How to Tell How Much Force Is Exerted by a Compression Spring?

Measure the compression force in a spring with some simple tools.

Hooke's law determines the size and direction of the force in a compressed spring. For a compressed spring, the force points in the direction opposite of the compression direction. The force directly depends on the linear distance the spring has been compressed and a quantity know as the spring constant. The spring constant is unique to a given spring and is found experimentally by hanging an object from the spring hung vertically. The amount of weight hung on the spring and the distance it stretches allows you to calculate the spring constant.

Things You'll Need

• Tape Measure
• Scale
• Calculator

Instructions

Find the Spring Constant

1. Hang the spring vertically such that its sides don't touch anything.

2. 

   Measure weight with a scale.

   Place an object on a scale to determine its weight in pounds. Choose an object that will not make the spring stretch more than half its length, so you do not damage the spring. As an example, say the object weighs 0.50 pounds.

3. Convert the weight of the object to newtons, the scientific unit for weight, by multiplying by 4.45, since a pound is equivalent to 4.45 newtons. Performing this operation, 0.50 times 4.45 equals 2.23 newtons.

4. 

   Utilize a tape measure for determining distances.

   Hang the object from the bottom of the vertically hung spring and measure the amount it stretches in centimeters. For the example problem, assume it stretches 10 centimeters.

5. Convert the stretch distance to meters by dividing by 100, since 100 centimeters are in every meter. Now you have a stretch distance of 10 divided by 100 or 0.10 meters.

6. Divide the weight of the object by the stretch distance to obtain the spring constant for the spring in newtons per meter. Continuing the example, 2.23 newtons divided by 0.10 meters equals 22.3 newtons per meter.

Calculate the Compression Force

1. Lay the spring flat on a table with one end against a wall.

2. 

   Use a tape measure for distance measurements.

   Compress the spring towards the wall with one hand while you measure the distance in centimeters the spring has been compressed with your other hand. As an illustration, assume it has been compressed 5 centimeters.

3. Convert the compression distance to meters. Accomplish this by dividing by 100. Now you have compression distance of 5 divided by 100 or 0.05 meters.

4. Multiply the spring constant by the compression distance to solve for the compression force in newtons. Completing the sample problem, 22.3 newtons per meter times 0.05 meters yields a compression force of 11.2 newtons.

Tips & Warnings

• Metric units must be used when employing Hooke's law.

References

• HyperPhysics at Georgia State University: Hooke's Law
• Eric Weisstein World of Physics: Spring Constant
• "Physics for Scientists and Engineers with Modern Physics"; Raymond A. Serway and John W. Jewett; 2009