Mass is the amount of matter something contains, while weight is a measure of the force gravity exerts on an object.
Far out in space, you could easily lift a bus, if you had a floor to stand on and could do it before your eyeballs exploded or your body froze.
So, we’re not concerned with the mass of the box we’re lifting, more its weight on earth.
Mass is important, however, as that’s what causes gravity. The moon’s mass causes ocean tides, for example.
There are four fundamental interactions...
Gravitational, Electromagnetic, Strong, and Weak Nuclear forces (these last two are on a tiny scale, acting at subatomic distances).
While gravity is the weakest of these forces, it still kills people every day and injures others both in individual instances and gradually over time.
Einstein’s ‘theory of relativity’ says that if you fall off a building and reach free-fall speed (9.8 meters per second), you’re actually not falling down. What’s actually happening is that the earth is falling UP to meet you. The nature of space-time is not an easy thing to wrap your head around.
A box with an earth weight of 20kg requires care in lifting here, to ensure the human involved is not damaged. This 20kg box would weigh 3.2kg on the Moon, and 7.4kg on Mars.
The earth’s not a bad place to lift something however, compared to taking your box to the gas giant Jupiter (47kg). And, if you had really, really good PPE and you travelled to the Sun, your box would weigh over 500kg.