Newton's Laws of Motion and Related Concepts

Newton’s Laws of Motion

• Newton’s First Law: Every object remains at rest or in uniform motion unless acted upon by a net external force (law of inertia).

• Inertial Reference Frame: Valid if Newton's First Law holds; examples include a stationary observer or one moving at constant velocity.

Concepts of Force and Mass

• Force: A vector quantity involving a push or pull; causes changes in motion.

• Mass: Quantity of matter (kg); measures inertia. Weight varies by location; weight = mass x gravity.

Newton’s Second Law

• Formula: (net force equals mass times acceleration).

• Acceleration: Directly proportional to net force and inversely proportional to mass.

• Force is measured in Newtons (N), where .

Newton’s Third Law

• For every action, there is an equal and opposite reaction; forces act on different objects, not the same one.

• Forces are described using subscripts for clarity regarding which object they act on.

Weight and Normal Force

• Weight is the force of gravity on an object (near Earth, weight varies with location).

• Normal Force: Counteracts weight, acts perpendicular to the surface; equals weight when no other vertical forces exist.

Free-Body Diagrams

• Key for visualizing forces on an object:

  • Draw the object.

  • Label forces acting on it.

  • Accurately represent magnitudes and directions.

Tension

• A force that occurs when a string pulls on an object, neglecting the string’s mass.

Inclines

• Define a new x-y coordinate system along and perpendicular to the incline to analyze forces.

• Weight components on an incline:

  • Parallel:

  • Perpendicular:

Applications and Examples

• Analyze problems involving Newton’s Laws in different contexts (inclines, tension in cables, free-body diagrams).