What is mass and the SI unit of mass kilogram
What is mass ?
Mass is defined as the amount of matter an object contains. The basic unit of mass in SI units is kilogram
Newtons second law states that the acceleration of an object is dependent upon two factors. 1) the net force acting upon the object and 2) the mass of the object. Acceleration of an object depends directly on net force acting upon the object, and inversely upon the mass of the object.
In other words, if the mass of the object is more, more force is required to impart a particular acceleration to that object.
The mass is considered as an unchanging property of an object anywhere in the universe. In other words, mass of an object is the same if you measure anywhere in universe. Mass is not related with the gravity of the place where it is kept.
Mass of an object is not same as the weight of the object. Primary difference between mass and weight is, weight of an object is dependent on the gravity of the place where the object is kept. For example; the weight of an object in moon will be less than the weight of same object in earth. The reason is that the gravity on moon is less than the gravity on earth. The weight of the same object will measure more if kept in Jupiter, because the gravity pull on Jupiter is more compared with earth and moon.
The easiest way to measure the mass of an object is measured by comparing it with a known predefined mass of another object. To measure the mass of an object, a balance is used. A balance uses a known predefined mass to measure the unknown mass. Below pictures shows a balance and 1/2 kilo mass block.
During late 1700s, unit of mass kilogram was defined in terms of the mass of one liter of water. In 1879, a protype platinum-iridium alloy cylinder became the reference of the unit of mass for the metric system. CGPM (General Conference on Weights and Measures) on 2018 decided to define unit of mass based on unit of time (seconds) and unit of length (meter), in relation with Planck’s constant. The main reason behind this decision was because of mass of the protype was gradually changing.
Planck’s constant is 6.62607015 × 10-34 joule second. One joule is equal to one kilogram times metre squared per second squared (kg * m2 * s−2 ).
Planck’s constant is equal to 6.62607015 × 10-34 joule second. The value of unit kilogram can be found accuratly if we have accurate value of Planck’s constant. We have units second and the meter already defined. From the above relation, we can find the value of unit kilogram.