Basics of Physics - II

(The Article is intended to academic purpose)

Newtonian Mechanics: The velocity of an object can change when the object is acted on by one or more forces from other objects. Newtonian Mechanics relates acceleration and forces.

Force: Forces are vector quantities. Their magnitude are defined in terms of the acceleration they would give the standard kilogram. A force that accelerates standard body by exactly 1 m/s² is defined to have a magnitude of 1 N. The direction of a force is the direction of the acceleration it causes. Forces are combined according to rules of vector algebra. The net force on a body is the vector sum of all the forces acting on the body.

Newton’s First Law: If there is no net force on a body, the body remains at rest if initially at rest or moves in a straight line at constant speed if it is in motion.

Inertial Frame of Reference: Reference Frame in which Newtonian mechanics holds are called inertial frame of reference. Reference Frames in which Newtonian mechanics doesn’t hold are called non-inertial reference frame or non inertial frames.

Mass: The mass of a body is the characteristic of that body that relates the body’s acceleration to the net force causing the acceleration. Masses are scalar quantities.

Newton’s second law: The net force F on body with mass m is related to body’s acceleration by the relation F=ma. Or in other words time rate change of momentum is directly proportional to applied net force on the body.

Free Body Diagram (FBD): FBD is a stripped down diagram in which only one body is considered. That body is represented by either a sketch or a dot. The external forces on the body are drawn, and a coordinated system is superimposed, oriented so as to simplify the solution.

Gravitational Force: A gravitational force on a body is a pull by another body. For Earth the force is directed toward the ground which is assumed to be an inertial frame.

Weight: The weight of the body is the magnitude of the upward force needed to balance the gravitational force on a body.

Normal Force: A normal force is the force on a body from the surface against which the body presses. The normal force is always perpendicular to the surface.

Frictional force: A frictional force on a body when the body slides or attempts to slide along a surface. The force is always parallel to the surface and directed so as to oppose the sliding. On a frictionless surface, the frictional force is negligible.

Newton’s Third Law: As per Newton’s third law there is equal and opposite reaction to the applied force.

Friction: When a force tends to slide a body along a surface, a frictional force from the surface acts on the body. The frictional force is parallel to the surface and directed so as to oppose the sliding. It is due to the bonding between the body and the surface. If the body doesn’t slide, the frictional force is static frictional force. If there is a sliding, the frictional force is kinetic frictional force.

Drag force: When there is a relative motion between air and a body, the body experiences a drag force. That opposes the relative motion and points in the direction in which the fluid flows relative to the body.

Terminal Speed: When a blunt object has fallen far enough through air, the magnitude of the drag force and the gravitational force become equal. Then the body falls at constant speed called as terminal speed.

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