What Is Mass and How Is It Measured?

Mass is all around us, and it’s a fundamental concept in physics. But what is it exactly?

Kids are natural observers, and understanding mass at an early age can help them effortlessly grasp physics concepts like gravity later in school. In fact, teaching about mass at a young age can be an invaluable learning tool for many subjects, especially mathematics and science.

Units of Mass

The unit used to measure mass is the kilogram (kg). It is also commonly measured in grams (g) and pounds (lb).

In the metric system, the kilogram is one of the seven base units. Other base units include the meter (base unit of length), second (time), ampere (electric current), kelvin (thermodynamic temperature), mole, and candela (luminous intensity). Derived units like the newton (force) and the joule (energy) depend on these seven base units.

The kilogram is currently defined in terms of a physical artefact—a roughly golfball-sized platinum-iridium cylinder kept in a vault in Paris, France. This practice is not ideal because it introduces uncertainties into the measurement system. Scientists have therefore urged a redefinition of the kilogram based on an unchanging property of nature. This would make the kilogram more accurate and eliminate uncertainty in derived measurements like the newton and joule. Until this happens, however, the kilogram will continue to be a fundamental quantity that we measure.

Density

Density is a measure of how tightly matter is packed together. Isaac Newton was one of the first to provide a clear definition of mass, which he defined as “the quantity of matter” based on its density and bulk (volume).

A material’s density shows how much it weighs in relation to its volume, and is used for comparing the relative weights of different materials. It’s a quantitative property, so it is measured in units such as kg per cubic meter or g/mL for solids, g/cm3 for liquids and g/L for gases.

There are many factors that can affect a substance’s density, including temperature and pressure. For accurate measurements, it’s important to ensure that a sample is homogenous and that the instruments used are calibrated regularly. Buoyancy can also affect the results, especially when a substance is placed in water or another fluid. This can be corrected for in laboratory settings, but it is a consideration when using portable instruments on large scales or in the field.

Force

Whether you are buying a pineapple or designing a space shuttle, mass plays an important role. But it is easy to confuse the terms mass, weight and force. Mass is a measure of the inertia of matter, the tendency of an object to stay in its state of rest or uniform motion unless acted upon by an unbalanced force, such as gravity. Weight is the amount of force exerted by an object’s mass, and is measured in kilograms (kg), a unit defined as 9.80665 newtons at Earth’s surface.

In weighing instruments, the acceleration of gravity acts as a counteracting force to determine mass. NIST combines this method with other techniques, such as comparing the response of two test masses to a given force in order to calculate their relative accelerations. These measurements are monitored with yearly updates of control charts, and more frequent updates if judged necessary from unusual results. These charts also show how the mass standards, called check standards, drift and stabilize over time.

Acceleration

In physics, acceleration is the change in an object’s velocity divided by the change in time. It is usually measured in meters per second squared (m s 2 displaystyle ms2). An example is when you’re driving your car and the speedometer shows that your vehicle has gained 20m of speed over 5 seconds. This is because the acceleration is (20m/s – 0m/s) divided by (5s). The unit for acceleration is newton, named after Isaac Newton, and is symbolised N. All objects on earth are subject to the force of gravity, which has a magnitude of 9.80665 m/s2.

You can demonstrate the relationship between mass and acceleration by performing hands-on experiments with toy cars and hanging weights. You can also analyse data from a table that lists the masses and accelerations of different items. The data will show that, with a constant force, as the mass increases, the acceleration decreases; this is known as Newton’s Second Law of Motion.

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