Mass is a measurement of how much matter something contains. Objects with more matter have greater mass than objects with less matter.
Unlike weight, mass is not affected by the shape or location of an object. Your body’s mass is the same whether you are curled up on the sofa or standing tall.
Balances are used to measure mass in the laboratory. There are a wide variety of different types of balances. Each type has its own unique set of characteristics that affect how well it functions, as well as the accuracy with which it can be measured. These factors include the physical structure of the balance, the type and density of the objects being weighed, the methods used to weigh the objects, and the handling of the instrument.
The most common balances are known as analytical or precision balances. These are capable of measuring down to one hundred thousandths of a gram. Typically, the analytical balance is located inside of a vented weighing enclosure that has movable doors to prevent air currents from affecting the measurement.
These enclosures also prevent dust and other particles from getting into the weighing pan and impacting the measurement. It is important to note that even the best quality of balances will have errors due to the nature of the measurement process. These may be as simple as balance drift or as complicated as thermal equilibrium, magnetic and electrostatic fields, and human error. The magnitude and significance of these errors will vary depending on the particular laboratory environment and the accuracy required for a specific measurement.
An important factor in determining the accuracy of a balance is its sensitivity. The sensitivity of a balance refers to how much the fulcrum or pivot of the scale needs to move in order for it to read zero. A lower sensitivity will result in more errors while a higher sensitivity will provide more accurate readings.
The biggest factor affecting the sensitivity of a balance is gravitational acceleration. For example, if a highly accurate analytical balance was adjusted perfectly in Tokyo and then carefully transported to Kagoshima, the measurement values for a 1 kg weight would change because of the difference in gravitational acceleration between the two locations. This effect is known as sensitivity error.
Another significant factor affecting the sensitivity of a precision balance is the amount of vibration caused by the weighing procedure. For example, a mechanical balance will vibrate when the weighing pan is moved or when there are large masses placed on the weighing plate. This can cause a reading error which will need to be corrected.
A good quality balance will be capable of achieving very precise measurements by a combination of factors, such as ensuring that the fulcrum is a knife edge for optimal accuracy, using a pointer attached to the beam that amplifies any deviations from the center position of the weighing pan, and employing the principle of moments at equilibrium, in which the anti-clockwise moment created by the standard weights on the left side of the weighing plate is balanced out by the clockwise moment of an object or piece of weighing paper on the right side of the weighing plate. In addition to minimizing these effects, it is important to perform routine inspections of the balance. The simplest inspection is to record the value of the weighing pan at its center and then at each non-center position on the weighing plate and determine if the average of these values is within the tolerances of the sensitivity specified by the manufacturer.