Rowing your boat would not cause you to move. However, if you were to sit in the boat and throw an oar as hard as you could, the boat would move. That’s basically what’s happening when a rocket travels through the vacuum of space. The light exhaust goes one way at a very high speed, and the heavy spaceship goes the opposite direction at a lower speed.
No, of course rockets don’t push against anything. WTF?
A rocket moves by Newton’s laws of motion. Every action is opposed by an equal and opposite reaction. So, if you’re sitting on a skateboard and throw a rock backward, you will move forward. The rock’s mass times velocity will equal your mass times velocity. So a 1 kg rock thrown backward at 10 meters per second will move your 100 kg body forward 0.1 meters per second. Don’t forget to correct for friction. Of course, in space there’s no friction.
A rocket moter works exactly the same way a bucket of rocks thrown off a skateboard works. You blast the reaction mass out the back of the rocket, and the rocket moves in the opposite direction.
Of course, a rowboat won’t work, because you’re in a vacuum, so there’s no way moving the oars around can move you anywhere. In a body of water, oars move you by pushing water backwards so you move forwards. If there’s no water to move backwards, you won’t go anywhere.
The velocity of the material thrown out would depend on the energy of the initial explosion and how much of that energy went into moving the material (as opposed to going into things like light and heat). In theory, the material thrown out could get arbitrarily close to the speed of light.
Somebody else gave this plenty of thought…that is, IF the Sun actually went supernova, which won’t happen since the limit is about 1.4 solar masses and greater…instead, the Sun will just go nova and fade away ever so slowly, while earth turns into an airless cinder.
Actually, as you note, rockets do in fact push against something. That something is the rocket’s own exhaust.
To wit: the rocket exerts a force on its exhaust. The exhaust exerts a reaction force of equal magnitude but in the opposite direction on the rocket.
[damn sun obliterates things mightily]
There is no night side of the earth. As a matter of fact, it’s all night.
[/dsotm]
We’ve got eight minutes to live, huh? Cool…just long enough for me to jerk off one last time. 
The average density of the solar wind in the vicinity of Earth is about 7 protons/cm[sup]3[/sup], so it’s possible that very energetic sounds (such as, say, a star exploding) could be transmitted. It will also have a small but eventually perceptable effect on spacecraft. IIRC, both Voyager spacecraft experienced course alterations due to the influence of the solar wind. As well, one of the phenomina that is anticipated at the heliopause is a sudden increase in the density of particles due to interstellar “winds.”
This does in fact happen. We’ve observed effects of shockwaves (basically sound) from other stars going supernova. The light, however, would be the more immediate concern. Incidentally, it’s probably fair to consider the light to be “part of the explosion”, so part of the explosion would indeed travel at c.
Certainly, you are correct. But something puzzles me: as a kid, I distinctly recall being taught by several different teachers (something reinforced by many diagrams of rocket engines) that an important element is that one end of the rocket is open and the other is closed, and that this imbalance is important in rocket propulsion. The implication being that the energy of the combustion “pushes forward” against the sealed end while there is no such action taking place at the open end, thereby propelling the vehicle forward.
I’m embarrassed to be asking this because I thought I was fairly fluent in at least basic physics, but is there any truth to this view? Is that just another, simpler way of saying the same thing?
The sun’s gonna blow up?
STOP IT!
Go back in time…Throw some instant coffee in the microwave.
If the rocket engine isn’t closed at one end the exhaust from one end would just push rocket fuel out the other end. Because the exhaust is pushing against the fuel and the fuel is pushing against the closed end of the engine and the engine is attached to the rest of the rocket - everything moves together.
BTW, a rocket engine closed on both ends is called a bomb.
The sun is not going to go nova, and the page you linked to didn’t say that.
The sun is eventually (some 5 billion years from now) going to expand to a red giant, at which point the earth may or may not be enveloped in the sun’s atmosphere. It’ll be a near thing and we can’t say for sure because it’s hard to predict exactly how much the earth’s orbit will expand due to the mass loss of the sun (increased solar wind as the sun ages and gets hotter). But it doesn’t really matter – in a billion or so years, the increased temp of the sun will boil away the earth’s atmosphere and seas and it will become an airless cinder anyway.
After a couple hundred thousand or so years as a red giant, the sun will shed it’s extended atmosphere in what will seem like a vigorous explosion to any humans around at the time, but by stellar standards will be a fairly gentle puff. The remaining core of the sun will be a white dwarf. The blown off atmosphere will become a planetary nebula (so called because they look like planets in telescopes, not because they have anything to do with planets).
I suppose it’s true, it just doesn’t seem like a particularly useful observation; rockets are open at one end only so as to direct the exhaust gases; the movement of a rocket does not really come from the material inside pushing against the closed end, but rather, the rocket pushing against -by throwing it away - the expelled exhaust.
That is exactly right. In a closed container, the internal pressure is acting on all points of the container so there is no net shove. Make a hole, and there’s a part of the container no longer experiencing shove, so the shove that is diametrically opposite the hole no longer has anything opposing it.
Like if you put a dozen strong men inside a shed (with a dirt floor, not a wooden one; and just resting on the ground 'cos you were too lazy to dig foundations) and they all push mightily against the shed walls. Assuming nothing breaks and they’re all equally strong, nothing happens. Now open the shed door and the man who was pushing on the door stumbles out and falls over in an amusing manner. Meanwhile the opposite side of the shed now has more force applied to it than the side where the door was just opened, and off it goes.
I’ll agree with that, and add: Rockets work by Newton’s third law of motion, for every action there is an equal and opposite reaction. Because the exhaust (action) comes out the back end, the reaction pushes the rocket forward.
If the rocket were open at both ends, then the action would be pushing it in two opposite ways at once, and so the reaction would also be pushing it both ways at once, and so it wouldn’t really move. (Or to put it another way, there would be no net action and thus no net reaction.)
Do wash up before you touch the pizza, OK?
Except it’s throwing it by it pushing against the closed end. Inside a rocket, you’ve basically got a continuing explosion. Initially, stuff is flying every which way. Some of it’s initally flying back, which is good, but just as much is flying forward. If your rocket had no closed end on the front, these would exactly cancel out, and you wouldn’t go anywhere. But the rocket does have a closed-off front, so the stuff that flies forward ends up hitting it, and bouncing off backwards. It’s through this hitting and bouncing off that force is actually imparted to the rocket.
You are right, I should have posted “expand into a red giant”, and I should have known better. Apologies to all.
Maybe he could pan-fry… oh, never mind.