What is the Unit of Mass?
Students should learn about mass, as it is very important before understanding the unit of mass. In simple words, mass is the quantity of matter in an object. It can be considered as both a property of a physical body as well as a measurement of its resistance to acceleration when some quantity of force is applied. However, the important point a student should remember is that mass is different from the weight even though the term might sometimes be used interchangeably, as they have different units.
The matter which is present in a given object is known as mass, and the most commonly used units of measurement are:
Gram
Kilogram
Mass can also be termed as the number of atoms and molecules present. In science, mass is measured in metric system units using kilogram (a thousand grams), grams, centigrams (hundredth of grams), and milligrams (thousandth of grams).
Unit of Mass
a. SI Unit of Mass
The standard unit of mass is Kilogram (kg)
In SI units, following units are accepted: gram (g) and its multiples and submultiples, a tonne (t) or metric ton, electronvolt (eV), the atomic mass unit (u) which is most convenient for denoting the masses of atoms and molecules.
b. Cgs Unit of Mass
Centimeter gram second, otherwise the CGS system of units is a metric type system based on centimeter as unit of length, gram as unit of mass, and second as unit of time.
Some Common Units of Mass
Metric Units of Mass
To measure the weight of an object, mass is used. For example, when you step on a scale, you measure the mass of your body.
The most common units to measure mass in the metric system are gram and kilogram.
How much is a Gram?
The mass of a small paperclip is about 111 grams.
How much is a Kilogram?
The mass of a wooden baseball bat is about 111 kilogram.
Measurement of Mass
The amount of matter within an object is represented by mass, but measuring mass doesn't necessarily mean that you have measured weight since weight changes due to gravity's effect. However, mass does not change regardless of where the object is located, the amount of matter remains the same. Depending on the size and location of objects, scientists use various tools to measure mass.
Mass is measured by a beam balance device, also known as mass scales, balance scale, simply scales, mass balance, weight scales, or weight balance.
As mentioned above, a number of tools exist for measuring mass in different environments like balances and scales, measurement transducers, Newtonian mass measurement devices, vibrating tube sensors, and use of gravitational interaction between objects.
a. Balances and Scales
For daily use objects, scientists use a balance to obtain the object's mass. One of the examples of balance is triple beam balance. There are different types of balance, which include beam balances and digital scientific balances. In space, scientists use the inertial balance to measure mass.
b. Measurement Transducer
Sometimes mass cannot be determined by using a balance. Transducers are used by scientists to measure the mass of a liquid in a calibrated tank. It also measures the mass when the properties of the liquid are in a static state. A signal is sent to the processor through a transducer, which makes the mass calculations displayed by an indicator. Taking measured mass of liquid below the transducer, and subtracting the mass of vapor, the mass of a floating roof, the mass of bottom sediment and water yields gross mass.
c. Space Linear Acceleration Mass Measurement Device (SLAMMED)
SLAMMED is one of the most sophisticated mass measuring devices used to measure the mass of humans in orbit, currently stationed on the International space station. SLAMMED is a piece of rack-mounted equipment that is based on Sir Isaac Newton's law of motion, where force equals the product of mass and acceleration. By using two springs that exert force against a person, this device determines the person’s mass via force and acceleration.
Evolution of SI and CGS Unit
In the mid-nineteenth century, scientists had a discussion on how to extend the metric system of physical units such as force, pressure, work, and power. In order to carry out this, there should be a coherent way, a clear choice should be made on what metric units the distance, mass, and time should be provided. A group of scientists along with the Scottish mathematical physicist James Clerk Maxwell and the Scots-Irish physicist William Thomson (later ennobled as Baron Kelvin) was successful in the argument to select the centimeter, gram, and second, and therefore the CGS System was formed.
In 1874, the CGS system was formally accepted and introduced by the British Association for the Advancement of Science. It favors the working scientists, and it has been commonly followed in scientific work for many years. Engineers preferred a system based on larger units due to the reason that the CGS units are relatively small in size. Within a few years, the MKS system which is based on the meter, kilogram, and second, emerged as a competing choice for a coherent system of units.
In the 20th century, commercial transactions, engineering, and other practical areas used metric units or MKS units more. In 1950 there was some discomfort in using the metric units in translating between CGS and MKS units that went against the metric ideal of a universal measuring system.
Adaptation of the meter, kilogram, second, ampere, degree Kelvin, and candela as the basic units for all international weights and measures was done in 1954 at the Tenth General Conference on Weights and Measures (CGPM). The International System of Units (SI) for the collection of units was adapted at the Eleventh General Conference in 1960. These decisions gave the central core of the MKS system over the CGS system. The CGS units are still in use for various purposes, they are gradually being replaced by the SI units.
