What is elasticity?

The property of a material to regain its original shape and size after the removal of the deforming force.

What is plasticity?

The property of a material by which it undergoes permanent deformation when the deforming force is removed.

Define stress.

Stress is the restoring force per unit area acting within a deformed body.

What are the three types of stress?

• Tensile Stress: Increases length
• Compressive Stress: Decreases length
• Shearing Stress: Causes angular deformation

State Hooke’s Law.

Within the elastic limit, stress is directly proportional to strain.

What does the stress-strain curve show?

It shows the relationship between stress and strain for a material under tensile stress, highlighting elastic limit, plastic deformation, and fracture points.

Why is steel preferred for construction?

Steel has a high Young’s modulus, meaning it resists deformation better than materials like copper or aluminum.

What is the significance of an "I" shaped beam in construction?

It provides high strength with low weight, reducing bending while using less material.

Why are ropes made of thin wires braided together instead of a single thick wire?

Braided wires increase flexibility while maintaining strength.

How does elasticity help in designing artificial limbs?

Artificial limbs need to be light yet strong, requiring materials with high elasticity to withstand stress without permanent deformation.

A material returns to its original shape after deformation. What is this property called?

Elasticity

Match the correct formula for stress:
1. Stress = Force × Area
2. Stress = Force / Area
3. Stress = Area / Force

Stress = Force / Area (σ= A/F )

Identify the type of stress in each situation:
Pulling a rubber band → ___________ Stress
Pushing on a wall → ___________ Stress
Rubbing your hands together → ___________ Stress

Tensile Stress

Compressive Stress

Shearing Stress

Hooke’s Law states that for small deformations, stress is proportional to strain. (True or False)

True!

What does the yield point in a stress-strain curve represent?
1. The point where a material fractures
2. The point where a material stops obeying Hooke’s Law
3. The point where a material becomes more elastic

 The material stops obeying Hooke’s Law

Fill in the blank

Poisson’s ratio is the ratio of lateral strain to _________ strain.

Longitudinal strain

Why do bridges use I-shaped beams instead of rectangular ones?

I-shaped beams reduce weight while maintaining high strength to resist bending and buckling.

A force of 1000 N is applied to a wire of cross-sectional area 5 × 10^-4 m². Find the stress in the wire.

Stress = Force / Area

A 1 m long wire is stretched by 2 mm under a force. Find the strain.

Strain = Change in length / Original length

A steel wire has a Young’s modulus of 2 × 10¹¹ Pa. If stress applied is 4 × 10⁷ Pa, find the strain.

Using Hooke’s Law:

A 2 m long steel wire (Young’s modulus = 2 × 10¹¹ Pa) is stretched under a tensile force of 1000 N. If its cross-sectional area is 2 × 10^-6 m², find its elongation.

A 2 L sample of water is subjected to a pressure increase of 10⁶ Pa. If the bulk modulus of water is 2.2 × 10⁹ Pa, find the change in volume.

A metal wire is stretched by 0.2% in length. If its Poisson’s ratio is 0.3, what is the percentage decrease in its diameter?

Lateral strain = Poisson’s ratio × Longitudinal strain
=0.3 × 0.2%
=0.06%

A cube of side 10 cm is fixed at the bottom and a force of 5000 N is applied to its top face. If the shearing strain is 0.01, find the shear modulus (G).

Shear modulus formula: