is depicted as an arrow pointing in the direction of the force with a length reflective of its magnitude.

Balanced Forces

Forces acting on an object that are equal in magnitude and opposite in direction, canceling each other out so that no net or unbalanced force acts upon the object.

Unbalanced Forces

Forces acting on an object that do not cancel out completely, producing a non-zero net force that changes the object's state of motion.

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

The total vector sum obtained by combining all individual forces acting upon an object.

External Force

A force that acts on an object or system of interest from the outside.

Internal Force

A force that acts between two objects or particles that are both within the designated system (acting from within).

Net External Force

The total combined external force acting upon an entire system from the outside.

Tension (Internal Deformation)

An internal structural force that acts by pulling the particles of an object apart, causing elongation.

Compression (Internal Deformation)

An internal structural force that acts by pressing the particles of an object together.

Shearing (Internal Deformation)

An internal force that causes ripping or tearing of an object when forces pull or push across parallel planes in opposite directions.

Torsion (Internal Deformation)

An internal force resulting in the internal twisting of an object caused by twisting forces.

Contact Force

A force that can cause or change the motion of an object through direct physical contact between interacting bodies.

Action-at-a-Distance Force

A non-contact force that results even when two interacting objects are separated by space and not in physical contact (such as gravitational, electrical, or magnetic forces).

Applied Force ($F_{\text{app}}$)

A force that is applied directly to an object by a person or another object.

Normal Force ($F_{\text{norm}}$ or $N$)

The support force exerted upon an object by a stable surface in contact with it, directed perpendicular to the surface.

Friction Force ($F_{\text{frict}}$)

The contact force exerted by a surface as an object moves or attempts to move across it, acting opposite to the direction of motion.

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

A special type of frictional force acting on objects traveling through air that opposes their motion, most notable at high speeds or for large surface areas.

Tension Force ($F_{\text{tens}}$ or $T$)

The pulling force transmitted through a flexible connector (such as a string, rope, cable, or wire) when pulled tight from opposite ends, acting parallel to its length.

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

The restoring force exerted by a compressed or stretched spring that acts to return an object to its equilibrium position, proportional to the stretch or compression.

Mass

A measure of the quantity of matter in an object, determined by the number and types of atoms it contains; measured in kilograms ($\text{kg}$) and remaining constant regardless of location in the universe.

Weight ($W$ or $F_{\text{grav}}$)

The force of gravity acting on an object, calculated by $W = m \times g$, which varies depending on location and the gravitational field strength.

Gravitational Field Strength ($g$)

The acceleration due to gravity acting on a mass at a given location, approximately equal to $9.8\,\text{N/kg}$ (or $9.81\,\text{m/s}^2$) on Earth's surface and $1.7\,\text{N/kg}$ on the Moon.

Sliding Friction

The friction force that opposes motion when an object actively slides across a surface, calculated by $F_{\text{frict-sliding}} = \mu_{\text{frict-sliding}} \times F_{\text{norm}}$.

Static Friction

The friction force that opposes the initiation of motion when two surfaces are at rest relative to one another, satisfying $F_{\text{frict-static}} \le \mu_{\text{frict-static}} \times F_{\text{norm}}$.

Coefficient of Friction ($\mu$)

A dimensionless constant representing the resistance to sliding between two contact surfaces, dependent primarily upon the physical nature of the materials in contact.

Newton’s First Law of Motion

The fundamental law stating that a body at rest tends to remain at rest, and a body in motion tends to remain in motion at a constant velocity unless acted upon by a net external force.

Inertia

The natural tendency of an object to resist changes in its state of motion (to remain at rest or keep moving at a constant speed in a straight line), which is directly proportional to its mass.

System

One or more objects selected for physical analysis to determine which forces are external and must be evaluated, and which are internal and can be ignored.

Newton’s Second Law of Motion

The physical law stating that net external force causes acceleration, mathematically formulated as $F_{\text{net}} = m \times a$.

Directly Proportional

A mathematical relationship between two variables such that multiplying or dividing one variable by a factor causes the other variable to be multiplied or divided by the identical factor (e.g., $a \propto F_{\text{net}}$).

Inversely Proportional

A mathematical relationship where multiplying one variable by a factor causes the other variable to be divided by that same factor (e.g., $a \propto \frac{1}{m}$).

Newton’s Third Law of Motion

The physical law stating that whenever a first object exerts a force on a second object, the first object experiences a force equal in magnitude but opposite in direction to the force it exerts.

Action-Reaction Pairs

Simultaneous, equal, and oppositely directed forces that occur whenever two objects interact, which do not cancel each other out because they act on separate systems.

Thrust

A forward reaction force produced in response to the backward expulsion of matter (such as exhaust gas from a rocket) at high velocity.