Which of the following units could NOT be used for normal strain? Select answer from the options below μmm / m yd / yd μin . / in . μg / kg μm / m
Answer
Which of the Following Units Could NOT Be Used for Normal Strain?
Normal strain is a measure of the deformation (stretching or compression) of a material in the direction of the applied load. It is a dimensionless quantity and is calculated as:
Strain (ε) = Change in Length / Original Length
Because it is a ratio of two lengths, strain has no units or can be represented as the ratio of two like units (e.g., mm/mm, m/m, in/in).
Let’s Examine Each Option:
✅ μmm / m – This is valid. Both are length units. Though not the same unit, it still represents a ratio of length/length.
✅ yd / yd – This is valid. Same units cancel out, leaving a dimensionless ratio.
✅ μin. / in. – This is also valid. Microscopic length over inch is still a valid strain ratio.
❌ μg / kg – NOT valid. These are mass units (micrograms over kilograms), which have no relevance in measuring strain. Strain relates to deformation (length), not mass.
✅ μm / m – This is valid. It’s a ratio of micrometers to meters, still expressing deformation per unit length.
✅ Final Answer: μg / kg
Reason: This unit expresses a mass ratio, not a length ratio. Since normal strain only involves measurements of length, this unit is incorrect for strain measurement.