regarding working principle of rocket in space?

Question

In earth atmosphere force of exhaust gases from rocket on to the atmosphere produces a reaction on the rocket in upward direction to lift it up. but how a rocket works in space as there is no atmosphere ?

Answer 1

Wrong. It is not the exhaust pushing against the atmosphere that gives the thrust for a rocket. It is the principle of conservation of momentum. If anything, the atmosphere hinders the propulsion of the rocket because of friction. In a vacuum, the momentum conservation still holds, but there is no friction from the atmosphere, so things work even better.

Answer 2

It is not the forces of the exhaust gasses on the atmosphere, it is the forces of the exhaust gasses directly on the rocket that cause it to move.

Think of two heavy weights squeezing a strong spring between them and held together with a latch. You open the latch and the spring pushes the weights apart. The spring does not push on the air or the ground or anything except the weights. The weights would be pushed apart in outer space just like anywhere else. If one weight is twice as heavy as the other, then the lighter weight will end up going twice as fast as the heavier weight. A rocket is like millions of tiny weights being pushed out the back of the rocket every second at thousands of mph. The tiny weights are exhaust gas molecules and the energy to push them comes not from a spring but from the burning of the fuel. And this happens every second, So the first second the 200 ton rocket pushes 1 ton of exhaust out the back at 10,000 mph so that the rocket can go the other way at 50 mph. The second second, the rocket pushes another ton of exhaust out the back and speeds up by another 50 mph to 100 mph. Actually it speeds up a little more than 50 mph, because it is lighter now, only 199 tons. When half the fuel is gone and it weighs only 100 tons, each ton of exhaust going out the back at 10,000 mph speeds up the rocket by 100 mph. It is really inefficient, filling up a 20 ton rocket with 200 tons of fuel and then throwing it all out the back in 10 minutes or less, but that is the only way we know to get to orbit now. That is why a 100 foot tall rocket is needed to put a 10 foot tall satellite in orbit. The other 90 feet of rocket is all fuel tanks to hold all that fuel.

Answer 3

It is not the force of the exhaust against anything that propels the rocket. According the Newton's laws of motion, for every action there is an equal and opposite reaction. The mass of the exhaust accelerating out the rear of the rocket produces a reaction of equal momentum on the rocket.

Another example is when a gun is fired, the bullet has low mass but high velocity when it exits the barrel. The gun reacts in the opposite direction but because is has a significantly greater mass than the bullet the expanding gasses, its velocity is much lower but momentum in conserved.

Answer 4

It is not really the force of exhaust gasses on the atmosphere
that drives the rocket foreward..
It is the force of the exhaust gasses leaving the rocket...
Every action has an equal but opposite reaction...

Answer 5

The atmosphere has nothing to do with it. Force is force even in a vacuum.

Answer 6

I'd vote for Common Sense's answer (plain English is always better in my book), but I thought you'd like to know that scientists debated this question before the first manned space mission. So your question puts you in good company.

Answer 7

It uses the same theory - not to push but to get pushed - In the opposite direction.