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I was watching this video where the astronauts demonstrate how an object that would weigh some large amount on Earth is nearly weightless in the microgravity experienced onboard the ISS.

What I don't get is, how is it possible for the human to move the object with that relative ease (in comparison to the effort it would take them on Earth)? The mass of the human relative to the mass of that object is still the same. The weight/force acting on both (due to gravity) is the same. To my naive self, the force the muscles would have to apply to move the object remains the same (the mass of the object relative to the human's mass has not changed). Is it just that the rest of the force the muscles would have to deal with has dropped significantly? Is the force generated by the muscles constant irrespective of the gravity the body is subject to?

I do apologize if this is trivial and/or not addressable at this forum.

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    $\begingroup$ Try pushing a two tons boat floating on water. That does not require super strength either. $\endgroup$
    – Winston
    Jun 25 '21 at 7:52
  • $\begingroup$ This is a great and very useful comparison. You should elaborate this into an answer. The principle behind it is very similar $\endgroup$ Jun 25 '21 at 9:53
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On earth we aren't often used to moving massive objects without friction. When we try and move a heavy object across a surface, the friction reduces the acceleration and the velocity doesn't increase much.

Similarly if we tried to lift a large mass straight upwards. Gravity pulls it back down to earth and prevents the upward velocity increasing.

An example where these forces are absent is accelerating a supermarket trolley. If you were in an antisocial mood you could probably easily accelerate a 50kg supermarket trolley and charge down the aisle, say at 10m/s.

In the video the forces above were absent too and by bending his legs, the astronaut easily accelerated the 44kg water container.

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In the ISS there is no gravitational force pulling objects down as there is on earth.

If all surfaces on earth were frictionless, you could push objects with as much ease as you'd push them on the ISS.

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The force the muscles of the astronauts applies for lifting the heavy object has nothing to do with the acc. due to gravity but is due to the acc. by which it lifts the object by his muscles. The weight of the object is less in the ISS but the muscle force has nothing to do with that. As it weighs less, it requires less force of the muscle to lift it.

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    $\begingroup$ « acc ». Why saving a few bytes at the cost of readability? $\endgroup$
    – Winston
    Jun 25 '21 at 7:53
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    $\begingroup$ Maybe saving SE on storage costs? :) $\endgroup$
    – joseph h
    Jun 25 '21 at 8:20

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