For example, a locomotive has a greater mass than an automobile. For this reason, it takes more force to stop a locomotive than to stop an automobile if both are moving at the same speed. The unit of mass depends on the system of mechanical units used. One slug equals 14.594 kilograms. Mass and weight are not the same thing.
Weight is the force on an object due to the gravitational pull of a planet or other heavenly body.
An object within a planet's pull of gravity weighs less the farther it is from the planet's surface. However, the object's mass remains constant, no matter where it is. Conservation of mass. The law of the conservation of mass states that mass cannot be created or destroyed. This law has also been called the law of conservation of matter because scientists once thought that an object lost mass only by giving up some of its matter.