Difference Between Mass and Weight
9 Minutes
Difference between mass and weight for students, explaining units, gravity on Earth versus the Moon, and calculations. A science lesson in English.
- How mass measures matter in kilograms while weight is force in Newtons
- Comparing gravity and weight on Earth with the Moon using stone bags
- Converting kilograms to Newtons, digital scales, and the Higgs boson
What this lesson teaches
Mass is the amount of matter contained in an object, while weight is the gravitational pull acting on that mass. Mass is measured in kilograms and stays the same anywhere in the universe, but weight is a force measured in Newtons that changes depending on gravity.
How gravity determines weight
All objects are made of atoms containing electrons, protons, and neutrons, which combine to form matter. Earth exerts a gravitational force that pulls objects toward itself, creating an acceleration due to gravity that depends on Earth's mass and radius. The value of this acceleration on Earth is 9.81 meters per second squared. When an object contains more matter, Earth pulls it with greater force, which increases its weight.
Comparing Earth and the Moon
- A stone with a mass of 10 kilograms experiences 98.1 Newtons of gravitational force on Earth.
- The Moon has a smaller radius and mass than Earth, resulting in a lower acceleration due to gravity of about 1.62 meters per second squared.
- On the Moon, that same 10-kilogram stone experiences only 16.2 Newtons of force, which is roughly one-sixth of its weight on Earth.
- Even though the gravitational pulling force drops significantly on the Moon, the mass of the stone remains exactly 10 kilograms.
Calculations and weighing scales
To convert mass into weight, multiply the mass in kilograms by the acceleration due to gravity. For instance, a person with a mass of 100 kilograms has a weight of 981 Newtons on Earth. Digital scales are calibrated using this relationship. When a person steps on a digital scale, the device actually measures the gravitational force in Newtons and divides it by 9.81 to show the mass in kilograms.
Atomic mass and falling bodies
- Galileo showed that in a vacuum where there is no air resistance, an elephant and a feather dropped together will fall at the exact same time.
- Research between 1964 and 2012 by Higgs showed that an atom contains more than just electrons, protons, and neutrons.
- When the parts of an atom were weighed separately, their combined mass was less than the weight of the complete atom.
- This mass difference confirmed the existence of other particles inside the atom, known as the Higgs boson.