Fjädervågar

Fjädervågar, or spring balances, are mechanical weighing instruments that measure force via a calibrated spring. They are used to determine the weight of an object or its force due to gravity.

Principle: They operate on Hooke's law: F = kx, where F is the gravitational force on the object, k is the spring constant, and x is the spring's extension. The extension moves a pointer over a scale marked in units of force (newtons) or mass (kilograms) based on gravity. The reading corresponds to weight; to obtain mass, one must divide by local gravity or calibrate for gravity.

Construction: Typically a flexible spring anchored at the top with a hook at the bottom where the object is attached. A pointer or sliding scale displays the measurement. Some versions include a tare/zero adjustment and a protective casing. There are various shapes, including U-shaped springs in a frame or a long vertical spring with a dial.

History and usage: The concept dates to early modern science, with practical use expanding in the 19th and early 20th centuries. Fjädervågar were common in shops for weighing goods, in postal services, and for household scales. Today, digital scales largely replace them, but spring balances remain in use for simple, robust measurements and in environments where electrical devices are impractical.

Accuracy and limitations: Readings can be affected by gravity variations (latitude, altitude), temperature, material fatigue, and friction. They are most accurate within a specified range and require periodic calibration with known weights.