Mass of an object is the amount of matter present in that object, where as volume of an object is the amount of space that object is occupying. Consider a kilogram of cotton and a kilogram of iron, obviously both have same mass, however cotton would require a lot more space to store it than iron of the same mass. Isn’t it? Now that is because cotton occupies more space (volume) than iron for the same amount of mass.

(Now do not confuse mass with weight, see the difference between mass and weight here.)

Mass is Constant, Volume is Not

Mass of an object always remains the same, but its volume can change depending on the external (surrounding) factors like temperature, pressure etc. Take water for instance, a kilogram of water when cooled into solid ice occupies more volume compared to its liquid state.

Volume and Temperature

Matter usually occupies more volume when its temperature increases because its atoms and molecules acquire more energy on heating and tend to move out a lot there by occupying more space. The only exception to this rule is ice becoming water on heating in which case it occupies lesser space.

Most liquids when heated become gas and gases occupy more volume than liquids. Conversion of water into water vapor is an example of this.

Volume and Pressure

Matter again occupies less volume when there is more pressure and vice versa. Consider blowing air into a cycle tyre. The air is compressed and hence under pressure inside the tyre and hence is occupying less volume. The same is the case with balloons. When you leave the air out of a automobile tyre by deflating it or by deflating a balloon, the air coming out experiences less pressure and hence expands to occupy more volume.

Thus we have seen that volume depends on external factors like pressure, temperature etc while mass of an object does not depend on any external factors and is always a constant.

Mass is a Fundamental Unit. Volume is a derived Unit.

A fundamental unit in physics is a unit whose value does not depend on any other units. For instance, distance does not require any other value to be calculated before calculating distance. So it is a fundamental unit, where as calculating speed requires that you calculate both distance traveled as well as the time taken to travel that distance, and hence it is a derived unit of distance and time.

Mass is a fundamental unit, you do not need to calculate anything else to calculate mass. But Volume is a derived unit because you need to calculate the length, breadth and height of an object to calculate its volume.

Measuring Mass and Volume

Mass is measured by weighing it along with another object of known mass on a scale. For instance see how a kilogram of sugar is measured using scale balance. Object of known mass on one size when balanced by an object of unknown mass indicates that both have same masses, and that is because both are equally pulled by earth’s gravity (which is what we call weight). Gravity of earth or gravity in general exerts equal force (or pull) on equal masses and this principle is used while calculating mass using scale balance.

Volume on the other hand being a measurement of space occupied is measured by using containers of predefined volume. For instance consider measuring a litre of milk, which is done by taking a container (a can or a tin) whose volume is one litre and pouring milk into it till it is full, and this indicates that the container now has one litre of milk.

Table of Differences between Mass and Volume

Finally, Volumes have been written about mass in physics compared to volume. Isn’t it?

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• What is the Difference between Mass and Weight

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