Weak interaction

Weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature, along with strong interaction, electromagnetic force, and gravitation. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons. Its most familiar effect is beta decay (or the emission of electrons by neutrons or positrons by protons in atomic nuclei) and the associated radioactivity. It is a non-contact force, called weak because the typical field strength is 10⁻¹¹ times the strength of the electromagnetic force and some 10⁻¹³ times that of the strong force, when forces are compared between particles interacting in more than one way.


The weak force was originally (in the 1930s) described by Fermi's theory of a contact four-fermion interaction, that is to say, a "force" without range.


http://en.wikipedia.org/wiki/Weak_nuclear_force

Weak acid

A weak acid is an acid that dissociates incompletely. It does not release all of its hydrogens in a solution, donating only a partial amount of its protons to the solution. These acids have higher pKa than strong acids, which release all of their hydrogen atoms when dissolved in water.
Examples of weak acids include acetic acid (CH₃COOH) and oxalic acid (H₂C₂O₄).

Dissociation

Weak acids ionize in water solution to only a moderate extent; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissociated HA still remains. Weak acids in water dissociate as:

The equilibrium concentrations of reactants and products are related by the acid dissociation constant expression, (K_a):

The greater the value of K_a, the more the formation of H⁺ is favored, and the lower the pH of the solution. The K_a of weak acids varies between 1.8×10^-16 and 55.5. Acids with a K_a less than 1.8×10^-16 are weaker acids than water.

Corrosivity

While strong acids are generally assumed to be the most corrosive, this is not always true. The carborane superacid (H(CHB₁₁Cl₁₁), which is one million times stronger than sulfuric acid, is entirely non-corrosive, whereas the weak acid hydrofluoric acid (HF) is extremely corrosive and can dissolve, among other things, glass and all metals except iridium.


http://en.wikipedia.org/wiki/Weak_acid

Rebound hardness

Rebound hardness, also known as dynamic hardness, measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity. The device used to take this measurement is known as a scleroscope.

Two scales that measures rebound hardness are the Leeb rebound hardness test and Bennett hardness scale.


http://en.wikipedia.org/wiki/Scratch_hardness#Scratch_hardness

Indentation hardness

Indentation hardness measures the resistance of a sample to permanent plastic deformation due to a constant compression load from a sharp object; they are primarily used in engineering and metallurgy fields. The tests work on the basic premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are Rockwell, Vickers, and Brinell 

http://en.wikipedia.org/wiki/Scratch_hardness#Scratch_hardness

Scratch hardness

Scratch hardness is the measure of how resistant a sample is to fracture or plastic (permanent) deformation due to friction from a sharp object. The principle is that an object made of a hard material will scratch an object made of a softer material. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer

http://en.wikipedia.org/wiki/Scratch_hardness#Scratch_hardness

Hardness Conversion Tables

There are three main types of hardness measurements: scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another.

http://en.wikipedia.org/wiki/Scratch_hardness#Scratch_hardness