Spectroscopy

A set of three physical laws forming the basis of classical mechanics. The first law (inertia) states an object remains at rest or in uniform motion unless acted upon by a net external force. The second law quantifies force as mass times acceleration, \(\vec{F} = m\vec{a}\). The third law states that for every action, there is an equal and opposite reaction.

A Newtonian fluid's shear stress is directly proportional to the rate of shear strain. This linear relationship is defined by Newton's law of viscosity: \(\tau = \mu \frac{du}{dy}\), where \(\tau\) is the shear stress, \(\mu\) is the dynamic viscosity (a constant of proportionality), and \(\frac{du}{dy}\) is the shear rate or velocity gradient.

Bernoulli's principle states that for an inviscid flow, an increase in a fluid's speed occurs simultaneously with a decrease in pressure or a decrease in its potential energy. It is a statement of the conservation of energy for a moving fluid, commonly expressed as \(p + \frac{1}{2}\rho v^2 + \rho gh = \text{constant}\) along a streamline.

Fluid mechanics is the branch of applied mechanics concerned with the statics (fluids at rest) and dynamics (fluids in motion) of liquids and gases. It applies fundamental principles of mass, momentum, and energy conservation to analyze and predict fluid behavior. Its applications are vast, ranging from aerodynamics and hydraulics to meteorology and oceanography.

Centrifugal force is an inertial or "fictitious" force that appears to act on a mass when viewed in a rotating reference frame. It is directed radially outward from the axis of rotation. This force is not a fundamental interaction but arises from the inertia of the object, its tendency to maintain motion in a straight line in an inertial frame.

Generalized Hooke's Law is the constitutive equation for linear elastic materials, stating that the stress tensor is linearly proportional to the strain tensor. The relationship is expressed as \(\sigma = C : \varepsilon\), where \(\sigma\) is the stress tensor, \(\varepsilon\) is the strain tensor, and \(C\) is the fourth-order stiffness tensor containing the material's elastic constants.

This law states that every particle attracts every other particle in the universe with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. The formula is \(F = G \frac{m_1 m_2}{r^2}\), where \(G\) is the gravitational constant. It unified terrestrial and celestial mechanics.

In an isolated system, the total momentum remains constant. An isolated system is one not subject to external forces. This principle follows from Newton's laws of motion. For a system of particles, the total momentum \(\vec{p}_{\text{total}} = \sum_{i} m_i \vec{v}_i\) is conserved if the net external force is zero. This is fundamental to analyzing collisions.

In a reference frame rotating with an angular velocity \(\boldsymbol{\omega}\), the centrifugal force \(\mathbf{F}_{\mathrm{cf}}\) acting on an object of mass \(m\) at a position vector \(\mathbf{r}\) from the origin is given by the vector formula: \(\mathbf{F}_{\mathrm{cf}} = -m \boldsymbol{\omega} \times (\boldsymbol{\omega} \times \mathbf{r})\). This formula shows the force is directed perpendicular to the axis of rotation and outwards.