What is the difference between mass and weight?

In everyday conversation, we often use the terms mass and weight interchangeably, asking, “How much do you weigh?” when we’re actually referring to the quantitative properties of our bodies. However, to avoid confusion, it’s essential to understand why mass cannot be equated to weight.

The figures displayed on a scale, whether it’s a bag of strawberries or a hypothetical whale, not only help determine the cost of the berries or the size of the whale but also reveal other characteristics.

In scientific terms, mass is a physical value used as a measurement unit for a body, energy, and inertial gravity. This entails certain characteristics in terms of classical mechanics:

1. Mass (m) is invariant: it doesn’t depend on the choice of the reference system. For instance, a passenger on a train or aircraft doesn’t drastically gain or lose weight during the movement of their vehicle. This relativity of the reference system is also inherent in determining speed.
2. Mass is independent of the speed of body movement. However, inertia, the property that requires time to change speed, is determined by mass. For example, an elephant cannot accelerate immediately, while a mouse, being less inert, can change its speed faster.
3. When two bodies interact, their masses are inversely proportional to the ratio of accelerations, a property of inertia. This discovery has helped determine the masses of planets, satellites, and other astronomical bodies, as alternative methods are nearly impossible.

It’s crucial not to confuse mass and weight, the latter being the force with which a body is attracted by the Earth.

In nature, there are no “worlds without gravity,” only worlds of “small and large gravity,” where heavenly bodies are attracted with varying force. An individual’s mass remains stable on different planets, but their weight varies depending on the gravitational force. For example, an astronaut weighing 80 kg on Earth would weigh almost zero in orbit, less than 15 kg on the Moon, and nearly 200 kg on Jupiter. However, their mass remains unchanged in all cases.

In conclusion, while mass and weight are related concepts, they are distinct and should not be used interchangeably. Understanding their differences can help us appreciate the complexities of physics and the universe we inhabit. As always, consult with a science educator or professional for a deeper understanding of these concepts.