If I am on the space shuttle and I unbolt a barbell from the wall (that weighs 200lbs on earth) then I can throw it around all day long right?
If that is so then at what level do I lose my supermanlike strength? why do I need a robot arm to remove a big package from the bay? when do I stop just picking it up and chunking it and begin using the cumbersome mechanical arm?
Just to get you started I will only talk about the first law to try and get you to do some learning on your own.
Newton’s First Law States:
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
This simply means that to move an object you need to apply a force. This force requires work/energy. The more you move something the more work/energy is used. Since you do not have infinite energy you will not be able to throw around anything indefinitely. And, the more mass it has the more work/energy it requires to move it.
Basically, weightlessness ONLY takes away the acceleration due to Gravity. There is more to the amount of work/energy it takes to move things around than just acceleration due to gravity.
Subjects you might want to explore:
Friction
Momentum
Mass
Acceleration
Force
Inertia
Energy
Work
Force
Relative motion
Are we really weightless when in orbit?
With a basic understanding of these subjects even you could answer this question with adequate clarity.
If you’re, say, 200 lbs and floating in the space shuttle, and there’s a 200 lb barbell floating in the space shuttle, and you try to pull it towards you, you’re also going to pull yourself towards it. You’ll meet halfway.
So, if you want to lift a 2000 lb barbell, well, you’ll pull yourself towards it far more than you’ll pull it towards you.
You may want to specify that in your hypothetical situation, you’ll be firmly attached to an immovable surface, such as a floor or wall.
but what force is required to put a body in motion? I have seen astronauts moving around each other with only their finger. so I would say that the amount of force for Newton’s 1st law is equal to the “weight” of that body. and while we may not be weightless in space we are certainly a very small percentage of that earthbound weight.
Weight is an effect of gravity. In weightlessness, or zero g, it is true you do not have to counter gravity, so you can “lift” or move any mass. But here’s the kicker - you must have leverage.
Assume you unbolt that barbell and “pick it up”. Well, how are you moving it? If you are floating free and it is floating free, then when you grasp it and contract your arms, both of you will move together - and the amount of movement will be proportional to the ratio of the two masses involved. Let’s assume you put your feet against the floor and push with your feet as you pull up. That provided the leverage to allow you to move the barbell without moving yourself. Now then, the barbell is moving across the cabin at some velocity and approaching the end of your reach - how do you stop it? Your feet are not anchored, suddenly you find yourself and the object floating across the cabin together. Until you run into the far wall, or you turn around and catch it with your feet and arms, etc. Only all that momentum takes a lot of effort to stop. Not bad if you gave the push and then you catch it, but it can get tricky if you give two or three good shoves off the walls while moving along, then try to stop all at once. Here’s an example - ever played with a playground merry-go-round, those round wheels you hang on and someone pushes to make them go in a circle really fast? What happens when you push three or four times to build up a really fast rate, and then grab the bars and try to stop it? It pulls you off your feet. See how the effort you added combined to be more than you could remove at one time? Same thing in space. That’s inertia and leverage.
It’s not a matter of losing strength, it’s a matter of adding up more force through multiple actions and then trying to stop the motion with just one.
Another aspect of the problem is independent of the mass of the objects - it is a characteristic of spacewalks. The astronauts can’t walk along like normal, they have to use their hands to crawl along. If they are hand-over-hand crawling, how do they carry that large object? Their hands are already full. Small tools and objects they hook to the suit with tethers or secure to a “tool belt”, but big boxes would be cumbersome. And then throw in the inertial effects and it is easy to do something dangerous and get hurt.
now these astronauts moving around with a finger, is that from a stationary position? let’s say you or the barbell is attached to a wall. in the repetitive motion of starting the weight in motion, stopping it, and moving it the other way, it seems like after a while you would get a slight workout. the main energy-user would have to be the stopping part, because your arms have to be the force which interrupts newton’s first law.
You ignore Newton’s laws at your peril. You can slowly start a heavy object moving, but you’ve go to exert just as uch effort to make it stop. The nice thing abou zero-g is that you can take a reather while you’re “lifting” something and it won’t suddenly crsh to the floor. You can come back to it.
But you pay for this in oher ways – times you expect gravity to be there to help you, and it doesn’t.
Case in Point: Siting down. Here on earth you sort of collapse into your seat, letting gravity pull you down. On Skylab th astronauts soon learned that they had to pull themselves down to sit. Kind of like vertical sit-ups. I understand they had great abs by the time the mision was over.
To what Straight Dope column does this column refer? If no one can find a relevant column I’ll either close this thread or move it on to “General Questions”.
moderator, «Comments on Cecil’s Columns»
We can do a similar experiment right here on Earth. Find something big and heavy, on well-lubed wheels. A large filing cabinet might work, for instance. Now, push on it. Since you’re not trying to lift it, gravity is irrelevant here, but the mass still matters. Since it’s so massive, it’ll take you a while to get it up to a respectable speed. By the same token, once it’s up to speed, it’ll be just as hard to stop. You could push it around with one hand, or one finger, but since you’re exerting that much less force, it’ll take that much more time to get it up to any given speed. It’s the same situation on the Shuttle.
For your second question of how high up you need to be: It doesn’t matter how high you are; what matters is whether you’re in orbit. The Earth’s gravity at the Shuttle’s height is over .8 g, so if you were in some sort of really tall tower, you’d feel like almost your “normal” weight. So why doesn’t the Shuttle fall? It does, as does everything in it, but they all fall at the same rate, so everything seems to float around inside, and they’re falling around the Earth, not towards it, so they never hit. If it weren’t for pesky things like the atmosphere and mountains getting in your way, you could go into orbit a half-inch above the Earth’s surface, or even below the surface, and you’d be weightless relative to your "space"craft.
Leave this one open, Noodles; it’s a good question.
Awright, I’ll bite.
“Noodles”???
Yes, of course, Noodles. What do you call the illustrious moderator of this fine forum?
Nope, not “weight”. The amount of force is proportional to the mass of that body.
General Questions, it is.
I’ll do the honors.
JustinH… (Do you have a brother named “Triple”? Nevermind…)
Do you remember how FAST these astronauts are moving? Not very fast, I assure you.
Try this experiment: Get a big, beefy, massive guy. Have him stand in front of you. Now, get into a shoving match… you shove him, he shoves you. When you shove him, you should notice that he doesn’t move a whole lot, while you get a lot of “rebound”. However, when he shoves you, you go flying across the room, ricochet off the jukebox, slide under the pool table, and ultimately crash into a garbage can, which collapses and spills nasty, slimey filth all over you. The other patrons of the bar will most likely laugh at you. When you get up, wipe the garbage slime out of your eyes, you will notice that Mr. Beefy didn’t seem to move in the slightest.
Now you know not to mess with things bigger than you… even if you’re floating in the vacuum of space.
Chronos…
I call him Goldenrod. I’ll call him much worse if he doesn’t go to the Dopefest in October (Psst! Arnold! Hint, hint!)