Definition of Stress and strain

Strain*

A rubber band has a original length of 5cm and was pulled longer to 6cm. Thus 1cm difference and we divide difference in length with original length. = 1 divided by 5= 0.2

So in this case, Strain = 0.2 (Strain is a ratio and therefore no units.)

Stress*

Stress is the amount of pull and push force applied over a cross-sectional area and right angle to the action of the force. (The basic S.I. units of stress is N/m2) So, if you have a 20N force applied over an area of 10cm2 at right angle...

Stress = load divided by area

Stress = 20N divided by 0.01m (converting from cm to meter)

Stress = 2000N/m2

Or Stress = 2000Pa = 2kPa

Just remember that Strain* = lenght and Stress* = pressure.