C6 Materials

Question 1

Forces that produce extension/compression are known as what?

Answer 1

Extension = Tensile Forces
Compression = Compressive Forces

Question 2

State Hooke’s Law, condition, and formula

Answer 2

• The extension of the spring is directly proportional to the force applied.
• This is true as long as the elastic limit of the spring is not exceeded.
• F = kx

Question 3

What does k represent in F = kx

Answer 3

K = force constant, stiffness of spring, measured in newtons per metre, N/m

Question 4

How to reduce errors when investigating Hooke’s law

Answer 4

• Take measurements using a set square.
• Take readings at eye level to reduce parallax (angle of viewing) errors.
• Use digital balance for mass.
• Draw F against x, gradient = k.
• Area under graph = work done, E (EPE).

Question 5

Formula for elastic potential energy

Answer 5

E = area under graph (area of shaded triangle)
E = 1/2 Fx
E = 1/2 kx^2

Question 6

Relationship between elastic potential energy and extension

Answer 6

Elastic Potential Energy is directly proportional to extension^2, doubling extension quadruples stored energy.

Question 7

Tensile Stress Formula

Answer 7

Force / CSA

Question 8

Tensile Strain

Answer 8

Extension / Original Length

Question 9

Describe Stress over strain graph

Answer 9

• Under the limit of proportionality, the material obeys Hooke’s law, and stress is proportional to strain.
• The gradient of the straight line bit is Young’s Modulus.

Question 10

Define UTS

Answer 10

• Ultimate Tensile Strength is the maximum stress that a material can withstand when being stretched before it breaks.
• Beyond this point, material may become longer and thinner (necking), then reach breaking point.

Question 11

What is Young’s Modulus? Unit?

Answer 11

• The ratio of stress to strain of a particular material, stress / strain.
• Unit is Pa, Nm-2.