NCERT Class 11 Physics Chapter 9 Notes Mechanical Properties of Solids - Download PDF

Class 11 Physics Chapter 9 Notes: Mechanical Properties of Solids- Download free PDF

Class 11 notes on Mechanical Properties of Solids: Mechanical Properties of Solids is an NCERT chapter that concentrating on how we stretch, compress, and bend our bodies. The NCERT Class 11 Physics chapter 9 notes provide a high-level overview of the chapter Mechanical Properties of Solids. Solids and their mechanical properties, Stress, Strain, Hooke’s Law, Stress- Mechanical Properties of Solids class 11 notes include a wide range of topics, including the Strain Curve and many others.

The chapter's basic equations are also addressed in Class 11 Physics chapter 9 notes. Mechanical Properties of Solids Class 11 notes pdf download covers all of these topics. The CBSE Class 11 Physics chapter 9 notes do not have the necessary derivations.

Also, students can refer,

• NCERT Solutions for Class 11 Physics Chapter 9 Mechanical Properties of Solids
• NCERT Exemplar for Class 11 Physics Solutions Chapter 9 Mechanical Properties of Solids

NCERT Class 11 Physics Chapter 9 Notes

Solids' mechanical properties define properties such as strength and deformation resistance. It represents an object's ability to endure the stress that is applied to it. Objects also have a hard time shifting shape. For example, clay items are easily distorted, hence they have low resistance to deformation, whereas iron objects do not change shape easily. They change shape when heated, indicating that they have a strong resilience to deformation. Clay can be moulded into an earthen pot shape.

Mechanical characteristics:-

1. Elasticity: Elasticity is a quality that allows an object to restore its original shape after an external force is removed. This implies it shows us how flexible a person's body is. Take, for example, a spring. When a spring is stretched, its shape changes, and when the external force is removed, the spring returns to its original position.

2. Plasticity:-It is the opposite of elasticity. The term "property" refers to a state of permanent deformation. Even when the external force is eliminated, the object never returns to its previous shape. Plastics are the name for these types of items.

3. Ductility:- It refers to the ability to be pulled into thin wires or sheets. for example:-Small gold

4. Strength: -The ability to resist a high level of applied stress without failing.

Stress
The restoring force per unit area is known as stress.
When we apply an external force to the body in order to change its shape, the body creates a restoring force in the opposite direction.

As an example:

When an external force is applied to a rubber ball at the same time, the ball creates a force that acts in the opposite direction.

The restoring force is the opposite force that arises in the ball when an external force is applied. Both forces have the same magnitude.

Stress = F/A (mathematically)

Where F is the restoring force that emerges in the body as a result of the force we apply.

A=area

S.I. Unit :- N/m²

Longitudinal stress

When a force is applied to the cross-sectional area of a cylindrical body, longitudinal stress is defined as restoring force per unit area.

Shearing or Tangential Stress

Force per unit area is restored when the applied force is parallel to the cross-sectional area of the body.

There is relative displacement between the opposing faces of the body.

Hydraulic Stress

Hydraulic stress is the restoring force per unit area when a fluid delivers force to the body.

Strain

Strain is a deformation measurement that represents the displacement of particles in the body in relation to a reference length.

It explains how and what happens to a body when it is put under stress.

Mathematically:

- Strain = ΔL/L, where ΔL is the length change.

L stands for the original length.

Because it is a ratio of two quantities, it is a dimensionless quantity.

Strain Types: Longitudinal Strain

The longitudinal tension causes a change in length to the original length of the body. When we apply longitudinal stress to a body, the body either elongates or compresses as a result of the change in length. Longitudinal Strain is a measurement of length change.

Longitudinal Strain = ΔL/L

Shearing Strain

Shearing strain is the measurement of the relative displacement of the body's opposed faces as a result of shearing force. If we apply force parallel to the cross-sectional area, the opposite faces of the body will be displaced relative to each other. Shearing strain is a measurement of how far the two opposing faces have moved away from each other.

Mathematically:-
Consider a cube with an initial length of L that is in a certain position and is shifted by an angle θ. Let x represent the modest relative displacement.

