# Mechanical properties of solids (summary)

Mechanical properties of solids are the properties that determine how solids respond to external forces. These properties include:

·         Elasticity: Elasticity is the ability of a solid to regain its original shape and size after being deformed by an external force.

·         Plasticity: Plasticity is the ability of a solid to undergo permanent deformation without breaking.

·         Strength: Strength is the ability of a solid to resist deformation or breakage.

·         Hardness: Hardness is the ability of a solid to resist scratching or indentation.

·         Toughness: Toughness is the ability of a solid to absorb energy without breaking.

Elasticity

When an external force is applied to a solid, the atoms in the solid are displaced from their original positions. If the force is small enough, the atoms will return to their original positions when the force is removed. This property is called elasticity.

The elasticity of a solid is measured by its elastic modulus. The elastic modulus is a measure of how much the solid deforms in response to a given force. There are three types of elastic modulus:

·         Young's modulus: Young's modulus measures the resistance of a solid to longitudinal deformation, such as stretching or compressing.

·         Shear modulus: Shear modulus measures the resistance of a solid to transverse deformation, such as twisting or bending.

·         Bulk modulus: Bulk modulus measures the resistance of a solid to uniform compression or expansion.

Plasticity

If the force applied to a solid is large enough, the atoms in the solid will not be able to return to their original positions when the force is removed. This type of deformation is called plastic deformation.

Plasticity is a desirable property for many materials. For example, metals are often plastically deformed to create new shapes and sizes.

Strength

The strength of a solid is its ability to resist deformation or breakage. The strength of a solid depends on its elastic modulus, its plasticity, and its other mechanical properties.

There are two types of strength:-

·         Yield strength: Yield strength is the stress at which a solid begins to undergo plastic deformation.

·         Ultimate strength: Ultimate strength is the maximum stress that a solid can withstand before breaking.

Hardness

The hardness of a solid is its ability to resist scratching or indentation. The hardness of a solid depends on its atomic structure and its chemical bonds.

There are several different ways to measure the hardness of a solid. One common method is the Vickers hardness test. In this test, a diamond pyramid is pressed into the surface of the solid. The hardness of the solid is determined by the size of the indentation.

Toughness

The toughness of a solid is its ability to absorb energy without breaking. The toughness of a solid depends on its strength, its plasticity, and its other mechanical properties.

Toughness is an important property for materials that are used in applications where they are subject to impact loads. For example, the bumpers on cars are made of tough materials to absorb the impact of a collision.

Applications of mechanical properties of solids-

The mechanical properties of solids are important in many different applications. For example:

·         Engineers: Engineers use the mechanical properties of solids to design structures and machines.

·         Materials scientists: Materials scientists develop new materials with improved mechanical properties.

·         Geologists: Geologists use the mechanical properties of rocks to understand the formation and movement of the Earth's crust.

·         Biologists: Biologists study the mechanical properties of biological materials, such as bones and muscles.