Mass and Weight
4 Minutes
Mass and weight for kids: learn the difference between matter, mass, gravity, and how weighing machines work. An English science lesson.
- What mass is by comparing two bottles with marbles
- How gravity creates weight and how weighing machines show mass
- Why weight changes on the Moon and Everest while mass does not
What this lesson teaches
Mass is the amount of matter present inside an object, while weight is the force created when gravity pulls down on that mass. While the mass of an object remains identical wherever it goes, its weight changes depending on the strength of the gravitational force acting upon it.
Matter and mass
Everything surrounding us, such as a table, a pen, or a notebook, is made of matter. To see how mass works, consider two identical empty bottles, one of which is completely filled with marbles. Each marble represents matter, so the bottle filled with marbles contains far more matter than the empty bottle. Since mass is the total amount of matter an object holds, the bottle filled with marbles has greater mass.
Gravity and weight
- The Earth pulls all objects, people, and materials downward through an attractive pull called gravitational force.
- On Earth, this downward gravitational pull acts with a value of around 9.81 meters per second squared.
- Weight is the mass of an object calculated together with the gravitational force pulling on it.
- A measuring scale registers this pulling force and expresses weight in the scientific unit called Newtons.
How weighing machines calculate mass
When a person steps onto a standard weighing machine, the device experiences their weight under the pull of Earth's gravity. To show mass instead of weight, the machine is calibrated for Earth by dividing that weight value by 9.81. This built-in division cancels out the gravitational pull, allowing the display screen to show the person's mass in kilograms.
Why weight changes across locations
- The mass of an object never changes, whether it is measured on Earth, taken to the Moon, or kept in outer space.
- Weight changes whenever the local gravitational force becomes stronger or weaker.
- Because the Moon has a much lower gravitational force than Earth, an object weighs noticeably less on the Moon.
- High locations like Mount Everest have slightly lower gravity, meaning a person's weight decreases slightly at the peak even though their mass is unchanged.