materials

Question 1

What does Hooke’s Law state?

Answer 1

Extension is proportional to force

Hooke’s Law defines the relationship between the force applied to an elastic material and the extension produced.

Question 2

Who discovered Hooke’s Law?

Answer 2

Robert Hooke

Robert Hooke discovered the law in the 17th century.

Question 3

What is the formula for Hooke’s Law?

Answer 3

F = kx

Where F is the force applied, k is the force constant, and x is the extension.

Question 4

What does the constant k represent in Hooke’s Law?

Answer 4

Force constant or stiffness

k is specific to the object being stretched and has units of Nm^-1.

Question 5

How does Hooke’s Law apply to springs?

Answer 5

Extension or compression is proportional to the force applied

For springs, k is also referred to as the spring constant.

Question 6

What types of forces does Hooke’s Law apply to?

Answer 6

Tensile and compressive forces

Hooke’s Law applies equally to both types of forces for most materials.

Question 7

What is the limit of Hooke’s Law?

Answer 7

The elastic limit

Beyond this limit, materials may be permanently deformed.

Question 8

What happens when the elastic limit is exceeded?

Answer 8

The material will be permanently stretched

After force removal, the material remains longer than its original length.

Question 9

What is the point on the graph where Hooke’s Law is no longer obeyed called?

Answer 9

Elastic limit (point E)

The graph shows a transition from linear to nonlinear behavior.

Question 10

How can you combine the force constants of springs?

Answer 10

In series and in parallel

The formulas are: In series: 1/k = 1/k₁ + 1/k₂; In parallel: k = k₁ + k₂.

Question 11

True or False: Hooke’s Law applies to all materials without exception.

Answer 11

False

Hooke’s Law only applies to most materials up to a certain point.

Question 12

Fill in the blank: Hooke’s Law works for _______ forces as well as _______ forces.

Answer 12

tensile, compressive

Both types of forces result in deformation as described by Hooke’s Law.

Question 13

What is tensile deformation?

Answer 13

Extension of a material

This occurs when tensile forces are applied.

Question 14

What is compressive deformation?

Answer 14

Compression of a material

This occurs when compressive forces are applied.

Question 15

What type of materials may only obey Hooke’s Law for small extensions?

Answer 15

Rubber

Rubber exhibits non-linear behavior at larger extensions.

Question 16

What does the graph of force against extension demonstrate?

Answer 16

A straight-line relationship up to the limit of proportionality

Beyond this point, the relationship becomes nonlinear.

Question 17

What is Hooke’s law?

Answer 17

Hooke’s law states that the force exerted by a spring is directly proportional to the extension of the spring, provided the elastic limit is not exceeded.

Hooke’s law is often expressed as F = kx, where F is the force applied, k is the spring constant, and x is the extension.

Question 18

What is meant by the elastic limit of a material?

Answer 18

The elastic limit is the maximum extent to which a material can be deformed elastically without permanent deformation.

Beyond this limit, the material will undergo plastic deformation.

Question 19

What is the difference between elastic and plastic deformation?

Answer 19

Elastic deformation allows the material to return to its original shape after the forces are removed, while plastic deformation results in permanent change in shape.

Elastic deformation occurs within the elastic limit, while plastic deformation occurs beyond it.

Question 20

What happens to the atoms in a material when it is under elastic deformation?

Answer 20

Atoms are pulled apart slightly from their equilibrium positions, but they return to their original positions once the load is removed.

Question 21

What happens to the atoms in a material during plastic deformation?

Answer 21

Some atoms move positions relative to one another, and they do not return to their original positions when the load is removed.

Question 22

What is the formula to calculate extension in a material?

Answer 22

Extension = new length - original length.

Question 23

What does a straight line on a force-extension graph indicate?

Answer 23

A straight line indicates that Hooke’s law is being obeyed, and the gradient of the line represents the spring constant k.

Question 24

What happens to the force-extension graph when the elastic limit is exceeded?

Answer 24

The graph will start to curve, indicating that the material has undergone plastic deformation.

Question 25

What are tensile forces?

Answer 25

Tensile forces are forces that attempt to stretch or elongate a material.

Question 26

What are compressive forces?

Answer 26

Compressive forces are forces that attempt to compress or shorten a material.

Question 27

How can you investigate the effect of force on extension for a length of wire?

Answer 27

Set up an experiment by measuring the original length of the wire, adding weights incrementally, measuring the new length after each weight, and calculating the extension.

Question 28

What safety precautions should be taken during the extension investigation?

Answer 28

Stand up to quickly move away if weights fall, and wear safety goggles to protect your eyes in case the object snaps.

Question 29

What is the formula for calculating stress?

Answer 29

Stress = Force / Area

Question 30

What does the gradient of the stress-strain graph represent?

Answer 30

The gradient represents The Young’s Modulus of a material

Question 31

What is the relationship between stress and strain in the context of the Young modulus?

Answer 31

E = Stress / Strain

Question 32

What does the area under the stress-strain graph represent?

