Chapter 6

Question 1

What is:

• Tensile Deformation
• Compressive Deformation
• Elastic Deformation
• Plastic Deformation
• Elastic Limit

Answer 1

Tensile Deformation: Changes shape under tension.

Compressive Deformation: Changes shape under compression.

Elastic Deformation: Goes back to its original shape.

Plastic Deformation: Permanent change in shape.

Elastic Limit: Stretched beyond the elastic limit, causes plastic deformation.

Question 2

What is the equation for HOOKE’S LAW?

Answer 2

F = kx

k is the spring constant

k = F ÷ x

^^^^^^^^

Gradient of a Force vs Extension graph.

Question 3

State HOOKE’S LAW.

Answer 3

The extension of a spring is directly proportional to the force applied.

This is true as long as the elastic limit of the spring has not been exceeded.

Question 4

What is this?

Answer 4

A hysteresis loop.

Question 5

What DOES NOT obey HOOKE’S LAW?

Answer 5

Rubber bands do not obey Hooke’s Law.

Question 6

What is the equation for STRESS and what are its UNITS?

Answer 6

σ = F ÷ a

Units : Nm² or Pa

Question 7

What is the equation for STRAIN and what are its UNITS?

Answer 7

Σ = Extention ÷ Original Length

Σ = x ÷ L

Strain has no units, it is a ratio or a percentage.

Question 8

State what each point on the graph represents.

Answer 8

P : Limit of proportionality - Hooke’s Law no longer obeys at this point.

E : Elastic limit.

Y1 & Y2: The yield point - The wire is about to give

UTS (Ultimate Tensile Strength) : Stress at its limit - About to break - The wire begins to thin out.

Question 9

What is the equation for THE YOUNG MODULUS and what are its UNITS?

Answer 9

σ ÷ Σ

Stress ÷ Strain

Units: Pa or Nm²

Question 10

How do you calculate the GRADIENT on a STRESS vs STRAIN GRAPH?

Answer 10

σ ÷ Σ

The Young Modulus is the gradient, which relates to te stiffness of the material.

Question 11

What is the equation for ELASTIC POTENTIAL ENERGY?

Answer 11

½Fx

For a spring that obeys Hooke’s Law:

F = ½kx²