Tag Info

New answers tagged

0

If by "slow down" you mean "decelerate the rocket as it moves through space" the answer is no. Once the ship as begun traveling at a constant linear speed $v$ and begun rotation at a constant angular speed $\omega$ it will continue to move with a constant velocity (both linear and angular) in the absence of any net forces or torques. The object will have a ...


0

It can be proven that if you just want to know the motion the center of mass of a system of particles (or a continuous extended body), you can just calculate the vector sum of the force vectors on each particle (or the integral of the infinitesimal force on each infinitesimal bit of mass dm in a continuous extended body), and then treat this total force ...


0

I think there is no influence of rotation, regardless of rotation plane and direction vector. The center of mass will move with the same speed. Newton's First Law of motion should be enough to prove it: When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an ...


2

Let's address the linear problem first. Both the approaches you have written here are correct: they are essentially the same approach to slightly different situations. The first is the clearer one because it is thinking in terms of momentum conservation of the whole system, which is unquestionably the clearest way to think about these kinds of problems. In ...


1

If we ignore neutrinos, which are weakly interacting, radioactivity is still classified as alpha beta and gamma. The energies are of order MeV. Of these three, only gamma is neutral and has a chance to cross the atmosphere . Then one has to take into account the 1/r**2 diminution of the flux for the large distances . To localize a source another ...


2

Not possible in practice, even though neutrinos emitted by the Plutonium might be used in principle if we ever found a way of intercepting them with almost 100% efficiency. However, there is/was a scheme to use neutrino analysis to determine whether a reactor is being used to create Plutonium


4

Generally true because during the acceleration phase fuel that will later be burned is accelerated along with the ship, whereas upon deceleration the overall mass of the ship will be smaller, requiring less fuel to slow it.


4

Have you ever sat on a wobbly, four-legged chair? That can't happen with a three-legged chair. A three-legged chair is stable. Four legs is one leg too many. A four-legged lander would need to adjust the lengths of the legs to stabilize it. Update Aside: The English word you are seeking is tetrahedron. Now that the intent of the question is clear, the ...


3

Well still is a little tricky to define in space, but assuming it isn't close enough to any other object to feel its gravity it will just stay there. Until you use its engines. Rocket engines don't need anything to push against, throwing the exhaust out of the back is what pushes it forward. Think of it as like the recoil of a gun when you fire a bullet ...


2

The simplest way to get this intuitively is to consider a rocket where the exhaust gasses escape in two opposite directions. So, there is a nozzle at one side and also the opposite side. In this case, the rocket will go nowhere. The chemical reactions produce gasses at high temperature and pressure and they then accelerate and escape in both directions. If ...


0

The best common example is often shown in HS physics classes. A student in a low friction chair holds a CO2 fire extinguisher and points it in a safe direction. When they pull the trigger and release CO2 gas moving very fast from the nozzle of the fire extinguisher that rapidly moving gas leaving the system (chair student and gas bottle) causes the system to ...


5

A model I encountered as a kid, back when the Space Race was in full swing, is still the simplest explanation I've found: Think about an inflated balloon with its neck closed. It doesn't go anywhere, because the pressure in all directions is equal. (Which is what keeps it inflated, too.) Now open the neck. What makes the balloon fly around isn't actually ...


6

I'm a little confused why you ask about GR at the very end of your question. If your question is simply how a rocket is able to accelerate in space without having anything to "push" off, then we can tackle your question pretty well with classical mechanics. Newton's Third Law has its limitations at times, but for this question it will work just fine. ...


1

I am wondering how the rockets could thrust in the empty space and move in the opposite direction. In very simplistic terms the rocket motor thrusts against the closed end of the nozzle. Once the gas leaves the nozzle it no longer has any interaction with the rocket - there is no need for it to 'hit' anything else.


20

Newton's third law is pretty near to the mark. All of the phenomena you cite stem from the principle of conservation of momentum in an isolated system, itself ultimately a result (through Noether's theorem) of the fact the physical description of that isolated system is unchanged if we shift the spatial origin of our co-ordinate system. So, if you're in ...


5

No need to call the general relativity. You can understand it using only classical mecanics laws. If you are on a skateboard, and throw a mass in front of you, you will move backwards. As long as the mass does not hit the floor, the center of mass of {you+the mass} is the same, however you did move. The rocket engine ejects gaz from combustion. The ...


6

If I'm not wrong, it's basically the same principle in which an astronaut would throw something in empty space and, with so, move in the opposite direction. It's not thrusting against something but throwing energy and power by burning fuel according to the law of inertia... I could be wrong so I'd like someone more knowledgeable to double-check, please :)



Top 50 recent answers are included