A spring scale measures weight by which principle?

• A. Buoyancy
• B. Electrical resistance
• C. Thermal expansion
• D. Pressure on a spring

Answer: (D)

A spring scale measures weight by the tension created in a spring when gravity pulls on the object. When you hang something, gravity pulls downward, stretching the spring. The stretch follows Hooke’s law (F = kx), so the amount the spring extends is proportional to the weight (a force). The scale is calibrated to convert that extension into a weight reading, typically in newtons or pounds. So the principle at work is the pressure (tension) on the spring produced by the weight.

Buoyancy would change the reading if the object were submerged, electrical resistance isn’t what a simple spring scale uses (though some devices use strain gauges), and thermal expansion isn’t how weight is measured.