Trick question! The Earth weighs nothing at all, but itdoes have a mass of 5.9×1021 kilograms (or in regular figures: 5 900 000 000 000 000 000 000 tonnes). Why the difference? Mass and weight are actually two totally different things. If you think about astronauts orbiting the Earth in the International Space Station, they float around totally weightless. Yet they still have mass and inertia. Weight only exists when something resists the pull of gravity – usually, on earth, by standing on the ground. Gravity pulls downwards with a certain force, and that force is what we perceive as weight. But if you’re not resisting gravity, if you’re falling or orbiting, then you have zero weight. So what does this have to do with the Earth itself? Well, the Earth is also in freefall, drifting through space in orbit around the Sun. Hence, enormous mass, but zero weight.
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