Hooke's law
Materials - OCR A-Level Physics
Key Definition
Hooke's law
The extension of a spring is directly proportional to the applied force, provided the limit of proportionality is not exceeded.
The extension of a spring is directly proportional to the applied force, provided the limit of proportionality is not exceeded.
- The spring constantThe force per unit extension of a spring. A measure of the stiffness of the spring. Measured in N m⁻¹. k measures the stiffness of the spring. A larger k means a stiffer spring
- k is the gradient of the linear region of a force-extension graph
- The limit of proportionalityThe point beyond which force and extension are no longer directly proportional (Hooke's law ceases to apply). is the point beyond which force and extension are no longer proportional (the graph curves)
- $Extension = stretched length - natural (unstretched) length$
- Hooke's lawThe extension of a spring is directly proportional to the applied force, provided the limit of proportionality is not exceeded. applies to springs, wires and many other materials within the proportional region
Common Mistake
MEDIUM
Students often: It's easy to mix up the limit of proportionality with the elastic limit.
Instead: The limit of proportionality is where the F-x graph stops being a straight line. The elastic limit is where permanent deformation begins. The elastic limit is at or slightly beyond the limit of proportionality.
Instead: The limit of proportionality is where the F-x graph stops being a straight line. The elastic limit is where permanent deformation begins. The elastic limit is at or slightly beyond the limit of proportionality.