What tool is commonly used to measure weight?

A spring scale is commonly used to measure weight because it operates on the principle of Hooke's Law, which states that the force exerted on a spring is directly proportional to how far the spring stretches or compresses. When an object is hung from the spring scale, the weight of the object stretches the spring, and the scale provides a reading based on this stretch. The measurements are typically in units such as newtons or pounds, making the spring scale a direct and effective tool for determining weight.

In contrast, a thermometer measures temperature, a barometer measures atmospheric pressure, and a ruler measures length. Each of these tools serves a distinct purpose and is not designed for weight measurement.