I watched the "Helping Hand" episode of Love, Death & Robots on NetFlix, where the protagonist is adrift in space. Every second she is further from her ship, and when her tank is out of oxygen, she throws her glove to propel herself back to the ship.

But I don't know how propulsion works in zero gravity. She needs to throw something heavy to make this propulsion? If she throws something like her watch, will it have the same effect as if she throws her heavy suit gloves?

My question is, if you are in space, and you needs to change velocity, and you have something to throw, is it better to throw the heaviest thing?

  • $\begingroup$ I don't agree with the close votes: while this question was inspired by a TV show, it is not a question about a fictional topic. $\endgroup$ – ahemmetter Mar 20 '19 at 10:59
  • $\begingroup$ Some of the close votes might be for the custom close reason I'd used: "off-topic because questions about fictional topics are off-topic". However, I had second thoughts and retracted that one a while back (simultaneously deleting the comment), because I think this one can be answered with conventional newtonian mechanics. $\endgroup$ – user191954 Mar 20 '19 at 12:23
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    $\begingroup$ Agreed - the episode has some plot challenges, but the physics of this part is all simple Newtonian mechanics. $\endgroup$ – Rory Alsop Mar 21 '19 at 11:07

Yes. For two reasons.

When you throw something, there is a force exerted on you just like you exert a force on the object you throw. Momentum is conserved, so whatever momentum you give to the object you throw in one direction, you gain from the object in the opposite direction.

The first reason you want to throw something heavier is that when you apply a force on a heavier object, it won't have as much of an acceleration as a lighter object. Thus, you can push with the same force that you'd push a lighter object with, but for longer, since the object won't fly away immediately. And since you applied the same force but for a longer period of time, you'll have delivered more momentum to object you pushed, and will have gained more momentum in the opposite direction.

(When in trouble, think of the extremes - a person throwing their watch versus pushing off a massive wall)

The second reason you want to throw something heavier is that the lighter you are, the faster your velocity will be with the momentum gained opposite to the direction you threw the object. By getting rid of heavier things you're carrying, it'll be easier to accelerate with any amount of force applied - you'll have a higher velocity with any momentum you gain.

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  • $\begingroup$ You also have to be careful how you throw the object, otherwise you'll give yourself too much angular momentum. $\endgroup$ – PM 2Ring Mar 21 '19 at 13:20

The force on the, let's say a watch, would be equal to the force acted upon the person due to there always being an opposite and equal force. Given two objects expelled from a person at the same velocity, the one with bigger mass would result in the person having higher velocity.

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  • $\begingroup$ That is not how the episode plays out - she does not use oxygen as a rocket. She has her sleeve sealed off so she can remove her glove. $\endgroup$ – Rory Alsop Mar 21 '19 at 11:07
  • $\begingroup$ I just re-read the question, you're right. I read it too quickly and saw something like the end of the martian before me. Now the follow-up questions make more sense as well. Thank you. @RoryAlsop $\endgroup$ – DakkVader Mar 21 '19 at 13:25
  • $\begingroup$ My 2nd paragraph is still valid and relevant however @RoryAlsop $\endgroup$ – DakkVader Mar 21 '19 at 13:25
  • $\begingroup$ True - I have removed the first paragraph and given you an upvote :-) $\endgroup$ – Rory Alsop Mar 21 '19 at 18:13
  • $\begingroup$ Solid move, thanks! @RoryAlsop $\endgroup$ – DakkVader Mar 22 '19 at 7:41

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