The science of the movie "Gravity".

[Scuba]

I saw "Gravity" Saturday night and particularly enjoyed the special effects. One question, though ...

In an early scene, two astronauts on a space walk gone bad are tethered to each other, and one attempts to use his "jets" to maneuver back to the shuttle. When the slack goes out of the tether, he experiences a tug.

But in space, would he feel a tug from a weightless astronaut on the other end of the tether? This question led to a discussion of weight vs mass, but the issue was not resolved.

Please help shrink the vast universe of my ignorance: was the tug inappropriate?

[rdharma]

1. Newton's third law of motion nt

[ret5hd]

2. Yes he would...the issue is mass, not weight.

[Foolacious]

3. The tug is correct.

And it is indeed a question of weight versus mass.

Try a thought experiment:

1. Our weightless (but not massless) astronaut is tethered to a tennis ball. What happens when the line goes taut? The astronaut and ball feel a tug. The tug is strong enough to really yank the ball, while the astronaut barely feels it.

2. The astronaut is tethered to the space station (which is, of course, weightless but not massless). When the line goes taut, the astronaut and the station feel a tug, strong enough to yank the astronaut while barely affecting the much more massive station.

3. The astronaut is tethered to another astronaut (presumably of about the same mass). When the line goes taut, both astronauts feel a more-or-less equal tug.

Make sense?

[rock]

9. Try: the astronaut is tethered to the earth

Do you think when the rope goes taunt the earth will not pull back but just soar along with him?

[valerief]

16. The earth has gravity, so the astronaut on a rope tied to the Earth would be lying on the ground. nt

[rock]

17. Or if one prefers

The earth would be lying on the astronaut.

[valerief]

18. Ha! Only if the astronaut had more gravity than the earth. nt

[greiner3]

19. He/she would if they ate a LOT of HFCS.

[rgbecker]

4. Yes, for sure, the mass of astronaut would cause a "Tug".

Although weightless, that is; no force of gravity would be causing the astronaut to "fall" down or towards anything, it still requires a "force" to move an object of mass from a stationary position. That force would show up as slack going out of tether, thus the "tug".

The fact a "jet" (probably rocket) would be needed to move the first astronaut shows the need for a force to move anything around out there in space. Too, the constant worry of crashing into something shows the concern that a "force" would be needed to stop a moving object. The crash would be an example of an opposite of the "tug" force.

Hope this helps.

[Atman]

5. I just read an article about this.

Unfortunately I didn't bookmark it. It was about the science of "Gravity." The article ran many of the key scenes by scientists, and they determined the movie was remarkably accurate in terms of the physics of space. The one scene they said was not accurate sounds like the scene you're describing (I haven't seen the movie). Something about the second astronaut being pushed away during this attempt to get back to the spacecraft. The scientists said this could not happen because of zero gravity. Just sayin.' I'll try to find the article, but it did contradict the other responses here.

[Foolacious]

7. I'm sure it didn't contradict these responses.

I'll be interested to see the article. I can assure you, there will be a tug. (Yes, I have an almost BA in physics. One class and one thesis short. :-| ) If there weren't, that would mean that neither astronaut had any inertia, and therefore there would have been no reason for the line to go taut; the tiniest, most microscopic tension on the coiled line would be enough to keep the astronauts from drifting apart.

[Atman]

8. I found a different article, but not really worth posting...

It spoke about both the tug and the release of Clooney...merely releasing Clooney from the tether wouldn't have caused him to float away, as both he and Bullock were both traveling at the same velocity as the Space Station, and therefore he would have pretty much stayed in a stationary position. It went on to say that it would have taken virtually no effort to us the tether to pull him back in, and that he would not have been causing any drag in the first place, because of the zero gravity.

[Foolacious]

10. I'd still like to see the article...

... if you wouldn't mind posting a link.

[DCBob]

6. That part made sense to me since any object has mass regardless of movement... but..

the part when Clooney released himself said he was causing a drag on Bullock made no sense to whatsover. If he was stationary then all she had to do was slowly pull him in... that wouldnt take a tremendous amout of effort or strength.

[pokerfan]

11. Weightless but not massless

There is still inertia and it still takes force to move an object. Still, F=ma applies and even the smallest tug would produce a small acceleration... Phil Plait explains the science of Gravity:

Spoilers!

On Earth, if one person is hanging by a rope and holding on to a second person, yeah, gravity is pulling them both down, the upper person bearing the weight of the lower one. If the upper person lets go, the other falls away. But in orbit, they’re in free-fall. Gravity wasn’t pulling Clooney away from Bullock; there were essentially no forces on him at all, so he had no weight for Bullock to bear! All she had to do was give the tether a gentle tug and Clooney would’ve been safely pulled toward her. Literally an ounce of force applied for a few seconds would’ve been enough. They could’ve both then used the shroud lines to pull themselves to the station.

http://www.slate.com/blogs/bad_astronomy/2013/10/04/ba_movie_review_gravity.html

[Warpy]

12. I don't think you'd feel the tug, not enough mass

unless the other person was using his jet pack going the opposite direction. Then you'd have two stronger forces acting against each other.

In this case, the line would tighten and both would start to travel the same direction.

[X_Digger]

13. Neil deGrasse Tyson is not impressed..

http://www.businessinsider.com/neil-degrasse-tyson-critiques-gravity-2013-10

[pokerfan]

14. Yet he "enjoyed 'Gravity' very much"

http://www.mediaite.com/online/neil-degrasse-tyson-single-handedly-debunks-the-science-of-gravity/

[X_Digger]

15. I know, I know, I was just funning. ;) n/t