- Forces don’t just change the motion of a body, but can change the size and shape of them too. This is known as deformation
- Forces in opposite directions stretch or compress a body
- When two forces stretch a body, they are described as tensile
- When two forces compress a body, they are known as compressive
- Tensile strength is the amount of load or stress a material can handle until it stretches and breaks
- Here are some common materials and their tensile strength:
Tensile strength of various materials
Remember to read the questions carefully in order to not confuse the terms ‘tensile stress’ and ‘tensile strain’.
- A material obeys Hooke’s Law if its extension is directly proportional to the applied force (load)
- The Force v Extension graph is a straight line through the origin
- This linear relationship is represented by the Hooke’s law equation
- The constant of proportionality is known as the spring constant k
Double check the axes before finding the spring constant as the gradient of a force-extension graph. Exam questions often swap the load onto the x-axis and length on the y-axis. In this case, the gradient is not the spring constant but 1 ÷ gradient is.