Unlike length, time and temperature, mass doesn’t change when you move or alter its shape. Its atomic makeup does, however, but that isn’t necessarily obvious to the eye.
It’s important to teach children about mass early so they can effortlessly grasp the concepts of physics as they progress in school. They are inquisitive creatures, after all.
Units
In physics, mass is an attribute of matter and is often measured in kilograms (kg). Weight, however, is a force that depends on the gravitational attraction of the earth and may be represented by pounds or other units. Although the terms are sometimes used interchangeably, they have different meanings in physics and commerce.
The most commonly used metric unit for measuring mass is the gram (g). Multiples and fractions of the kilogram, a part of the International System of Units, are also used to measure mass.
Other base SI units include the meter (m), the second, and the kelvin. These units are defined by fixed physical constants, which allows them to remain unchanged as science and technology progresses. Each of these base SI units has a distinct name, symbol, and decimal multiples and sub-multiples are formed from the unit names by adding prefixes. For example, the kilogram has a prefix of “g” because it is based on the SI unit gram.
Measurement Procedures
Many chemical measurements involve a mixture of substances that cannot be weighed separately. Using volume measurements, the overall mass of the entire mixture can be calculated. The most common measurement instruments are analytical balances, which can measure down to tenths or hundredths of a gram. They typically use counterweights on three rider beams to counterbalance the pan that contains the sample. They also have a draft shield to keep air currents from disturbing the measurements and are used in conjunction with a weigh boat or weighing sheet that will not react with the samples.
Traditionally, very small masses and forces were measured with sets of carefully calibrated metal weights. These weights, however, are not accurate enough for many modern applications involving manufacturing, medicine and pharmaceutical development. NIST scientists have developed a new measurement technique that self-calibrates, providing mass and force measurements at the submilligram level with precision similar to the international prototype metal kilogram. This new device is based on measuring radiation pressure, and does not require calibration weights.
Accuracy
Among measurement terms, accuracy is a relative term, meaning how close a measured value is to its true or accepted value. In contrast, precision describes how well a set of measurements agree with each other, such as when you get the same number for a particular volume multiple times.
Scientists use the gram and kilogram to measure mass, which is the amount of matter in an object. This includes atoms and molecules, which all have different makeups and therefore differ in mass. Weight is a force caused by gravity, and it can change when an object changes its position on Earth.
For example, a person’s weight can change if they move to another planet. However, their body’s mass stays the same. Engineers who work with structures that must withstand gravity convert the object’s mass into a weight in newtons (by multiplying by 9.8; two significant figures are adequate for this). They then compare the weight to the structure’s strength to determine whether the structure will support the load.
Error
Ideally, for any measurement experiment only one variable should be manipulated. However, that is often not possible due to limitations of equipment and techniques. For example, volume measurements made with a beaker may not be accurate to within the same order of magnitude as those using a graduated cylinder. This results in random errors.
The average of the individual mass error values is referred to as the mass measurement accuracy (MMA). Dmi includes the sign so that positive and negative mass errors partially cancel out when calculating the mass measurement accuracy.
The mathematical model of the distribution of the measured mass accuracy data is usually assumed to be a normal distribution. However, depending on the application of the data you may need to confirm this assumption by applying a statistical test such as the Kolmogorov Smirnov or kh2 (or Chi-squared) test.