Fundamentals of Kinematics and Forces in Physics

Item 1. Kinematics and Reference Systems

Referral System

A reference system is a point or set of points we use to determine if a body moves. If a moving body changes its position with respect to the reference as time passes, it is moving; if it does not change its position, it is at rest.

Path and Displacement

• Path: The path (e.g., Path A) describes the trajectory of the object on its way; that is, the set of points through which it passes in its movement.
• Displacement: A vector that originates at the starting point of the movement and ends at the final point of movement.

Speed and Velocity

• Speed: The magnitude of displacement per unit time. It is measured in m/s.
• Instantaneous Speed: The speed value at any given moment, often measured in a speedometer.
• Average Speed: Calculated by dividing the total space traveled between the time taken.

Uniform Rectilinear Motion (MRU)

MRU occurs when there are no changes in direction; the path must be straight, and the object should always maintain the same direction and value for velocity.

Acceleration

Acceleration is the magnitude measuring how a mobile object's speed varies per unit time. It is measured in m/s².

Uniformly Accelerated Rectilinear Motion (MRUA)

MRUA is movement whose trajectory is a straight line and whose acceleration is constant.

Radius Angle

Radius Angle is an angle inscribed in a circle which defines an arc with a length equal to the radius of the circle. It is the measure where angles are typically measured in SI units.

Item 2. Forces

Definition of Force

Force is any cause capable of causing a deformation or a change in the state of motion of a body.

Elasticity and Measurement

• Hooke's Law: States that when a force is applied to a spring, it causes a deformation proportional to the magnitude of the force.
• Dynamometers: A device used to measure forces. It contains a calibrated spring so that by exerting a force or hanging a weight, the indicator marks the value of the force.

Concurrent Forces

Concurrent forces are those whose directions intersect at some point; non-concurrent forces are parallel.

Principles of Dynamics (Newton's Laws)

Principle of Inertia

If a body moving suffers no external disruption, it continues to move forever with uniform rectilinear motion.

First Dynamic Principle

When the net force acting on a body is zero, the body maintains its state of motion: if it was at rest, it continues at rest; if it was in motion, it continues moving with MRU.

Second Dynamic Principle

When a force acts on a body, it causes an acceleration in the same direction as the force, such that $F = ma$. If there is more than one force, $F_{net} = ma$.

Third Dynamic Principle

When one body exerts a force called an action on another, the latter responds with an equal and opposite reaction force.

A Newton is the force acting on a body of 1 kg that imparts an acceleration of 1 m/s².

Frictional Force

Frictional force is the force that always opposes the motion.