Force, Motion, and Newton's Laws Explained

Understanding Force, Motion, and Newton's Laws

Force and Motion

Every action force is able to alter the state of movement or rest of bodies, or produce in them some deformation. A vector is a directed line segment.

Elements of the force vector:

• Point of application: The point on which force is applied.
• Magnitude: The intensity of the force.
• Direction: The line on which the force vector acts.
• Sense: Indicates which of the two possible orientations of force is adopted.

Types of Forces

Weight of a body: Gravitational traction force exerted by the Earth.

Power system: A set of forces acting on a body, equivalent to a single imaginary force.

Resultant force: The force on a body that produces the same effect as the set of all the forces acting; the vector sum of the forces of the system.

Decomposition of forces: Forces which together produce over a field the same effect as the original force.

Two or more forces applied to the same body are in equilibrium when their effects cancel each other, that is, when the resultant force is zero.

Normal force: Force that holds the support surface of a body on it.

Friction force: Force that appears on the surface of contact bodies, opposing the movement of these.

Newton's Laws of Motion

1st Law: Law of Inertia

A body remains in its state of rest or uniform rectilinear motion if no force acts upon it, or if the resultant of the forces acting is zero.

2nd Law: Fundamental Law of Dynamics

If a resultant force acts on a body, it acquires an acceleration directly proportional to the applied force, the body's mass being the proportionality constant.

3rd Law: Law of Action and Reaction

If one body exerts a force, which we call action, over another body, this, in turn, exerts a force on the first one, which we call reaction, with the same magnitude and direction, but in the opposite sense.

Characteristics of action and reaction forces:

• They are simultaneous: One force reacts to the other, but both forces act simultaneously.
• They act on different bodies: These forces are opposite but do not cancel each other, as each applies to a different body. Therefore, they can produce significant effects on the bodies.
• Sometimes some of these forces are not seen: Occasionally, one of the bodies is not accelerated because it has a large mass or because there are other major forces opposing the motion.

Inertia

Inertia is the property of matter that makes it unable to change its state of rest or motion by itself.