Mass

Mass is the amount of matter—“stuff”—contained in an object.

• Mass is measured in grams (g) or kilograms (kg). For example, a 1 kg bag of rice has a mass of 1 kg.
• It depends on how much material the object contains, not on where the object is. A 1 kg rock on Earth, the Moon, or Jupiter still has a mass of 1 kg.
• Mass also affects how hard an object is to start moving or stop moving. A loaded shopping trolley is harder to push than an empty one because it has more mass.
• Mass is different from weight. Weight is a force caused by gravity, so it can change from one planet to another, while mass stays the same.
• In daily life, people often say “I weigh 40 kg,” but 40 kg is actually a mass. Scientific weight is measured in newtons.