[Physics Class Notes] on Unit of Mass Pdf for Exam

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:

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 S
  econd.

• 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.