Law of Conservation of Energy

Energy when considered in all its forms, is automatically conserved. The total amount of energy remains numerically constant in time (although some of energy may swap from one form to other).

Whenever one object exerts a force on another object - either a pull or push. Physics can introduce a Potential Energy (or other form of energy) such that a Law of Conservation of Energy holds.

This is ofcourse, a remarkable property of nature, not just a sign of Physicists ingenuity.

What is Fluid?

Substances capable of flowing are fluids. They don't have their own shape and they take shape of containing vessel. Fluid undergoes shear deformation continuously till force acts on it.

Liquid is a incompressible fluid as they are difficult to compress for practical purpose so they have definite volume. Gas is a compressible fluid. Their volume varies with temperature & pressure.

If we talk of ideal fluid then that fluid should not have Viscosity, Surface Tension and compressibility. But in nature all fluids have one or all properties depending on condition so they are called real or practical fluids. Hence they pose certain amount of resistance when set in motion.

Differences between Ionic, Covalent, Metallic & Vanderwall Bonds

What are Hydrogen Bonds?

This bond may be considered as a special type of dipole bond, but it is one that is considerably stronger. It occurs between molecules in which one end is a hydrogen atom. When a hydrogen atom is covalent bonded  to a relatively large atom such as Nitrogen, Oxygen or Fluorine a powerful permanent dipole is set up.

This is because the electron cloud tends to become concentrated around that part of molecule containing the Nitrogen, Oxygen and Fluorine Nucleus, thus leaving the positively charged Hydrogen Nucleus relatively unprotected.  

Consequently a strong permanent dipole is created that can bond to other similar dipoles with a force near that involved in the ionic bond.

 A good example of Hydrogen bond is water molecule.