How to Calculate the Weight of a Hanging Load on an Extended Bar

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In the field of physics, which includes the study of material objects' interactions with other objects and their surroundings, a weight is considered a force. The force equation used in the case of a hanging load from a bar is Isaac Newton's Second Law of Motion: "F = m_a," where the sum of all forces is equal to the mass of the load times its acceleration. If the load is not moving, that acceleration turns into gravitational acceleration, g. The equation "F = m_g = weight" will be used to determine a hanging load's weight.

    Write down the mass of the hanging load. This will either be provided to you in the problem statement, or it would have been previously determined from prior calculations. The mass should be in units of kilograms. If given in grams, divide the mass by 1,000 to obtain a unit of kilograms.

    Ignore the length of the bar or the string from which the load is hanging. These are irrelevant to calculating the weight of the load. A difference in bar length will only change the distribution of the force along the bar, not the total force itself.

    Multiply the mass in step 1 by gravitational acceleration, g. Gravitational acceleration is a constant, which means that it never changes from problem to problem. Gravitational acceleration equals 9.81 meters per second squared, or 9.1 m/s^2.

    Verify that your units are correct. No units will cancel out in the multiplication procedure. The resulting value will be your force, or weight, in kilogram meters per second squared (kg-m/s^2), which is also known as a "Newton."

References

  • "The World of Physics"; John Avison; 1989

About the Author

Bailey Richert is a 2010 graduate of Rensselaer Polytechnic Institute with a dual bachelor's degree in environmental engineering and hydrogeology, as well as a master's degree in systems engineering. After several years in the environmental consulting industry, she is now attending MIT for graduate school. An accomplished traveler, she has visited 23 countries and published her first book about international travel in 2014.

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