The discussion centers on the physics of movement in space, specifically whether throwing hands upwards can result in downward motion. Participants agree that due to Newton's first law, the center of mass of a body cannot change position without an external force. While throwing hands can create rotational movement, it does not affect the center of mass. The conversation also touches on the concept of expelling mass, such as air or other objects, to create movement in a zero-gravity environment.
PREREQUISITESStudents of physics, aerospace engineers, and anyone interested in the mechanics of movement in space will benefit from this discussion.
If the force from the expelled gas on the cartridge isn't considered to be external, then cartridge and expelled gas are considered one object, whose center of mass doesn't move.stevmg said:Similar to a CO2 cartridge in space, at first "immobile," then the creation of a hole in the tip. The action-reaction to the CO2 rushing out would be motion of the cartridge in the opposite direction when before there was no motion of the cartridge. Note than in this case, too, there is NO external force applied to the cartridge other than what subsequently comes from the potential energy that was contained in the cartridge itself.
Excellent point.A.T. said:If the force from the expelled gas on the cartridge isn't considered to be external, then cartridge and expelled gas are considered one object, whose center of mass doesn't move.
Isn't throwing hands upwards considered as an action? ...I'm confused.athosanian said:I don't think you can move down just by throwing your hand up, because as a whole you are under no force at all. Maybe you can rotate yourself in the space, but the center of mass of your body cannot move at all.
What do you mean?Titania said:Isn't throwing hands upwards considered as an action?
Of course that is an action. The issue you'll run into, if you want to actually travel some distance in space, is that your arms are typically attached to you. If you throw your arms up, that is an action causing an equal and opposite reaction in the rest of your body. But, then your arms reach maximum extension and the force of tension in your arms brings them to a stop, along with the rest of your body which was, briefly, traveling in the opposite direction. Stretching out could let you reach something you couldn't before, but it won't let you go anywhere.Titania said:I'm sorry I sound a bit silly.. But u see, to move your body in space, u will have to exert force or do an action, right? Isn't throwing arms upwards considered as an action? Do correct me.
Okay~ Thanks :)jackwhirl said:Of course that is an action. The issue you'll run into, if you want to actually travel some distance in space, is that your arms are typically attached to you. If you throw your arms up, that is an action causing an equal and opposite reaction in the rest of your body. But, then your arms reach maximum extension and the force of tension in your arms brings them to a stop, along with the rest of your body which was, briefly, traveling in the opposite direction. Stretching out could let you reach something you couldn't before, but it won't let you go anywhere.
Yes, this is correct (I'm assuming you mean "rotate", not move your center of mass). See post #5. This is what everyone in the thread, except stevmg, have said throughout.Titania said:I'm sorry I sound a bit silly.. But u see, to move your body in space, u will have to exert force or do an action, right? Isn't throwing arms upwards considered as an action? Do correct me.