# Understanding Action & Reaction Forces

• accelerate23
In summary, the action and equal and opposite reaction principle explains that the rocket exerts a force on the fuel by ejecting it, and the fuel exerts an equal and opposite force on the rocket. This is due to the high pressure of the exhaust gases being emitted from the rocket engines. This process is initially inefficient, but becomes more efficient as the rocket gains speed. The presence of the ground can help lift the rocket in its initial stages, but is not necessary for the rocket to function. Additionally, the New York Times once published a now-retracted editorial claiming that rockets could not work in space due to a lack of something to push against.
accelerate23

The rocket imparts a force on the fuel by ejecting it , the ejected fuel exerts an equal, but oppositely directed force on the rocket.

Thanks!

It's all those exhaust gases emerging from the nozzles at super high speed that the rocket engines are emitting. At the back of the combustion chambers there is a high pressure that pushes up against the inside, raising the rocket, whilst the same pressure is pushing the gases out at the bottom. The momentum of all that high speed gas is equal to the momentum gained by the rocket.
At the start of the flight, the whole process is INCREDIBLY inefficient because there's a lot of force but not much distance raised. It gets better as the rocket starts to go faster.

PS you don't need the ground to be there for the gases to 'push against'. However, it's got to be true that, (as with a hovercraft) whilst on the ground, there will be a bit of excess pressure under the rocket, which will help to lift it the first meter or so. Above that, the gases can escape so easily that the pressure is not helped by the presence of the ground.

Thank you so much!

## 1. What are action and reaction forces?

Action and reaction forces are a pair of forces that occur simultaneously between two objects in contact. These forces are equal in magnitude and opposite in direction, as described by Newton's third law of motion.

## 2. How do action and reaction forces affect motion?

Action and reaction forces do not cancel each other out, as they act on different objects. However, they do result in a change in the motion of both objects, causing them to accelerate in opposite directions.

## 3. Can action and reaction forces occur in non-contact situations?

Yes, action and reaction forces can occur in non-contact situations. For example, the Earth exerts a gravitational force on objects, causing them to exert an equal and opposite reaction force on the Earth.

## 4. How do action and reaction forces relate to momentum?

According to Newton's second law of motion, the net force acting on an object is equal to the rate of change of its momentum. As action and reaction forces result in changes in the momentum of both objects, they are closely related to the concept of momentum.

## 5. Can the magnitude of action and reaction forces be different?

No, according to Newton's third law of motion, action and reaction forces are always equal in magnitude. However, the objects involved may have different masses, resulting in different accelerations.

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