How does a rocket work in a vacuum

[tinman]

A jet boat has an unlimited supply of water that it draws from underneath the boat.  It then uses Newtons 3rd law of motion by ejecting the water (equal and opposite reaction)  to travel horizontally across  the force of gravity. The water goes one way the boat goes the other. I get it.   

Unfortunately a rocket does not have an unlimited supply of water or fuel or anything to push away from itself to invoke 3rd law of motion and it also has to travel vertically straight up against the force of gravity and not horizontally across the force of gravity. A rocket has a limited  supply of fuel it can burn to generate thrust and that fuel is quickly exhausted. By the time the rocket reaches 100km (if it even reaches that height) and the multiple stages of the rocket that contain the fuel have been exhausted and separated from the rest of the rocket and now with out fuel to push out I still have no idea how it travels the next 60km straight up into space.

As I continue to state everyone has great theories but that is all they are, theories and a theory needs to be proven.

This is basic high school physics. Although NASA may say Don't worry this is rocket science we can quickly verify the facts with data.  WE NEED THE DATA and without the data we are just making stuff up.

Like all machines both here on earth,and out in space-->once you run out of fuel,then the force moving that machine stop's. But in space,you have no resistance,and so the machine will maintain it's maximum velocity reached -until it encounters another force that impacts it's motion.

If the rocket ran out of fuel before it reached a point of either orbit or had escaped the earths gravity field,then it would simply be pulled back down to earth,and impact the surface. As they do not do that(mostly ),then we can assume that one of the two above is true.

Brad

[LibreEnergia]

Unfortunately a rocket does not have an unlimited supply of water or fuel or anything to push away from itself to invoke 3rd law of motion and it also has to travel vertically straight up against the force of gravity and not horizontally across the force of gravity. A rocket has a limited  supply of fuel it can burn to generate thrust and that fuel is quickly exhausted. By the time the rocket reaches 100km (if it even reaches that height) and the multiple stages of the rocket that contain the fuel have been exhausted and separated from the rest of the rocket and now with out fuel to push out I still have no idea how it travels the next 60km straight up into space.

Rockets destined for orbit do not go straight up, except initially.  The trajectory curves over and flys parallel to the earth. Once it runs out of fuel the thrust stops. If it has not reached orbital velocity by that time then it will come back down to earth.

In orbit the rocket is always "falling towards earth". It's just that it's tangential velocity is high enough for it to always miss.

[Nink]

If the rocket ran out of fuel before it reached a point of either orbit or had escaped the earths gravity field,then it would simply be pulled back down to earth,and impact the surface. As they do not do that(mostly ),then we can assume that one of the two above is true.

Brad

I am really confused when I watch a video of the Apollo Launch with stages ejected and the last height reading is 92.8km before they cut the camera just as they are about to cross the Karman line as it is approaching the edge of the atmosphere. The rocket is a lot lighter now then when we launched and there is a velocity of 2880 m/s but we are only 60% of the way to low earth orbit at 160km where as you say we no longer need fuel to maintain velocity. But how much fuel do we have left to get from that point to escape the pull of gravity  (ignoring the fact I don't believe the propulsion method used to take us to the 92.8 km  point will work past the 100km point as there is no atmosphere).    We also don't need to worry about the fuel to get to the moon, land on the moon, take off from the moon and fly back to earth since neither of us believe that part happened. 

Does anyone have all the data  for this trip.  The person calling out the data is different than what is on the display,

Example
Video time  https://www.youtube.com/watch?v=F0Yd-GxJ_QM&feature=youtu.be&t=48
+30 seconds syncs clocks Says 30 second shows 30 seconds

but video time  https://youtu.be/F0Yd-GxJ_QM?t=74
at 56 second mark says altitude  2 miles but screen says 5.06 km but that is actually 3.2 miles

now
Video time https://www.youtube.com/watch?v=F0Yd-GxJ_QM&t=1m35s
Says 2195 ft / s
Screen  460 m/s   
Convert 669 m/s

Video time https://youtu.be/F0Yd-GxJ_QM?t=127
Says 4000 ft /s    
Screen 1040 m/s 
Convert 1219 m/s

Video time https://youtu.be/F0Yd-GxJ_QM?t=201

Syncs clocks
Says 3 minutes
screen 3 min 3 seconds

says range 70 miles
convert range 112km

Says altitude 43 miles
convert 69km
screen says 87km

says 9300  f/t per second
convert 2834 m/s
screen 2870 m/s

[Nink]

Maybe they are going straight up,and only look like they are arcing because the earth is spinning
As your view point is from the spinning earth,the rocket would appear to arc in accordance to that spin. But what if your view point was from a fixed point in space--would the rocket appear to arc then?.

