Chapter 6 Materials

Question 1

What is Hooke’s law?

Answer 1

The force-extension graph is a straight line from the origin up to the elastic limit of the spring.

Question 2

What is the elastic limit and what happens after the force is greater than it?

Answer 2

The elastic limit is the maximum force a spring can withstand without undergoing plastic deformation.

Question 3

What is the unit for the force constant?

Answer 3

Nm^-1

and it is a measure of the force required to extend and object by a unit length

Question 4

With a simple force-extension graph how do you calculate the energy stored in the elastic material?

Answer 4

Area under the graph

Question 5

For a given spring how is the energy stored related to the extension?

Answer 5

The energy stored is directly proportional to the extension^2

Question 6

Equation for energy stored of a spring?

Answer 6

E = 1/2 Fx

Question 7

Equation for elastic potential energy?

Answer 7

E=1/2 kx^2

Question 8

In series how are the force constants combined?

Answer 8

The reciprocals of the force constants are added together just like adding resistors in parallel.

Question 9

How are force constants combined in parallel?

Answer 9

Force constants are added together

Question 10

What does brittle mean?

Answer 10

Brittle materials when subjected to stress fractures with little elastic deformation and without significant plastic deformation.

Question 11

What does ductile mean?

Answer 11

A material that can be stretched into wires or hammered into thin sheets

Question 12

What is a material which is brittle?

Answer 12

Ceramic or glass

Question 13

What is an example of a material which is ductile?

Answer 13

Copper or aluminium

Question 14

Definition of Stress and its unit?

Answer 14

Force applied per cross-sectional area and the unit is Pa

Question 15

Definition of strain and its unit?

Answer 15

Tensile strain is defined as the fractional change in the original length of a wire.

Question 16

At what point on a stress-strain graph is the limit of proportionality?

Answer 16

The point at which the stress stops being directly proportional to the strain.

Question 17

What are the yield points on a stress strain graph?

Answer 17

The yield points are points where the material extends rapidly.

Question 18

What is the ultimate tensile stress of a material?

Answer 18

The UTS is the maximum stress which a material can withstand when being stretched before it breaks.

Question 19

What is the definition of a strong material?

Answer 19

A material with a high UTS.

Question 20

How do you calculate the Young’s modulus of a material?

Answer 20

The gradient of a Stress-Strain graph shows the Young’s modulus.

Question 21

What is Young’s modulus?

Answer 21

The Young’s modulus of a material refers to its ‘stiffness’.

Question 22

What is the loop called from the formation of the loading and unloading curves?

Answer 22

The loop is called the hysteresis loop.

Question 23

What measurements are needed to find out the Young’s Modulus of a material?

Answer 23

Initial length of material

Cross sectional area

extension of material

Tension in material in Newtons

Question 24

What to mention when describing a graph?

Answer 24

Whether it obeys Hooke’s law or not

Question 25

What is meant by plastic deformation?

Answer 25

When a material is permanently deformed

Question 26

Explain why the force constant of two springs in series is halved?

Answer 26

The extension is doubled so the force constant halves.