9 (b) Weight Versus Mass
Weight and Mass: Mass is sometimes confused with weight. Mass is a measure of the amount of matter in an object; weight is a measure of the gravitational force exerted on an object. The force of gravity on a person or object at the surface of a planet is known as weight. Weight varies with the strength of the gravitational force but mass does not. You weigh less on the moon because the moon’s mass is only a fraction of Earth’s.
Inertia Depends on Mass: Some objects have more inertia than other objects. The greater the mass of an object is, the greater its inertia, and the greater the force required to change its motion. How is mass related to inertia?
Gravity: Gravity is a force that pulls objects toward each other. Newton realized that gravity acts everywhere in the universe, not just on Earth. It is the force that makes an apple fall to the ground. It is the force that keeps the moon orbiting around Earth. It is the force that keeps all the planets in our solar system orbiting around the sun.
Factors Affecting Gravity: Two factors affect the gravitational attraction between objects: mass and distance. Mass is a measure of the amount of matter in an object. The SI unit of mass is the kilogram.
The more mass an object has, the greater its gravitational force. Because the sun’s mass is so great, it exerts a large gravitational force on the planets. That’s one reason why the planets orbit the sun.
In addition to mass, gravitational force depends on the distance between the objects. The farther apart two objects are, the lesser the gravitational force between them. For a spacecraft traveling toward Mars, Earth’s gravitational pull decreases as the spacecraft’s distance from Earth increases. Eventually the gravitational pull of Mars becomes greater than Earth’s, and the spacecraft is more attracted toward Mars.
Weight and Mass
Mass is sometimes confused with weight. Mass is a measure of the amount of matter in an object; weight is a measure of the gravitational force exerted on an object. The force of gravity on a person or object at the surface of a planet is known as weight. So, when you step on a bathroom scale, you are determining the gravitational force Earth is exerting on you.
Weight varies with the strength of the gravitational force but mass does not. Suppose you weighed yourself on Earth to be 450 newtons. Then you traveled to the moon and weighed yourself again. You might be surprised to find out that you weigh only about 75 newtons—the weight of about 8 kilograms on Earth! You weigh less on the moon because the moon’s mass is only a fraction of Earth’s.
Gravity: Gravity is a force that pulls objects toward each other. Newton realized that gravity acts everywhere in the universe, not just on Earth. It is the force that makes an apple fall to the ground. It is the force that keeps the moon orbiting around Earth. It is the force that keeps all the planets in our solar system orbiting around the sun.
Factors Affecting Gravity: Two factors affect the gravitational attraction between objects: mass and distance. Mass is a measure of the amount of matter in an object. The SI unit of mass is the kilogram.
The more mass an object has, the greater its gravitational force. Because the sun’s mass is so great, it exerts a large gravitational force on the planets. That’s one reason why the planets orbit the sun.
In addition to mass, gravitational force depends on the distance between the objects. The farther apart two objects are, the lesser the gravitational force between them. For a spacecraft traveling toward Mars, Earth’s gravitational pull decreases as the spacecraft’s distance from Earth increases. Eventually the gravitational pull of Mars becomes greater than Earth’s, and the spacecraft is more attracted toward Mars.
Weight and Mass
Mass is sometimes confused with weight. Mass is a measure of the amount of matter in an object; weight is a measure of the gravitational force exerted on an object. The force of gravity on a person or object at the surface of a planet is known as weight. So, when you step on a bathroom scale, you are determining the gravitational force Earth is exerting on you.
Weight varies with the strength of the gravitational force but mass does not. Suppose you weighed yourself on Earth to be 450 newtons. Then you traveled to the moon and weighed yourself again. You might be surprised to find out that you weigh only about 75 newtons—the weight of about 8 kilograms on Earth! You weigh less on the moon because the moon’s mass is only a fraction of Earth’s.
