A rocket becomes progressively easier to accelerate as it travels through space. Why is this so?

Answer 1

Most of these answers are right. The three main issues are resistance, gravity and momentum.

As the rocket moves farther from the earth, the gravity becomes less and less.
As the rocket moves out of the atmosphere, the friction of air resistance disappears.
As the rocket burns its fuel, its mass becomes less and thus less force is required to accellerate it.

In general, the equation of motion for a rocket is:

F = (dP/dt) - b(dx/dt)

where P=momentum or (m*v) and b=friction/resistance of motion through a fluid.

Once out of the atmosphere, b=0 and that term disappears.

The first term represents the accelleration due to thrust minus the decelleration due to gravity.
This term, F=dP/dt, is different than the traditional F=ma because mass is not constant.
It is the true term for force and is normally F=d(mv)/dt.

In most common physics, mass is usually a constant and this is how we get F=ma:

Where F= ((v)d(m) + (m)d(v))/dt and in most cases, since mass is constant, the first term disappears and you are left with (m)d(v)/dt. And as you know d(v)/dt = a.

Sorry to go into too much detail, but someone above referenced F=ma, which in the case of rocket science, is a no-no.

Answer 2

through space and using our current technology, yes. If you start somewhere in space, then how hard it is to accelerate the rocket depends only on its mass, irrespective of the speed. With our current rocket technology, the rocket carries a lot of fuel. When you burn some of that fuel to accelerate, the rocket becomes lighter. So it becomes easier to accelerate further. Which is why the higher the ratio of fuel weight to total weight, the faster the rocket can go.
Then, if you were ever to get close to the speed of light, the mass of the rocket would progressively increase, and it would become harder and harder to accelerate it more.


Now if you meant "taking off from the Earth", then yes again. The engines have to do two things, (1) they have to accelerate the mass of the rocket (i.e. do the same job they'd have to do if starting from somewhere in space (see above), and (2) they have to cancel out the weight of the rocket.

The first bit depends only on the mass of the rocket, and I've said above, the mass will decrease as fuel is being used, so it will progressively become easier to accelerate. And the second bit depends on how close you are to the Earth, and the further away you get, the easier it will become.

Hope this helps

Answer 3

Nice question. A rocket becomes progressively easier to accelerate as it travels through space as there is vacuum in space which means that there is no external unbalanced force acting on the rocket. So, once it accelerates in the space it goes on moving till the crew inside it stops it. This theory is based upon the newton's first law of motion.

Answer 4

When it takes off from the surface of a planet you're right. Gravity decreases the further you get from the planet, so it becomes progressively easier to accelerate. The other consideration is, there's a limit to how much acceleration the crew can withstand. Say the limit is 4g. Then on liftoff the maximum acceleration of the rocket will be 3g because the Earth's gravity contributes 1g.

Answer 5

When a rocket lifts off from Earth, it needs more lift/energy to overcome the pull of Earth's gravity. Thus, it would be "difficult" to accelerate. However, once it is in the vacuum of space, there is no gravity, nor is there atmospheric resistance nor friction. So it requires less energy to increase its velocity through space (it is easier).

Answer 6

When taking off, the farther away from the Earth it gets, the more efficient its own engines will be because it is farther from gravity and the force due to gravity lessens.

Once it gets beyond a certain point, then the Sun's gravity will dominate and now the principle becomes...
the farther away from THE SUN it gets, the more efficient its own engines will be, for the same reason.

Travel towards the sun is a different story.

Answer 7

Because it has burned up much of its fuel, so the remaining mass to be accelerated is less.

F = ma

Less mass means less force needed to achieve the same acceleration.

Answer 8

At non-relativistic speeds this is true. And it's because the mass of the rocket becomes less as it burns its' fuel.


Doug

Answer 9

Because the mass is decreasing as it burns fuel, so it requires less thrust to accelerate.

Answer 10

If it is leaving a planet, the gravitational pull lessens.

If it is carrying a fuel that weighs a lot, the ship gets lighter as it goes. (this wouldn't apply to something with nuclear or ion propulsion, for instance.)