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."
- "The World of Physics"; John Avison; 1989
- metal weight image by berkay from Fotolia.com