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A question about physics.

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posted on Oct, 25 2015 @ 02:03 AM
a reply to: BELIEVERpriest

or you can help me understand.

Try this: put on a pair of ice skates or something with very little friction, take a heavy object like a medicine ball and throw it. Watch as you magically move in the opposite direction.

Same basic principle in rocket science.

The physical law works because it's a physical law. Why do any of them work? Conservation of energy/mass/momentum make sense because you can't make something from nothing, but really we just know that they work: that's why they're laws.

posted on Oct, 25 2015 @ 02:07 AM
a reply to: Ghost147

Your explanation seems to be the most detailed and patient, so I thank you for that, but I still don't get why.

I guess I have trouble grasping the concept because I don't live in a vacuum.

Less resistance=greater thrust, is what I'm understanding so far.

posted on Oct, 25 2015 @ 02:10 AM
a reply to: mc_squared

This makes more sense. Thank you.

posted on Oct, 25 2015 @ 02:18 AM
a reply to: BELIEVERpriest

Everyone needs to start somewhere. I don't see a need to insult anyone for trying to honestly learn

These same concepts apply to things that don't exist in vacuums too, however. The issue is that you're visualizing needing to push off something in order to produce movement. mc_squared's example with the skates and the medicine ball applies very nicely to help your confusion.

You could also think about it this way. Lets say there is an explosion near you right now, what would happen to you if it goes off right behind you? You'd be pushed away from it due to it's force. Just like you see in any action movie when they are running out of a building and a bomb goes off and they go flying. They aren't physically pushing themselves off a solid object, energy alone is pushing them.

"Less resistance=greater thrust" Is also not totally accurate. It just means that the same amount of thrust here on earth or in a vacuum will mean that the object being propelled from the thrust will go a shorter/longer distance because there is more/less resistance.

For instance, if you were to throw a ball across the yard, it would go farther than if you threw the ball with the same force in water. There is more resistance in the water.

posted on Oct, 25 2015 @ 02:19 AM
a reply to: BELIEVERpriest

No worries. Sometimes science can be pretty abstract and it helps to think of examples we can all relate to. Who knows if we'd even get gravity if some British guy didn't get donked on the head by an apple.

This is a double-edged sword though and sometimes (e.g. chair versus wall) it can cause misconceptions that are hard to unseat. Tread carefully.

posted on Oct, 25 2015 @ 02:27 AM
i actually think this is a really good question and none of the explanations are on the same basic level as the question. Everyone is basically saying "its newtonian physics you dummy".

Heres a better answer. Because its just that way.

Why do i like pizza? Because it tastes good. Why does it taste good? Because it does.

Seriously though, does anyone really believe everything they tell us about space?

posted on Oct, 25 2015 @ 02:48 AM

originally posted by: ratsinacage

Seriously though, does anyone really believe everything they tell us about space?

It depends on what "they" are telling you.

A proper physics course will have an annoying amount of demos you will have to do your very own self called "an associated lab course", which will show you that what "they" are telling you actually is true.

And if you keep on going that way, eventually you will reach a point where you are doing your very own proofs ab initio, and that's called science.
edit on 25-10-2015 by Bedlam because: (no reason given)

posted on Oct, 25 2015 @ 02:54 AM

originally posted by: BELIEVERpriest
a reply to: Bedlam
You can continue to make assumptions about my intellectual aptitude, or you can help me understand.

Well, replying to people trying to help you out with "I hear parroting, but no explanation as to why" isn't going to net you a lot of patient assistance.

My comment "there is a lot of basic Newtonian physics stuff out there that would explain it" wasn't intended to be an insult as much as a prompt that maybe some reading is in store if you want the answers you seek.

However, if you're interested in actually understanding it, first, let's figure out where you're starting from. Adult, teen or child? And did you have algebra or basic science yet? Or was it a long time ago and you haven't really thought about it since?

posted on Oct, 25 2015 @ 04:13 AM
am glad you posted this .... not everyone fully understands something .. until we are given the chance to ...

i think i get it ... if i scale it down .. to just a tiny wee thruster in space, combusting a tiny bit of fuel ... as the combustion forces that piece of fuel out, the force separating it away from the thruster ... is the thruster pushing the exploded fuel away .. or is the fuel pushing the thruster .. both ... i see the resulting force, should shift both away from each other proportionally relative to the mass / weight of both objects... either way .. they are distancing themselves, regardless of lack of atmosphere

so .. if i were in space .. and facing someone else .. preferably a woman .. and looking head on, holding hands ...
if we then, exert a force through our arms / hands, and propel ourselves away from each other, regardless of who is propelling who .. we are still able to propel away from each other .. even without atmosphere .. just like the pressure forcing the combusted fuel to be ejected from the thruster ...

So .. in that example .. if a very small person, and very large person, pushed off from each other .. they will both travel away in opposite direction (like thruster on the craft, and the fuel its emitting) ... but as its proportional, it may be harder to see the push away effect on the larger person ... but with lots of small people continually pushing (lots of fuel), and little resistance ... the bigger person would pick up speed soon enough

i think i get it now .. but sorry for the terrible analogy

edit on 25-10-2015 by Segenam because: ... I love to edit ....

posted on Oct, 25 2015 @ 05:31 AM
a reply to: BELIEVERpriest

It is reaction force, because every action has an equal and opposite reaction.

