Force & Extension (Oxford AQA IGCSE Physics)

Force & Extension

• When a force is applied to an elastic object such as a spring, the object will stretch

  • The object will store energy in its elastic potential store

• The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

  • Directly proportional means that if you change the value of one variable, the value of the other variable will change by the same proportion

    • So if you double the force, the extension will also double

  • The limit of proportionality is the point at which a stretched object will no longer return to its original shape when the force is removed

Force, load and extension of a spring

• The force applied to an elastic object can be calculated using:

• Where:

  • F = force in newtons (N)

  • k = spring constant in newtons per metre (N/m)

  • e = extension in metres (m)

• This equation is known as Hooke's Law

• You may need to rearrange this equation in the exam, a formula triangle can help

Formula triangle for force, extension, spring constant

• The spring constant represents how stiff a spring is

  • The greater the spring constant, the greater the stiffness

• The extension of an object can be calculated by:

Extension = final length – original length

• The extension of the spring can be measured by marking the position of the bottom of the unstretched spring

• When the spring is stretched, the final length must be measured from the bottom of the spring

Measuring the extension of a spring