The mass of an object is a measure of the matter in it. It depends on the number of atoms it contains and the size of those atoms. This property cannot be changed by the location, shape and the speed of the body. The SI unit for mass is the kilogram (kg). Large masses are measured in tonnes ( 1 tonne = 1000kg), and small masses are measured in grams (1g = 10-3 kg).
Masses can be measured by either the sliding mass balance or the electronic mass balance. For the sliding mass balance, the unknown mass is placed onto the pan and its mass is obtained by sliding the movable masses on the beams until the beams are balanced. The electronic balance is more accurate to use than the sliding beam balance. The mass is placed on top of the pan and its mass is displayed on a screen.
Inertia
All objects possess inertia. The inertia of an object refers to the reluctance of an objects to start moving if it is stationary in the first instance or the reluctance of an object to stop moving if it is moving in the first instance i.e. it resists change from its state of rest or motion. Drivers need to wear seatbelts for safety, because if the driver suddenly brakes, he will continue to move forward due to his inertia and crash into a windscreen.