So if you chuck stuff away from you fast & hard enough, you can propel yourself along.

Consider two bricks floating in empty space with a spring compressed between them. The spring pushes the bricks apart and they move away from each other. Because it is empty space and there's nothing to stop them, they'll continue to move apart even when the spring is no longer pushing.

The size of the force pushing apart depends on both mass and acceleration, so, in the case of a rocket, the rocket obviously has more mass than the exhaust but it is accelerating out the back very fast which gives a strong reaction force. The equation is that Force = Mass x Acceleration. The force that pushes the rocket and its exhaust apart is generated by accelerating the exhaust out the back. It isn't pushing against something solid its just two things moving apart relative to each other.

edit on 25/10/2015 by chr0naut because: (no reason given)

posted on Oct, 25 2015 @ 06:06 AM
This is one of those face palm palm moments, when reading the replies his question has been answered 4 times, yet the Op fails to realise this.

The ship is the wall, and the rocket is your hands, that had to be layman enough to understand.

posted on Oct, 25 2015 @ 07:47 AM
a reply to: BELIEVERpriest

No air is needed to "push against" for a rocket to work. Rockets work because of newton's Third Law: "For every action, there is an equal and opposite reaction". That is to say, any system wants to be in equilibrium. For a system to be in equilibrium, all forces related to that system need to cancel each other out.

In the case of the rocket engine, there is a force being enacted in the direction of the rocket nozzle end when propellant is expelled out that end. to keep the system in equilibrium (keeping with Newton's Third Law) the entire system will experience an equal force acted upon it the opposite direction.

edit on 10/25/2015 by Soylent Green Is People because: (no reason given)

posted on Oct, 25 2015 @ 08:11 AM
Same reason you'd move backwards if you fired a gun while floating in space. Soylent has given the best explanation so far I think. To expand on his answer slightly: the craft will eventually reach the speed of the material being ejected from the rocket nozzle if the rocket is fired continuously. The so called photon rocket could theoretically reach the speed of light by ejecting photon radiation however it would accelerate extremely slowly because photons have a low mass.

posted on Oct, 25 2015 @ 08:53 AM
a reply to: BELIEVERpriest

Very well, then why?

Because you think your arms pushing against the wall provide the thrust to move the chair across the room.

In fact, it's your backside that provides the thrust that moves the chair.

posted on Oct, 25 2015 @ 09:25 AM
a reply to: mc_squared

Precisely . A good example and simple

posted on Oct, 25 2015 @ 10:31 AM
Sremmos80's link is about correct. But it is important to note that even though we call it a vacuum in space, it just means there is not organic matter in the mix as much and lower levels of energy particles. There are known and unknown energies in the ether. The reaction of the thrust with these particles is what makes the engines more efficient. These particles are energy particles of all sorts coming from space and from the sun. We cannot see them but they are there.

The earths atmosphere is a plasma, it could be compared to us looking at the water from the air. But there is still substance to space or planets would not be able to retain an orbit and nothing could conduct the lines of connection between the planet and the stars. I am interested to find out what is outside the heliosphere. Will the solar system seem like a lake from outside? I am sure the mix outside the solar system is different than within it. We should know soon if voyager can actually distinguish the difference, the technology was different when it left. They may not have the test equipment necessary to distinguish a difference either.

posted on Oct, 25 2015 @ 11:28 AM
a reply to: BELIEVERpriest

There have been some great answers so far so mine probably won't help.

Imagine trying to kick a football in a pool. it's momentum is halted because the water stopped it. However if you tried to kick a football on land, it would travel further because there is less resistance. And if you you kicked a football in a vaccuum, it would not stop.

posted on Oct, 25 2015 @ 12:05 PM
a reply to: rickymouse

you nailed it. There is STUFF in space that provides resistance to thrust. This is how light and other phenomenae are propagated through space. There is no perfect vacuum. There is no such thing as nothing.

Funny how many smart people who undoubtedly are well educated couldnt articulate such a simple idea.

As a musician i always like to point out how many superb musicians cant teach at all because they just cant break things down verbally or in a way that makes sense to a beginner. This inability exists in all disciplines....get used to it.

posted on Oct, 25 2015 @ 12:08 PM
a reply to: Thecakeisalie

yea but is it fair to compare a football to thrust? football is an object made of fairly stable arrangement of atoms whereas thrust, whether its just pressurized air or chemical combustion is of an entirely different nature and interaction with whatever is in space that provides resistance or interaction.

see this article

this quote says it right

....The idea certainly confounds our day-to-day experience of the world, where change only appears to occur through local interactions. But in recent decades scientific evidence has been building that particles can indeed become “entangled”, so that no matter how far apart they are, they will always be connected

we will eventually confirm that everything is connected.

perhaps the reason why an object in space can continue forever after an initial nudge is not due to a lack of resistance, but because space is a nearly perfect propagating medium in every direction with near perfect homogeneity.

think of it like crowd surfing where peoples hands pass you along all the way down the line......what if particles are connected and just pass objects along in any direction it chooses after the initial thrust?
edit on 25-10-2015 by ratsinacage because: (no reason given)

posted on Oct, 25 2015 @ 12:20 PM
a reply to: ratsinacage

it's not about atoms, it's about energy and where it's going

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