Engineering Calculations: Density, Stress and Strain
The core engineering calculations: density, stress, strain and the Young modulus. How to choose the right formula, put in the numbers and give the answer with the correct unit.
Get the method right under pressure
Free interactive practice on the steps that lose marks under exam pressure.
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Numbers in engineering
Engineers do not just build things; they calculate to check that a design will work and stay safe. This module covers four key calculations: density, stress, strain and the Young modulus. Getting the formula, the numbers and the units right is what earns the marks.
Calculation terms
Learn what each quantity measures before you calculate it.
Stress vs strain
These two are easy to muddle, so keep them apart.
Rearrange and keep units
In a calculation question, write the formula, put in the numbers, then give the answer with its unit. You can rearrange a formula to find any part: if you know two of the three quantities, you can work out the third. Marks are given for the working, not just the final number.
Match the formula
- density
- stress
- strain
- Young modulus
- mass divided by volume
- force divided by area
- extension divided by original length
- stress divided by strain
Match the unit
- mass
- force
- density
- strain
- kilograms
- newtons
- kilograms per cubic metre
- no unit, it is a ratio
Work out the stress
A force of 100 newtons acts on an area of 5 square metres. Stress is force divided by area. What is the stress?
- 20 newtons per square metre.
- 500 newtons per square metre.
- 95 newtons per square metre.
- 0.05 newtons per square metre.
Found by dividing
Select the TWO quantities you work out by dividing one measurement by another.
- Density.
- Stress.
- The colour of a metal.
- The name of a material.
Do the calculation
Put the steps of answering a calculation question in order, earliest first.
- Write down the correct formula
- Put in the numbers you are given
- Do the division to get the answer
- Write the answer with its unit
Complete the formulae
Density is found by dividing mass by _____. Stress is force divided by _____. Strain is the extension divided by the original _____. The stiffer a material is, the higher its Young _____. In a calculation, marks are given for showing your _____.
Work out the density
A block has a mass of 60 kilograms and a volume of 20 cubic metres. Density is mass divided by volume. What is the density in kilograms per cubic metre?
Find the pascal quantities
Tap the TWO quantities that are measured in newtons per square metre.
- stress
- the Young modulus
- density
- strain
Which quantity is it?
Read each calculation and choose which quantity it works out.
- You divide a force by the area it acts on
- You divide the mass of an object by its volume
- You divide the extension by the original length
Explain a calculation
Explain how to calculate the density of an object. Describe what you would measure, the formula you would use, and the unit of the answer.
- Describe the two things you would measure
- State the formula for density
- Give the unit the answer is written in