**Newton's First Law**

**An object at rest tends to stay at rest and an
object in motion tends to stay in motion with the same speed and in the
same direction unless acted upon by an unbalanced force. This is known
as the **__law of inertia__.

**Newton's Second Law**

**A force 'F' acting on a body gives it an
acceleration 'a' which is in the direction of the force and has
magnitude inversely proportional to the mass 'm' of the body: **

**F = ma**

**Newton's Third Law**

**Whenever a body exerts a force on another body, the
latter exerts a force of equal magnitude and opposite direction on the
former. This is known as the **__weak law of action and reaction__.

**Strong Law of Action and
Reaction**

**For every action force, there is a corresponding
reaction force which is equal in magnitude and opposite in direction.
Furthermore, the forces are central forces, i.e., they act along the
line joining the particles.**

**Wave-Particle Duality**

**Microparticles, electrons, protons, photons, atoms
and so forth, propagate as if they were waves, and exchange energy as if
they were particles. That's the Wave-Particle duality.**

**Quantum Randomness**

**It appears that identical particles in identical
situations need not to behave identically. That is the essence of
quantum randomness.**

**Conservation of Energy**

**If the forces acting on a particle are conservative
so that there exists a function V(r) such that**

**F = -
Ñ V(r)**

**then the total energy**

**E = K + U**

**given as the sum of kinetic energy (often
defined informally as energy of motion) and potential energy (often
defined informally as energy at rest) is a constant.**

**The First Law of
Thermodynamics**

**The first law of thermodynamics is a consequence of
conservation of energy and requires that a system may exchange energy
with the surroundings strictly by heat flow or work. Therefore, for
change in energy dE, heat change , work done dW,**

**dE = dQ - dW**

**The Second Law of
Thermodynamics**

**The second law of thermodynamics prohibits the
construction of a perpetual motion machine "of the second kind." There
are two usual statements of this law. Kelvin's formulation states that
it is impossible for a system operating in a cycle and in contact with
one thermal reservoir to perform positive work in the surroundings.
Clausius's formulation states that it is impossible for a system
operating in a cycle to produce positive heat flow from a colder body to
a hotter body.**

Two important consequences of the second law are the existence of a new
state variable, the entropy S, and the theorem

**dQ
£ T dS**

where dQ is the heat change, dT is the temperature change, and dS is the
change in entropy.

**The Third Law of
Thermodynamics**

**As temperature goes to 0, the entropy S approaches
a constant . Furthermore, it guarantees that the entropy of a pure,
perfectly crystalline substance is 0 if the absolute temperature is 0.**

**Zeroth Law of Thermodynamics**

**If two systems are in thermal equilibrium with a
third system, then they must be in thermal equilibrium with each other.**

**Uncertainty Principle**

**A quantum mechanical principle due to Werner
Heisenberg (1927) that, in its most common form, states that it is not
possible to simultaneously determine the position and momentum of a
particle. Moreover, the better position is known, the less well the
momentum is known (and vice versa). The principle is sometimes known as
the Heisenberg uncertainty principle, and can be stated exactly as**

**
Dx Dpx
= h/2p**

where Dx is
the uncertainty in position,
Dpx
is the uncertainty in momentum, and h in h/2p
is Planck's constant; h = 6.6262 *
10^{-34}
[J s].