Shearing strain= x/

Volume Strain

The ratio of change in volume to the original volume as a result of hydraulic stress is known as volume strain. When a fluid applies stress to a body, the volume of the body changes without changing the shape of the body.

Volume strain = ΔV/V

Hooke's Law

Within the elastic limit, Hooke's law asserts that the stress developed is directly proportional to the strain produced in a body. Consider a situation in which the body is subjected to external force. As a result, tension arises in the body, and this stress causes a strain in the body, implying that the body will deform. Strain is formed as a result of stress.
According to Hooke's law, as strain rises, so does stress, and vice versa. All elastic substances are subject to Hooke's law. It does not apply to the deformation of plastic. In terms of mathematics:

stress ∝ strain
stress = k × strain

The proportionality constant, k, is also known as the modulus of elasticity.

Stress-Strain Curve

It's a curve that depicts the relationship between stress and strain. The stress (which is the same magnitude as the applied force per unit area) and the strain produced are represented on a graph. The graph demonstrates how a specific material deforms as the load increases. The line that connects O and A is a straight line. This suggests that strain is directly related to stress. Hooke's Law is relevant in this area. The material behaves like an elastic body in this area. Stress and strain are not directly related in the region between A and B. However, as the force is withdrawn, the material returns to its original dimensions. They have elasticity to them.

The yield point B(also known as elastic limit) in the curve indicates that the material will be elastic until this point, and the stress corresponding to point B is known as the material's yield strength (Sy). Elastic region refers to the area between O and B. We can observe that even tiny changes in stress cause strain to increase rapidly from point B to point D. Even when the force is removed, the material does not return to its former location. Stress is zero at this stage, but strain is not since the body has changed shape. Plastic deformation has occurred in the material. It is claimed that the substance is permanently fixed. The ultimate tensile strength (Su) of the material is shown by point D on the graph. We can observe that as we progress from D to E, tension reduces while strain increases. Finally, a fracture occurs at point E. This indicates that the body has broken down.

Modulus of Elasticity

The elastic modulus is defined as the ratio of tension to strain. The elastic modulus is a property of each material.

This means that gold will have a specific elastic modulus value, and rubber will have a specific elastic modulus value, and so on.

Young’s Modulus

Young's modulus is named after the physicist who first defined it.

The ratio of longitudinal stress to longitudinal strain is known as the longitudinal stress-to-strain ratio.

Y is the symbol for it.

Y can be written as longitudinal stress/longitudinal strain

= σ/ ε

Modulus of Shear (Modulus of Rigidity)

The ratio of shearing stress to shearing strain is known as shear modulus.

Modulus of Rigidity is another name for it.

The letter 'G' stands for it.

G=shearing stress/shearing strain

= (F/A)/( Δx/L)

= FL/A Δx

Relation between Young’s Modulus and Shear Modulus

Young's modulus is more than shear modulus.

G = Y/3 is there for most material

Bulk Modulus

The ratio of hydraulic stress to matching hydraulic strain is known as bulk modulus.

The letter 'B' stands for this.

B = -p/(ΔV/V)

Here represents p =hydraulic stress, ΔV/V = hydraulic strain

B(solids) > B(liquids) >B(gases)

Compressibility

Compressibility refers to a substance's ability to withstand compression. Compressibility is the reciprocal of bulk modulus.

The letter 'K' stands for this.

k=1/B = - (1/p) (ΔV/V)

k(solids)<k(liquids)<k(gases)

Significance of NCERT Class 11 Physics Chapter 9 Notes

Revision Aid: The Mechanical Properties of Solids class 11 notes are an excellent resource for revising the chapter, allowing students to effectively recap the main concepts.

Comprehensive Coverage: These Class 11 physics chapter 9 notes cover the core subjects outlined in the CBSE Physics Syllabus in Class 11 and provide a thorough understanding of key topics.

Useful for Competitive Exams: The CBSE class 11 physics ch 9 notes are useful not only for board exams, but also for a variety of competitive entrance exams, including VITEEE, BITSAT, JEE Main, NEET, and others.

Offline Study: Students can access and study the ch 9 physics class 11 notes offline by downloading them in PDF format, giving them more flexibility in their learning approach.

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