Understanding Forces and Motion: Newton's Laws and Beyond

Force and Material Response

Force: Any cause altering a body's rest or motion, or causing strain.

Materials respond to forces:

• Hard: Resist shape changes under force.
• Elastic: Regain shape after force removal.
• Plastic: Permanently deform under force.

Elastic deformation: Force (F) is proportional to elongation (Δl): F = K * Δl

Force Characteristics

• Magnitude: Numerical value (Newtons).
• Direction: Line of action.
• Sense: Vector's arrowhead.
• Application Point: Location of force on the body.

Force Systems

Force System: Forces acting simultaneously. Each is a component.

Net Force: Single force equivalent to all forces, producing the same effect.

Newton's Laws of Motion

First Law: Inertia

A body remains at rest or in uniform motion unless acted upon by a net force.

Inertia: Tendency to maintain rest or motion.

Second Law: Acceleration

Acceleration is proportional to the net force, in the same direction, and inversely proportional to mass.

Third Law: Action-Reaction

Interacting bodies exert equal and opposite forces on each other, acting on different bodies.

Other Forces and Concepts

Weight

Earth's gravitational attraction on a body.

Friction

Opposes motion at the interface of two bodies, moving or tending to move.

Uniform Circular Motion (UCM)

Motion in a circle with constant speed, covering equal arcs in equal times.

Models of the Universe

Geocentric Model

Earth-centered universe (Aristotle, Ptolemy).

Heliocentric Model

Sun-centered universe (Aristarchus, Copernicus, Galileo).

Kepler's Laws of Planetary Motion

1. Planets move in elliptical orbits with the Sun at one focus.
2. A line from the Sun to a planet sweeps equal areas in equal times.
3. The square of a planet's orbital period is proportional to the cube of its orbit's radius.

Universal Gravitation

All bodies attract each other with a force proportional to their masses' product and inversely proportional to the square of the distance between them.

This explains:

• Falling objects and weight
• Satellite motion
• Comet motion
• Tides