# How to Measure Mass and Weight

Until the time of Newton, mass and weight were thought to be the same thing. A ball with 40 kilograms on Earth weighs the same whether it is at the top of a cliff or sitting in your lap.

Precise mass measurements, ranging from transfer reactions to direct measurement, allow mapping of regions far from stability. These maps provide the reference masses from which further investigations using dedicated probes can be undertaken.

## Inertial Mass

Inertial mass is determined by applying a force to an object and measuring its acceleration. Objects of greater inertial mass are more resistant to changes in motion and require a greater force to accelerate them.

The SI base unit for mass is the kilogram, which was defined in 1889 as the amount of matter contained in a standard volume of a platinum-iridium international prototype. Unlike weight, which measures an object’s reaction to gravity, mass is an intrinsic property of matter.

In classical physics, Newton’s law of universal gravitation implies that passive gravitational mass and inertial mass are identical. However, a number of experiments have been performed to see if there is a difference between them, and no evidence exists for this distinction. Einstein’s theory of general relativity, on the other hand, suggests that active and passive gravitational mass are not the same thing. This assumption is known as the equivalence principle.

## Weight

A common way to measure an object’s weight is with a spring scale, which directly compares the mass of the object to the force exerted by gravity on it. This gives an accurate measurement of the object’s weight. In fact, in a gravity field that is uniform over the entire surface of the Earth, an object’s weight is directly proportional to its mass.

However, there are other ways to measure an object’s weight that depend on comparing the object to other objects, rather than a direct comparison of the object to the strength of gravity. These measurements can be used to indirectly estimate an object’s weight, but the result is less accurate than if the object were measured with a spring scale.

A common unit of weight is the kilogram, defined as the sum of an object’s mass and its local acceleration due to gravity. This value remains constant over time. However, many standard customary units for weight also exist, including the avoirdupois pound and the metric ton.

## Density

Density is a physical property that tells us how tightly or loosely a given substance is packed into a fixed volume. It is not to be confused with mass, which relates to the amount of matter contained within an object or liquid.

The SI unit of density is kilogram per cubic meter, but density can also be measured in any unit that represents the relationship between mass and volume. For example, grams per cubic centimeter (g/cm3) is a common unit for measuring density, since density is the ratio between the mass of an object and its volume.

Density is important for understanding how different materials interact with each other. It determines whether an object floats or sinks, for instance. It is also responsible for the currents that we see in the ocean, atmosphere and earth’s mantle. Density is also a key ingredient in the separation techniques used in gold mining, blood separation and strawberry DNA extraction.

## Force

Force is the ability to change a body’s state of motion. It is a vector quantity, meaning it has both magnitude and direction. For an object to move, it must be subject to some force and the direction of that force must be opposite to the object’s velocity (velocity being the change in the object’s position over time).

The SI unit for force is the Newton, defined as one kilogram of mass accelerated at a rate of one meter per second squared under standard Earth gravity. The term ‘force’ is also used in the English system of measurement: a slug is equal to 1 Newton, and in various variants of the Foot-pound-second (English) system it is known as a pound or a poundal; in the metric system it is known as a dyne.

Accurate force measurements are needed in many industrial applications. IMADA offers a wide range of force-measuring instruments, such as tensile test systems to evaluate the strength of fabrics and adhesives, peeling tests for solar cell ribbons and component strength evaluations.

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