Different objects contain different amounts of matter. Mass is a measure of how much matter an object contains. A metal teaspoon, for example, contains more matter than a plastic teaspoon. Therefore, a metal teaspoon has a greater mass than a plastic teaspoon. An elephant has more mass than a mouse.
When you measure mass, you compare the mass of an object with a standard amount, or unit, of mass. The standard unit of mass is a kilogram (kg). A large grapefruit has a mass of about one-half kilogram. Smaller masses are often measured in grams (g). There are 1000 grams in a kilogram. A penny has a mass between two and three grams.
How can you compare the masses of two objects? One way is to use a pan balance. If two objects balance each other on a pan balance, then they contain the same amount of matter. If a basketball balances a metal block, for example, then the basketball and the block have the same mass. Beam balances work in a similar way, but instead of comparing the masses of two objects, you compare the mass of an object with a standard mass on the beam.
When you hold an object such as a backpack full of books, you feel it pull down on your hands. This is because Earth’s gravity pulls the backpack toward the ground. Gravity is the force that pulls two masses toward each other. In this example. the two masses are Earth and the backpack. Weight is the downward pull on an object due to gravity. If the pull of the backpack is strong, you would say that the backpack weights a lot.
Weight is measured by using a scale, such as a spring scale, that tells you how hared and object is pushing or pulling. The standard scientific unit for weight is the newton (N). A common unit for weight is pound (lb).
Mass and weight are closely related, but they are not the same. Mass describes the amount of matter an object has, and weight describes how strongly gravity is pulling on that matter. On Earth, a one-kilogram object has a weight of 9.8 newtons (2.2lbs). When a person says that one kilogram is equal to 2.2 pounds, he or she is really saying that one kilogram has a weight of 2.2 pounds on Earth. On the Moon, however, gravity is one-sixth as strong as it is on Earth. On the Moon, the one-kilogram object would have a weight of 1.6 newtons (0.36lbs). The amount of matter in the object, or its mass, is the same on Earth as it is on the Moon, but the pull of the gravity is different.