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# Speed of Curiousity

Posted on 2012-08-29
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The Wiki says it traveled "..36,210 kilometres per hour (22,500 mph).."

The average distance between Mars and Earth is 225 million km(140 million miles).

MQ1: How far, exactly, how fast, and how is a spacecraft going that fast? There's no atmosphere in space; what are the rockets pushing against? There is no friction so you can have great speeds; but how do you get to those speeds? Please answer in easy to understand language...

MQ2: I have a co-worker who does not believe that anyone has been to the moon or to Mars. She says it's a hoax. She survived the layoffs for some unknown reason and plays Angry Birds obsessively. Why do some people not believe that this technology exists?
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Question by:Daydreams

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MA1 : It is due to Newton's third law which states "Every action has an equal and opposite criticism."

MA2 : I personally find it a lot harder to believe you could keep a hoax under wraps than believe the techological challenges could be overcome. You experience amazing technology every day and also people's inability to keep secrets.
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Assisted Solution

Some people got to see to believe. There is no substitute for first-hand knowledge.
The problem with your co-worker's stance is either way she bears false witness as she has no actual first-hand knowledge one way or the other.

Space does have particles, although incommodiously dense, as far as we're aware. Your powers of observation and reasoning are sound, and thus some knowledge may be deduced. Although I am uncertain whether anything anything is impossible, I have heard when you eliminate the impossible, whatever remains, however improbable, must be the truth.
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A1

As stated, if Newton was on a small rowing boat and vigorously threw a heavy bag of sand backwards, the boat would move forward. A rocket uses the same principle and 'throws' its exhaust gasses backward causing the rocket to move forward. The energy gained from the throw increases as a square of the speed of the throw, so the exploding gas makes a very good accelerator.

A2: People that have managed to believe that everybody in the world can be lied ro on such a scale will believe anything as long as it brings harm to someone. They should be avoided.
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Author Comment

> 'throws' its exhaust gasses backward causing the rocket to move forward.

This is what I don't get. In space, what is it "throwing" against?

I am amazed it took only about a year to go millions of miles. It's just awesome.

> They should be avoided.

I wish..
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Not against anything. Try sitting on a bicycle ( Or just do this in your mind) and throw a heavy weight. The bike will roll in the opposite direction. Now try starting near a wall so the thing you throw will hit it. The collision with the wall will make no difference to the way the bike moves.
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Accepted Solution

>This is what I don't get. In space, what is it "throwing" against?

It is not really like that. The ship pushes against the gasses, and the gasses push against the ship.

In a way it would seem to help if there is something to push against but where a jet in the atmosphere has the air to push against it also has the resistence of the air to overcome.

Newton's Third

Simples

Another, including conservation of momentum
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Author Comment

>Not against anything.

I don't think you can go forward without an equal and opposite action. Throwing the weight is essentially pushing against the ground.

>The ship pushes against the gasses, and the gasses push against the ship.

Ahh... That is interesting. I thought the rocket gasses had to push against air, but the ship is pushing against the gasses themselves, which I imagine have air for combustion.

Great links, I believe it is Newton's third law that I was wondering about. The speed is incredible though.
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Author Closing Comment

Tankoo very much for Newton's!!
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>The ship pushes against the gasses, and the gasses push against the ship.

ac hit the nail on the head

It's not so much the push of the gases against anything behind it, but the force of the exiting gases pushing against the ship as they leave.
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It's a very good description.
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ta
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MQ1: How far, exactly, how fast, and how is a spacecraft going that fast? .

Distance 225 million KM aprox.. Speed 36, 210 kph aprox. How does it achieve this speed? Mostly from gravity. They launch the craft towards the moon with the intention of using a sling shoot maneuver. i.e. http://en.wikipedia.org/wiki/Gravity_assist

There's no atmosphere in space; what are the rockets pushing against?

Nothing really. They will only use the rockets (more like short bursts of gas) to make adjustments to the trajectory.

There is no friction so you can have great speeds; but how do you get to those speeds?

As mentioned before. The momentum from the sling shot maneuver is still projecting the craft forward.

I have a co-worker who does not believe that anyone has been to the moon or to Mars.

She's half right. No one has been to Mars.

She says it's a hoax. Why do some people not believe that this technology exists?

I can't say why she doesn't believe, but during the height of the cold war, the first country to put a man on the moon would make the ultimate statement of superiority.  When the motivations were so high, some people tended to think America needed to cheat to win.
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Author Comment

Thanks guys, I was in the process of closing so didn't split as I didn't see your posts. The gravity sling is interesting.
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Expert Comment

Yes, very good point. We were concentrating one the workings of the rocket but the gravity slingshot is a major part of reaching the speeds involved.
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