Topic 4 - Materials

Question 1

How do you determine stiffness of a spring?

Answer 1

• Spring constant is the stiffness of a spring
• Use F=kx
• On a Force against extension graph this will be given by the gradient

Question 2

How would a student accurately measure the diameter of a wire?

Answer 2

• Take readings in several positions on the wire then find the mean
• This is because the wire may not be of uniform diameter

Question 3

Explain how you would find the Young’s Modulus graphically

Answer 3

• Plot a grah of stress against strain
• The Young’s modulus is the linear gradient

Question 4

What are the part’s of a stress-strain graph?

Answer 4

• Limit of proportionality
• Elastic Limit
• Ultimate Tensile Strength
• Fracture

Question 5

When talking about a stress-strain graph what should you mention?

Answer 5

• Stiffness: Young’s Modulus
• Follows Hooke’s Law up to limit of porpotionality
• Past elastic limit material behaves plastically
• Larger increase in strain to stress
• Mention specific value of stress at break point

Question 6

How would you calculate the elastic potential energy?

Answer 6

• E = 1/2Fx
• Area under force extension graph

Question 7

What are the assumptions you make for stokes law?

Answer 7

Laminar flow