Answer 32

Elastic potential energy per unit volume

Question 33

How is strain defined?

Answer 33

Strain = Extension / Original length

Question 34

What is the Young modulus for a material?

Answer 34

The Young modulus is a measure of the stiffness of a material

Question 35

What are the units for the Young modulus?

Answer 35

Nm^-2 (Newtons per square meter)

Question 36

True or False: The stress-strain graph is a straight line if Hooke's law is obeyed.

Answer 36

True

Question 37

Fill in the blank: The energy per unit volume can also be calculated as _______.

Answer 37

Energy per unit volume = ½ × stress × strain

Question 38

What is the Young modulus (E) calculated from the gradient of the stress-strain graph?

Answer 38

E = Stress / Strain = gradient

Question 39

Describe an experiment to find the Young modulus of a test wire.

Answer 39

Use a thin test wire, apply a known force, measure the extension and original length

Question 40

Why is a thin test wire used in experiments to find the Young modulus?

Answer 40

A thin test wire is used to ensure accurate measurements and minimize errors

Question 41

What is the Young modulus of the wire calculated from the given gradient?

Answer 41

E = 4 × 10^10 Nm^-2

Question 42

What happens to a material subjected to a pair of opposite forces?

Answer 42

It may deform, i.e. change shape.

Question 43

What are tensile forces?

Answer 43

Forces that stretch the material.

Question 44

What are compressive forces?

Answer 44

Forces that squash the material.

Question 45

Define tensile stress (o).

Answer 45

Tensile stress is defined as the force applied (F) divided by the cross-sectional area (A).

Question 46

What are the units of stress?

Answer 46

Nm² or pascals (Pa).

Question 47

Define tensile strain (s).

Answer 47

Tensile strain is defined as the change in length (extension) divided by the original length of the material.

Question 48

What are the units of strain?

Answer 48

Strain has no units; it's just a number.

Question 49

True or False: The same equations apply to tensile and compressive forces.

Answer 49

True.

Question 50

What is the Ultimate Tensile Strength (UTS)?

Answer 50

The maximum stress that a material can withstand before breaking.

Question 51

What happens as a greater tensile force is applied to a material?

Answer 51

The stress on the material increases and starts to pull the atoms apart.

Question 52

What is breaking stress?

Answer 52

The stress at which atoms separate completely and the material breaks.

Question 53

What do engineers consider when designing a structure?

Answer 53

The UTS and breaking stress of materials.

Question 54

What is elastic potential energy?

Answer 54

The energy stored in a stretched or compressed material.

Question 55

What does the area under a force vs. extension graph represent?

Answer 55

The work done in deforming the material.

Question 56

What happens to the work done before the elastic limit?

Answer 56

All the work done is stored as potential energy in the material.

Question 57

Fill in the blank: The stored energy in a deformed material is called _______.

Answer 57

elastic potential energy.

Question 58

What is the formula for Young's Modulus?

Answer 58

Young modulus = tensile stress / tensile strain ## Footnote E = F/A / (x/L) where F = force in N, A = cross-sectional area in m², L = unstretched length in m, and x = extension in m.

Question 59

What are the units of Young's Modulus?

Answer 59

N/m² or pascals ## Footnote Since strain is dimensionless, the units of Young's Modulus are the same as stress.

Question 60

What does Young's Modulus measure?

Answer 60

The stiffness of a material

Question 61

What is the limit of proportionality?

Answer 61

The point up to which stress and strain are proportional to each other

Question 62

Fill in the blank: The Young Modulus is a constant value when stress is divided by strain below the _____ of proportionality.

Answer 62

limit

Question 63

What is the relationship between tensile stress and tensile strain up to the limit of proportionality?

Answer 63

They are proportional to each other

Question 64

What is the significance of Young's Modulus for engineers?

Answer 64

It ensures materials can withstand sufficient forces

Question 65

What type of wire should be used in the Young's Modulus experiment?

Answer 65

Thin and as long as possible wire

Question 66

What is the first step in conducting the Young's Modulus experiment?

Answer 66

Find the cross-sectional area of the wire using a micrometer

Question 67

How do you calculate the area of a circular cross-section?

Answer 67

Area = πr²

Question 68

True or False: The weight used to straighten the wire should be included in final calculations.

Answer 68

False

Question 69

What should be measured to determine the unstretched length of the wire?

Answer 69

The distance between the fixed end of the wire and the marker

Question 70

What should be done when increasing the weight in the experiment?

Answer 70

Increase the weight in steps and record the marker reading each time

Question 71

What is the purpose of using a mass meter or digital scales in the experiment?

Answer 71

To accurately find the weight added at each step

Question 72

What should you do to ensure accurate measurements of extension?

Answer 72

Use a thin marker and look from directly above the marker and ruler

Question 73

What should be re-measured as the wire is unloaded?

Answer 73

The extension for each weight

Question 74

What must be ensured when unloading the wire?

Answer 74

That you haven't gone past the wire's elastic limit