Choosing the Right Material: Tensile Strength and Strain Calculations

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

Choosing the Right Material: Tensile Strength and Strain Calculations

Learning Objectives

Being able to explain strain in simple words to a classmate

Reproduce and work with the formula for strain 

Being able to explain tensile stress in simple words to a classmate

Being able to explain elasticity

Being able to explain the difference between tensile stress and strain

 Reproduce and calculate with the formula for tensile strength

Introduce the learning objectives and what students will be able to do by the end of the lesson.

Choosing the Right Material

When choosing a material for mountain climbing, lift cables, or hanging a painting, it's important to consider the material's properties.

Explain how the concepts of tensile strength and strain can be applied to real-life scenarios.

mountainclimbing

lift

painting

Drag the cables to the pictures. Which cables would you use for what?

What did you base your choices in the previous slide on?

What is Strain?

Strain is the measure of how much a material is stretched or compressed when a force is applied to it.

Formula: Strain (ε) = Change in length (Δl) / Original length (l)

ϵ=​l​0​​​​Δl​​

Explain what strain is and how it is calculated.

Calculating Strain

Example

If we have an original length of 10 m and a change in length of 0.5 m, what is the strain? 

Data:

required:                                     ε

Workings:

 

ϵ=​l​0​​​​Δl​​

l​0​​=10m

Δl=0.5m

ϵ=​10​​0.5​​

ϵ=0.05

Provide an example for calculating strain to reinforce understanding.

What is the equation for calculating strain?

1. Δl=​l​0​​​​ϵ​​
2. ϵ=​Δl​​l​0​​​​
3. l​0​​=ϵ⋅Δl
4. ϵ=​l​0​​​​Δl​​

If the original length is 8 m and the strain is 0.03, what is the change in length?

1. 3.75 mm
2. 8.03 m
3. 24 cm
4. 266.67 mm

What is the original length if the strain is 0.0004 and the change in length is 0.2 cm?

1. 5 m
2. 16 m
3. 24 m
4. 8 m

What is Tensile Strength?

Tensile strength is the maximum amount of stress a material can handle before it breaks or becomes deformed.

Explain what tensile strength is and how it applies to different materials.

What is Tensile Stress?

Tensile stress is the amource distributed over the cross-sectional area.

So the force per square meter.

Formula:

σ=​A​​F​​

Explain what tensile strength is and how it applies to different materials.

Tensile Stress Formula

Formula:

       in Newton

       in 

        in            or Pa (Pascal)

σ=​A​​F​​

F

A

m​2​​

σ

​m​2​​​​N​​

Explain what tensile strength is and how it applies to different materials.

What is the formula to calculate force for known tensile stress and cross-sectional area?

1. F=σ⋅A
2. F=σ−A
3. F=​A​​σ​​
4. F=​σ​​A​​

What is the unit of tensile stress?

1. Liters
2. Volt
3. ​m​2​​​​N​​
4. Meters

What is NOT tensile stress?

1. Force distributed over cross-sectional area
2. The force per square inch
3. The force per square meter
4. Stress distributed over volume

Formula for Tensile Strength

Tensile Strength (TS) = Force (F) / Cross-sectional area (A)

This is the same formula as for tensile stress, but it is the maximum stress tthe material can handle.

σ=​A​​F​​

Provide the formula for calculating tensile strength and explain how it is used.

Calculating Tensile Strength

If we have a force of 1000 N and a cross-sectional area of 5 m², what is the tensile strength?

 TS = F / A
TS =

 1000 N / 5 m²
TS = 200 N/m²

Provide an example for calculating tensile strength to reinforce understanding.

Look up on the internet which material has the highest tensile strength?

1. Iron
2. Stainless steel
3. Human hair
4. Concrete

Write down 3 things you learned in this lesson.

Have students enter three things they learned in this lesson. With this they can indicate their own learning efficiency of this lesson.

Write down 2 things you want to know more about.

Here, students enter two things they would like to know more about. This not only increases involvement, but also gives them more ownership.

Ask 1 question about something you haven't quite understood yet.

The students indicate here (in question form) with which part of the material they still have difficulty. For the teacher, this not only provides insight into the extent to which the students understand/master the material, but also a good starting point for the next lesson.