Differentiation between MKS and CGS Unit
MKS Unit
The unit system in which fundamental or basic quantities such as length, mass, and time are measured in terms of meter, kilogram, and second.
MKS is the abbreviation of Meter, Kilogram, and Second.
They are large scale units used to measure long distances and larger objects
MKS consist of Meter, Kilogram, Second, Newton, Joule, Watt, etc.
It is also called SI unit system or System International system.
CGS Unit
The unit system in which the fundamental or base quantities such as length, mass, and time are measured in terms of the centimeter, gram, and second.
CGS is the abbreviation of the Centimeter, Gram, and Second.
They are small-scale units used to measure small distances and small objects.
CGS consists of the gram, second, dyne, erg, etc.
FAQs on Unit of Mass
1. What is mass and what is its standard unit in the SI system?
Mass is the fundamental property of a physical body that quantifies the amount of matter it contains. It is a measure of an object's inertia, or its resistance to acceleration when a force is applied. The SI (International System of Units) unit of mass is the kilogram (kg). It is a base unit and is defined based on the fixed numerical value of the Planck constant.
2. What is the main difference between mass and weight?
The key difference between mass and weight lies in their definition and dependency on gravity. Mass is the amount of matter in an object and is constant everywhere, measured in kilograms (kg). Weight is the force of gravity acting on an object's mass and can change depending on the location (e.g., on Earth vs. the Moon). Weight is measured in Newtons (N) and is calculated using the formula W = m × g, where 'g' is the acceleration due to gravity.
3. Besides the kilogram, what are some other common units used to measure mass?
While the kilogram is the SI standard, various other units are used for measuring mass depending on the scale and context. Common examples include:
- Gram (g): 1 gram is equal to 0.001 kilograms, commonly used for smaller quantities.
- Milligram (mg): Used for very small measurements, where 1 mg = 0.001 g.
- Metric Tonne (t): Used for very large masses, where 1 tonne = 1000 kilograms.
- Atomic Mass Unit (u or amu): Used to express the mass of atoms and subatomic particles.
- Pound (lb): A common unit in the imperial system, equivalent to approximately 0.453 kg.
4. Why is mass considered a more fundamental property of matter than weight?
Mass is considered more fundamental because it is an intrinsic property of an object, meaning it does not change regardless of the object's location, the forces acting upon it, or its temperature and pressure. Weight, on the other hand, is an extrinsic property as it is entirely dependent on the strength of the local gravitational field. An object has the same mass on Earth, on the Moon, or in deep space, but its weight would be different in each location, making mass the true constant measure of matter.
5. How is the mass of astronomical bodies like planets and microscopic particles like electrons measured?
The methods for measuring mass vary dramatically with scale.
- For astronomical bodies like planets and stars, mass is calculated indirectly by observing their gravitational influence on other objects. For instance, by measuring the orbital period and distance of a moon, we can use Newton's law of universal gravitation to calculate the planet's mass.
- For microscopic particles like electrons and atoms, scientists use an instrument called a mass spectrometer. This device uses electric and magnetic fields to accelerate ions and then measures how much they are deflected. The amount of deflection is dependent on the particle's mass-to-charge ratio, allowing for a precise mass determination.
6. Can an object have mass but no weight? Explain with an example.
Yes, an object can have mass but no weight. This occurs in a location where the net gravitational force is zero, such as in deep space far from any planets or stars. For example, an astronaut floating in interstellar space still has their full mass (e.g., 70 kg), which represents the amount of matter in their body. However, since there is no significant gravity to pull on them, their weight would be zero. They would be 'weightless' but not 'massless'.
7. What is the Atomic Mass Unit (amu) and why is it important in physics and chemistry?
The Atomic Mass Unit (amu or u) is a specialised unit of mass used for expressing the masses of atoms and molecules. It is defined as one-twelfth (1/12) of the mass of an unbonded, neutral atom of carbon-12. Using kilograms to describe atomic mass is highly impractical due to the extremely small values involved. The amu provides a convenient scale that simplifies calculations and makes it easier to compare the masses of different isotopes and elements.
8. How does the concept of mass directly relate to inertia and Newton's Laws of Motion?
Mass is the quantitative measure of an object's inertia. Inertia is the resistance of any physical object to a change in its state of motion. This relationship is central to Newton's Laws:
- Newton's First Law (Law of Inertia): States that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external force. An object with greater mass has greater inertia, meaning it is more difficult to start moving, stop, or change its direction.
- Newton's Second Law (F = ma): This formula directly links force (F), mass (m), and acceleration (a). It shows that for a given force, an object with a larger mass will experience a smaller acceleration. Conversely, a greater force is needed to accelerate a more massive object at the same rate.