Brad

I checked your theory with the voice over data (I ignored the screen data) looks like you are correct.  Earth is spinning at 1,674.4 km/h https://en.wikipedia.org/wiki/Earth%27s_rotation  and at the 3.06 mark we can use the voice data. Quick bit of trigonometry the earth should have rotated 85km at that time math for rocket shows 88km so there could be a slight margin of error on vertical tragectory but I think you are right.  Rocket travels straight up but earth rotates below it. At least until the 69km mark.  What worries me is if the voice data is correct and screen data is wrong we are now only at 69km altitude we still have 91km to go until LOE.

Math works but we need data. 

[allcanadian]

@Nink

I still don't have an answer.   I have been told  that F=MA and Carroll and NASA say F=MV in space. [/size]NASA do not  say F=MA in a vacuum like everyone else here is saying, NASA says F=MV[/size] [/size]https://www.nasa.gov/pdf/153415main_Rockets_How_Rockets_Work.pdf[/font][/size]  and then NASA make the bold statement[/size]"In real rocket science, many other things also come into play"[/size] I have no idea what that statement means and I have no data to model this against.   I think we all fully understand F=MA when we are in the presence of an atmosphere or firing a rocket on the ground with earth to push against but I don't understand how we move from F=MA to F=MV, especially when we have no atmosphere and still have the force of gravity to contend with.  [/size]

Many times people give a textbook answer however fundamentally they do not actually understand what it means. I believe the word you are looking for is Inertia which is why a mass resists changes in motion.


Imagine you are on a boat and you throw a bowling ball to the left which makes the boat go to the right. Some may say it is the Mass Acceleration or the exchange there of but this does not really explain anything. Others may say it is the conservation of momentum or MV=MV but again this really does not explain anything fundamentally. In our boat example when you throw/push the bowling ball to the left the inertia of the ball resists your pushing force to accelerate it which produces a force in the opposite direction on you thus you and the boat move to the right.


From your question I think you are looking for more and this is a good sign even if most here cannot see the problem. The bowling ball cannot resist anything and it cannot produce a counter-force on you nor the boat and there is no momentum exchange. To do so implies some mysterious force we call Inertia has caused the mass to act on itself in itself which violates the laws of physics. An object cannot act on nothing or act on itself however when we speak of Inertia which is the cause of momentum and a property of mass this is exactly what we are saying hence all the confusion. As I said it is a very good sign that you see the problem and have questioned it.


What is Inertia?. Let's think about this, I am in space and I push on my bowling ball and it resists my pushing force somehow producing a counter force on me in the opposite direction. Some say the ball is pushing off me just as I am pushing off it but this is not correct and two wrongs do not make a right. If the ball had no inertia then it would move and I would not move at all. The property of inertia is not a property of mass but a property of the space the mass occupies. In a nutshell all the electromagnetic waves in the universe which fill every space everywhere act on each individual particle of the object or mass influencing it's motion. This also relates to the supposedly mass-less particles which have no inertia and really confuse the hell out of everyone. What they are actually saying is the particle lacks a property by which they measure the mass which is of course Inertia. A mass may seem to resist a change in motion by apparently acting on nothing or acting on itself however intuitively we know this cannot be true.


This also relates to why Einstein said- nothing happens until something moves, also when something moves the whole universe moves with it...literally. People don't like to talk about Inertia because they find it disturbing. You see if people actually understood what it is fundamentally then we could modify or negate this external influence on matter. A mass with no inertia would take almost no energy to accelerate to any velocity. Obviously this is a real problem for many psychologically which is why Inertia is generally considered a taboo subject.


AC