Most scientists in the world use the metric system. This makes sense, since it has easy-to-remember prefixes like meter (kilometer), gram and liter.

While mass and weight often get confused, they are not the same things. Mass reflects the amount of matter an object contains, while weight depends on the gravitational pull of an object’s environment.

Units of Mass

Although mass and weight are often confused, they are different physical quantities. Mass is an intrinsic property of matter that determines how strongly an object resists acceleration caused by force.

Weight is a property of the object, determined by its gravitational attraction to the Earth. Objects with greater mass weigh more than objects of lesser mass.

The SI base unit of mass is the kilogram (kg). Other units used to measure mass include gram (g), ton (t), metric ton (mt), and pound (lb).

A group of international scientists has been advocating for a new definition of the kilogram, one that is fixed to an unvarying invariant of nature. They argue that the current definition, which is based on the Paris prototype, injects uncertainty into measurements and invariant constants used in calculations and calibrations. The scientists urge a redefinition based on either the Planck or Avogadro constants. Their proposal has the support of several international science organizations.

Measuring Mass with a Balance

Balances are the most common instrument used in the measurement of mass. They are expensive and delicate and must be handled carefully. When using a balance the container holding the substance of interest is placed on the balance pan and weighed. The initial reading will be the weight of the container itself. The substance is then removed and the balance re-weighs. Subtraction of the second reading from the first gives the mass of the substance taken. This type of weighing is called weighing by difference.

Alternatively, the object of interest can be directly weighed. This requires the balance to be carefully zeroed (reads exactly 0 grams with nothing on the pan). To do this a clean piece of weighing paper is placed on the balance and the balance weighed. The zeroed reading will be the number printed on the weighing paper. Mass can then be read by subtracting the weighing paper from the initial reading. This method of weighing is called direct weighing.

Measuring Mass with a Scale

Although it’s common to use the terms weight and mass interchangeably, they are different measurements. Mass is the amount of matter something contains, while weight is the force of gravity acting on an object.

Mass is measured using balance scales (also known as beam balances and laboratory scales). These instruments consist of a pivoted horizontal lever with arms of equal length, called the “beam” or fulcrum. A pan is suspended from each arm of the balance. The unknown mass is placed in one pan and standard masses are added to the other side of the scale until the balance is in equilibrium.

A gram is a unit of mass in the metric system, which is used by most countries around the world. It is based on the amount of matter in a cubic centimeter of water at standard temperature and pressure. The gram is a SI base unit. It is also the unit of measurement for non-liquid ingredients in cooking and grocery shopping, while liquid ingredients are typically measured by volume.

Teaching Mass to Kids

Kids love measurement because it’s a hands-on, real-life skill that they see all around them. Plus, they get to play games and use their knowledge of the measuring system to solve challenges. This helps to motivate them to learn and practice this new information.

Mass is a physical quantity that tells us how much matter something has. It’s different than weight, which is the force of gravity on an object. The larger the object, the more matter it has and therefore the greater its mass.

To help students understand the difference between weight and mass, encourage them to explore everyday objects in their home or on a walk around the neighborhood. Have them select objects that they are curious about and use a balance to measure them. Then, they can use the cards with gram, kg, and mg to determine which unit of measurement is best to measure them with. They can continue this process until time is up or they have all reached their goal.