Lesson 1 Basic Stress and Strain

What is the unit of stress?

• Newton (N)

• Pascal (Pa)

• Joule (J)

• Meter (m)

Answer explanation

The unit of stress is Pascal (Pa), which is defined as one Newton per square meter (N/m²). It quantifies the force applied per unit area, making it the correct choice among the options provided.

What does strain measure?

• Change in area

• Change in length divided by original length

• Force applied to an object

• Stress over time

Answer explanation

Strain measures the deformation of a material, specifically the change in length divided by the original length. This ratio indicates how much an object stretches or compresses under stress.

What is the formula for stress?

• σ = F * A

• σ = F/A

• σ = A + F

• σ = A/F

Answer explanation

The correct formula for stress (σ) is σ = F/A, where F is the force applied and A is the area over which the force is distributed. This relationship shows how stress is defined as force per unit area.

What is Young's Modulus?

• Area divided by force

• Stress divided by strain

• Force divided by area

• Strain divided by stress

Answer explanation

Young's Modulus is defined as the ratio of stress (force per unit area) to strain (deformation per unit length). Therefore, the correct choice is 'Stress divided by strain', which quantifies material stiffness.

What does the elastic limit represent in a stress-strain graph?

• The yield stress

• The breaking point

• The point of maximum stress

• The point where the material returns to its original state

Answer explanation

The elastic limit is the maximum stress a material can withstand while still returning to its original shape. Beyond this point, the material undergoes permanent deformation, making "the point where the material returns to its original state" the correct choice.

What is the yield stress?

• The stress at the breaking point

• The maximum stress a material can endure

• The stress at which a material begins to deform plastically

• The stress that causes elastic deformation

Answer explanation

The yield stress is defined as the stress at which a material begins to deform plastically, meaning it will not return to its original shape after the load is removed. This distinguishes it from elastic deformation.

In the context of stress and strain, what does Hooke's Law state?

• Strain is proportional to stress

• Stress is proportional to area

• Strain is independent of stress

• Stress is constant for all materials

Answer explanation

Hooke's Law states that strain (deformation) in a material is directly proportional to the applied stress (force per unit area) within the elastic limit of that material. Thus, the correct choice is 'Strain is proportional to stress'.

What is the breaking point in a stress-strain graph?

• The point of maximum elastic deformation

• The point of maximum stress

• The point where the material breaks

• The point where the material starts to yield

Answer explanation

The breaking point in a stress-strain graph is where the material ultimately fails and breaks. This is distinct from other points like maximum stress or yield point, which occur before the material fractures.

What is the relationship between stress and force?

• Stress increases with decreasing force

• Stress decreases with increasing force

• Stress is independent of force

• Stress is directly proportional to force

Answer explanation

Stress is defined as force per unit area. Therefore, as force increases, stress also increases, making stress directly proportional to force.

What is the formula for calculating strain?

• Strain = Change in length / Original length

• Strain = Stress / Young's Modulus

• Strain = Original length / Change in length

• Strain = Force / Area

Answer explanation

The correct formula for calculating strain is 'Strain = Change in length / Original length'. This definition quantifies how much a material deforms relative to its original size, making it the standard measure of strain.